I ndispensable for life, ultraviolet (UV) radiation is also the cause of numerous skin disorders, including skin cancers. As more and more people spend time in the sun, the incidence of photodermatitis increases, and more must be done to provide protection to those who choose to, or are required to, spend a lot of time in the sun. Sunscreen manufacturers are developing new formulations and offering more information on the use of their products to improve the level of protection that these products provide. Sunscreens are now designed to protect not only against UVB light but also UVA light. Those sunscreens have shown their efficacy in prevention of numerous photodermatitis. In this article, we’ll highlight insights Michele R. Verschoore, M.D., a dermatologist and clinical pharmacologist for L’Oréal Research, shared at the American Academy of Dermatology meeting about the chemistry of sunscreens. The Importance of Sunscreen Few would argue the dangers of UV radiation. The evidence of UV damage is significant, and most experts agree that UV radiation is carcinogenic for humans. In fact, non-melanoma skin cancer is most common on UV-exposed skin sites: the head, neck, arm and hands. With that in mind, it’s important for everyone to protect his or her skin from UV radiation. Yet, people spend a lot of time in the sun, either in leisure activities or because of their professions. If an individual is going to spend a lot of time in the sun and is going to be exposed to a significant amount of UV radiation, then applying sunscreen to any exposed skin is critical. UVA and UVB are the two primary forms of UV radiation that reach the surface of the Earth. UVB does not penetrate deep into the skin, and is generally what causes sunburn. With UVA, the penetration into skin is deeper, and the biological effects of UVA radiation are significantly more profound. UVA represents almost 95% of the UV that reaches the skin. That means there’s at least 18 times more UVA than UVB. Like visible light, UVA penetrates glass. However, UVB is filtered by window glass so an individual may not get sunburn, but there is risk of accumulation of large UVA doses for people who spend a lot of time behind glass, like truck drivers. “UVA radiation provokes dryness, redness, pigmentation, wrinkles and a host of other problems. In fact, between 80% to 90% of skin damage can be attributed to sun exposure,” says Dr. Verschoore. “UVA provokes some damage to DNA and other molecules including urocanic acid. The cellular effects of UV light include suppression, activation or inhibition of some enzymes, longer cell alteration and inflammation of cells.” Formulation of Sunscreens According to Dr. Verschoore, the goal of sunscreen formulation is a final product able to protect people from UVB and UVA and to prevent, with regular use, the short-term effects of erythema and long-term effects like photodamage and pigmentation. Typically, a sunscreen uses a combination of organic filters and physical filters to either reflect or absorb UV radiation to achieve this goal. “In addition to providing a well-balanced, broad-spectrum filtration of UVB and UVA, the sunscreen formulation must also be chemically photo-stable under UV light when used on human skin, chemically stable in packaging under different conditions, and have negligible transdermal absorption because we need to keep this protection at the surface,” says Dr. Verschoore. The product must also be safe for use in large amounts, non-irritating, user-friendly, invisible and non-staining on the clothes. The cosmetic look of the sunscreen is important so that people apply the proper amount. Finally, it must have an acceptable price for use in large quantities. So how do manufacturers select sunscreen’s active ingredients? It depends on the spectral efficacy. According to Dr. Verschoore, in the United States, only four UVA filters are available: avobenzone (octyl methoxycinnamate), oxybenzone (2-Hydroxy-4-methoxybenzophenone), titanium dioxide and zinc oxide. Of the four, avobenzone, also known as Parsol 1789, is the most efficient. In Europe and other parts of the world, there are new UVA filters, such as Mexoryl SX, Mexoryl XL, Tinosorb S and Tinosorb M, but they have not been approved for use in the US. Titanium dioxide and zinc oxide are preferable UVA/UVB sunscreens because of their efficiency and low irritation. “In many countries, avobenzone has been used in combination with titanium dioxide and zinc oxide to increase the protection in the UVA range,” says Dr. Verschoore. Dramatically increasing the level of an ingredient may not have a corresponding increase in the level of protection. “If you increase the level of zinc oxide, of course you are going to increase the UVA protection, but not a lot,” says Dr. Verschoore. “For example, with 3% of zinc oxide you are going to get a persistent pigment darkening (PPD) of UVA protection around 3, and with 10% you are going to get 4 or 5. So you can see that the difference is not huge.” The efficacy of physical sunscreen, such as zinc oxide, depends on different factors like refractive index, size of particles, dispersion of the formulation and also the film thickness. The refractive index of inorganic pigments is very important to know when formulating a sunscreen. The size of the particles is also important as the smaller the particles, the lower the protection. So, in fact, you have to take into account the ratio, efficacy and cosmetic elements. Also, zinc oxide absorbs more in the UVA range, but titanium dioxide is more efficient in the UVB range. Another important factor is the photo-stabilization of the ingredients used to ensure that the UV protection remains constant. “We need to consider the photo-stability of an ingredient, as some molecules lose their efficacy quickly when exposed to UV radiation and other factors,” says Dr. Verschoore. “Therefore, it is important to photo-stabilize ingredients. The sunscreen formulation is, in fact, a combination of sunscreen solvent and emulsifiers and other agents to improve the photo-resistance.” Evaluation of Product In the United States, the FDA regulates sunscreens, treating them as over-the-counter drugs, and has established standards for labeling sunscreens. In terms of sun protection, sunscreen is measured by its sun protection factor (SPF). A short definition of the SPF, in fact, is a ratio of the minimal erythemal dose on skin protected by the product and the minimal erythemal dose on unprotected skin. There are three categories, SPF 2 to SPF 12 with a minimal sunburn protection, SPF 12 to SPF 30 moderate sunburn protection and above 30 high sunburn protection. “However, you must also be aware of the level of UVA protection provided by the formulation. Two different formulations may provide the same SPF but may provide dramatically different UVA protections,” says Dr. Verschoore. “But how do we evaluate this UVA protection? There are some in-vivo methods like PPD and IPD and some in-vitro methods.” There are a few ways to evaluate UVA protection — in vivo and in vitro. In-vivo methods include PPD and immediate pigment darkening (IPD). The advantages to PPD are that the response is known and stable extending over the whole UVA, the response lasts from 2 hours to 24 hours after irradiation, the law of reciprocity is valid and the method is calibrated. There are some inconveniences because photo type 1 is limited, it uses high UVA doses and it is expensive because of the need for at least 10 subjects. The advantage of the IPD method is that it uses low UV doses. UVA protection evaluation depends on the country. In the United States, there is no official method. In Europe and Japan, they use the PPD. In Australia, they use in-vitro evaluation for broad-spectrum sunscreens. “We would like to see a UVA evaluation and to have a classification according to the SPF/PPD ratio,” says Dr. Verschoore. “Because it makes sense to have high UVA protection when you have the high SPF.” The proposal is to have a ratio above 5 with no UVA protection, a ratio between 4 and 5 with low protection, a ratio between 3 and 4 with normal protection and a ratio of less than 3 with high protection. Application To achieve maximum effectiveness, sunscreens should be applied at least 20 minutes before exposure to the sun and should be reapplied every 2 hours. In addition, sunscreens should also be reapplied after swimming or strenuous activity, even water-resistant sunscreens. Sunscreens should be applied at the rate of 2 milligrams per square centimeter. This translates to roughly 1 ounce of product for each application, more for larger people, less for children. A good rule is to apply two finger lengths to each major body surface. So you would apply two finger lengths to your arms, two lengths to your back, two to your chest and abdomen, two to your upper legs, two to your lower legs and feet. “The FDA does not permit manufacturers to claim all-day protection, since to provide protection, virtually all products have to be reapplied every 2 hours,” says Dr. Verschoore. “Water-resistant formulations must past rigorous testing to determine that they won’t come off when swimming or sweating, but even these should be reapplied after the individual gets wet.” Sunscreen Safety The safety dose for a sunscreen looks like a dose for a drug, for a medical product, because we have to evaluate the acute oral and dermal toxicity, the dermal and high irritation, photo irritation, sensitization, photo sensitization, chronic, oral and topical teratology, fertility, peri- and post-natal toxicity, in-vitro genetic toxicity, photo genetic toxicity in vitro, in-vivo genetic toxicity, and the penetration. “There was a concern a few years ago about the fact if you protect too much you are not able to get your vitamin D. So there were some studies showing, in fact, with good protection, both in UVB and UVA, you are able to have normal vitamin D levels,” says Dr. Verschoore. “In a study, subjects who were protected by sunscreen and people who were not protected had the same level of vitamin D synthesis.” When evaluating sunscreen safety, it is important to evaluate the skin penetration of a product, because the UVA filters must remain on the surface of the skin. According to Dr. Verschoore, studies of the primary UVA filters, oxybenzone, OMC, octocrylene and octyl salicylate, showed that these products remained on the surface of the skin with negligible penetration. A question about the safety of sunscreen in children often arises. “If you consider skin permeability, there is no difference between children and adults,” says Dr. Verschoore. “The susceptibility to irritation is the same for children and adults. But, the major difference for risk assessment is that children have a larger body surface area relative to their body weight.” That means children have a greater exposure to a topically applied penetrating substance than adults. And children have a higher exposure on a body weight basis to UV radiation, and, typically, kids play outside more than adults. That’s why there are some guidelines to evaluate the safety margin for sunscreen. Manufacturers need to consider the amount of formulation that is applied as well as the concentration of each active ingredient in order to be able to evaluate the absorption. Expiration of Sunscreens According to Dr. Verschoore, most sunscreen products remain effective in an unopened container for at least 1 or 2 years, with some companies providing a guarantee of stability for 3 years. However, for the remaining product in an open container, there is no way to determine how long that product will remain stable. The effectiveness of any sunscreen product that has been opened for more than a year may be significantly compromised. You may want to recommend that patients dispose of all products from the previous season that have been opened. Efficacy of Sunscreens Sunscreens can be very effective in protecting the cells of the skin from being modified by UV radiation. For example, in an evaluation study, melanocytes that were UV protected did not change their shapes when exposed to UVA radiation. Those that were unprotected had their shape changed dramatically by UVA radiation. Another study examined the ability of sunscreens to prevent solar urticaria in patients with a history with the condition. Using sunscreen with a SPF of 60 and an UVA protection level of 15, the study showed that the condition could be prevented in these patients with the proper application of sunscreen. Conclusion While UV radiation can have some positive effects, such as vitamin D synthesis, increase in stratum corneum thickness and resistance and anti-inflammatory effects, it also has serious negative effects, including aging of the skin, suppression of the immune system and even cancer. Despite these dangers, many people still do not protect themselves from UV radiation, and those that do often are unaware of how to use sunscreen products correctly to achieve the maximum protection. “A carefully chosen and properly applied sunscreen can protect the wearer from the damage created by UV radiation,” says Dr. Verschoore. “Physicians need to educate their patients about the importance of wearing sunscreen, the need to select the proper sunscreen and how to use and apply sunscreens properly.” Editor’s Note: Henry Lim, M.D., of Detroit, MI, also contributed to this article.
Evaluating Sunscreen
I ndispensable for life, ultraviolet (UV) radiation is also the cause of numerous skin disorders, including skin cancers. As more and more people spend time in the sun, the incidence of photodermatitis increases, and more must be done to provide protection to those who choose to, or are required to, spend a lot of time in the sun. Sunscreen manufacturers are developing new formulations and offering more information on the use of their products to improve the level of protection that these products provide. Sunscreens are now designed to protect not only against UVB light but also UVA light. Those sunscreens have shown their efficacy in prevention of numerous photodermatitis. In this article, we’ll highlight insights Michele R. Verschoore, M.D., a dermatologist and clinical pharmacologist for L’Oréal Research, shared at the American Academy of Dermatology meeting about the chemistry of sunscreens. The Importance of Sunscreen Few would argue the dangers of UV radiation. The evidence of UV damage is significant, and most experts agree that UV radiation is carcinogenic for humans. In fact, non-melanoma skin cancer is most common on UV-exposed skin sites: the head, neck, arm and hands. With that in mind, it’s important for everyone to protect his or her skin from UV radiation. Yet, people spend a lot of time in the sun, either in leisure activities or because of their professions. If an individual is going to spend a lot of time in the sun and is going to be exposed to a significant amount of UV radiation, then applying sunscreen to any exposed skin is critical. UVA and UVB are the two primary forms of UV radiation that reach the surface of the Earth. UVB does not penetrate deep into the skin, and is generally what causes sunburn. With UVA, the penetration into skin is deeper, and the biological effects of UVA radiation are significantly more profound. UVA represents almost 95% of the UV that reaches the skin. That means there’s at least 18 times more UVA than UVB. Like visible light, UVA penetrates glass. However, UVB is filtered by window glass so an individual may not get sunburn, but there is risk of accumulation of large UVA doses for people who spend a lot of time behind glass, like truck drivers. “UVA radiation provokes dryness, redness, pigmentation, wrinkles and a host of other problems. In fact, between 80% to 90% of skin damage can be attributed to sun exposure,” says Dr. Verschoore. “UVA provokes some damage to DNA and other molecules including urocanic acid. The cellular effects of UV light include suppression, activation or inhibition of some enzymes, longer cell alteration and inflammation of cells.” Formulation of Sunscreens According to Dr. Verschoore, the goal of sunscreen formulation is a final product able to protect people from UVB and UVA and to prevent, with regular use, the short-term effects of erythema and long-term effects like photodamage and pigmentation. Typically, a sunscreen uses a combination of organic filters and physical filters to either reflect or absorb UV radiation to achieve this goal. “In addition to providing a well-balanced, broad-spectrum filtration of UVB and UVA, the sunscreen formulation must also be chemically photo-stable under UV light when used on human skin, chemically stable in packaging under different conditions, and have negligible transdermal absorption because we need to keep this protection at the surface,” says Dr. Verschoore. The product must also be safe for use in large amounts, non-irritating, user-friendly, invisible and non-staining on the clothes. The cosmetic look of the sunscreen is important so that people apply the proper amount. Finally, it must have an acceptable price for use in large quantities. So how do manufacturers select sunscreen’s active ingredients? It depends on the spectral efficacy. According to Dr. Verschoore, in the United States, only four UVA filters are available: avobenzone (octyl methoxycinnamate), oxybenzone (2-Hydroxy-4-methoxybenzophenone), titanium dioxide and zinc oxide. Of the four, avobenzone, also known as Parsol 1789, is the most efficient. In Europe and other parts of the world, there are new UVA filters, such as Mexoryl SX, Mexoryl XL, Tinosorb S and Tinosorb M, but they have not been approved for use in the US. Titanium dioxide and zinc oxide are preferable UVA/UVB sunscreens because of their efficiency and low irritation. “In many countries, avobenzone has been used in combination with titanium dioxide and zinc oxide to increase the protection in the UVA range,” says Dr. Verschoore. Dramatically increasing the level of an ingredient may not have a corresponding increase in the level of protection. “If you increase the level of zinc oxide, of course you are going to increase the UVA protection, but not a lot,” says Dr. Verschoore. “For example, with 3% of zinc oxide you are going to get a persistent pigment darkening (PPD) of UVA protection around 3, and with 10% you are going to get 4 or 5. So you can see that the difference is not huge.” The efficacy of physical sunscreen, such as zinc oxide, depends on different factors like refractive index, size of particles, dispersion of the formulation and also the film thickness. The refractive index of inorganic pigments is very important to know when formulating a sunscreen. The size of the particles is also important as the smaller the particles, the lower the protection. So, in fact, you have to take into account the ratio, efficacy and cosmetic elements. Also, zinc oxide absorbs more in the UVA range, but titanium dioxide is more efficient in the UVB range. Another important factor is the photo-stabilization of the ingredients used to ensure that the UV protection remains constant. “We need to consider the photo-stability of an ingredient, as some molecules lose their efficacy quickly when exposed to UV radiation and other factors,” says Dr. Verschoore. “Therefore, it is important to photo-stabilize ingredients. The sunscreen formulation is, in fact, a combination of sunscreen solvent and emulsifiers and other agents to improve the photo-resistance.” Evaluation of Product In the United States, the FDA regulates sunscreens, treating them as over-the-counter drugs, and has established standards for labeling sunscreens. In terms of sun protection, sunscreen is measured by its sun protection factor (SPF). A short definition of the SPF, in fact, is a ratio of the minimal erythemal dose on skin protected by the product and the minimal erythemal dose on unprotected skin. There are three categories, SPF 2 to SPF 12 with a minimal sunburn protection, SPF 12 to SPF 30 moderate sunburn protection and above 30 high sunburn protection. “However, you must also be aware of the level of UVA protection provided by the formulation. Two different formulations may provide the same SPF but may provide dramatically different UVA protections,” says Dr. Verschoore. “But how do we evaluate this UVA protection? There are some in-vivo methods like PPD and IPD and some in-vitro methods.” There are a few ways to evaluate UVA protection — in vivo and in vitro. In-vivo methods include PPD and immediate pigment darkening (IPD). The advantages to PPD are that the response is known and stable extending over the whole UVA, the response lasts from 2 hours to 24 hours after irradiation, the law of reciprocity is valid and the method is calibrated. There are some inconveniences because photo type 1 is limited, it uses high UVA doses and it is expensive because of the need for at least 10 subjects. The advantage of the IPD method is that it uses low UV doses. UVA protection evaluation depends on the country. In the United States, there is no official method. In Europe and Japan, they use the PPD. In Australia, they use in-vitro evaluation for broad-spectrum sunscreens. “We would like to see a UVA evaluation and to have a classification according to the SPF/PPD ratio,” says Dr. Verschoore. “Because it makes sense to have high UVA protection when you have the high SPF.” The proposal is to have a ratio above 5 with no UVA protection, a ratio between 4 and 5 with low protection, a ratio between 3 and 4 with normal protection and a ratio of less than 3 with high protection. Application To achieve maximum effectiveness, sunscreens should be applied at least 20 minutes before exposure to the sun and should be reapplied every 2 hours. In addition, sunscreens should also be reapplied after swimming or strenuous activity, even water-resistant sunscreens. Sunscreens should be applied at the rate of 2 milligrams per square centimeter. This translates to roughly 1 ounce of product for each application, more for larger people, less for children. A good rule is to apply two finger lengths to each major body surface. So you would apply two finger lengths to your arms, two lengths to your back, two to your chest and abdomen, two to your upper legs, two to your lower legs and feet. “The FDA does not permit manufacturers to claim all-day protection, since to provide protection, virtually all products have to be reapplied every 2 hours,” says Dr. Verschoore. “Water-resistant formulations must past rigorous testing to determine that they won’t come off when swimming or sweating, but even these should be reapplied after the individual gets wet.” Sunscreen Safety The safety dose for a sunscreen looks like a dose for a drug, for a medical product, because we have to evaluate the acute oral and dermal toxicity, the dermal and high irritation, photo irritation, sensitization, photo sensitization, chronic, oral and topical teratology, fertility, peri- and post-natal toxicity, in-vitro genetic toxicity, photo genetic toxicity in vitro, in-vivo genetic toxicity, and the penetration. “There was a concern a few years ago about the fact if you protect too much you are not able to get your vitamin D. So there were some studies showing, in fact, with good protection, both in UVB and UVA, you are able to have normal vitamin D levels,” says Dr. Verschoore. “In a study, subjects who were protected by sunscreen and people who were not protected had the same level of vitamin D synthesis.” When evaluating sunscreen safety, it is important to evaluate the skin penetration of a product, because the UVA filters must remain on the surface of the skin. According to Dr. Verschoore, studies of the primary UVA filters, oxybenzone, OMC, octocrylene and octyl salicylate, showed that these products remained on the surface of the skin with negligible penetration. A question about the safety of sunscreen in children often arises. “If you consider skin permeability, there is no difference between children and adults,” says Dr. Verschoore. “The susceptibility to irritation is the same for children and adults. But, the major difference for risk assessment is that children have a larger body surface area relative to their body weight.” That means children have a greater exposure to a topically applied penetrating substance than adults. And children have a higher exposure on a body weight basis to UV radiation, and, typically, kids play outside more than adults. That’s why there are some guidelines to evaluate the safety margin for sunscreen. Manufacturers need to consider the amount of formulation that is applied as well as the concentration of each active ingredient in order to be able to evaluate the absorption. Expiration of Sunscreens According to Dr. Verschoore, most sunscreen products remain effective in an unopened container for at least 1 or 2 years, with some companies providing a guarantee of stability for 3 years. However, for the remaining product in an open container, there is no way to determine how long that product will remain stable. The effectiveness of any sunscreen product that has been opened for more than a year may be significantly compromised. You may want to recommend that patients dispose of all products from the previous season that have been opened. Efficacy of Sunscreens Sunscreens can be very effective in protecting the cells of the skin from being modified by UV radiation. For example, in an evaluation study, melanocytes that were UV protected did not change their shapes when exposed to UVA radiation. Those that were unprotected had their shape changed dramatically by UVA radiation. Another study examined the ability of sunscreens to prevent solar urticaria in patients with a history with the condition. Using sunscreen with a SPF of 60 and an UVA protection level of 15, the study showed that the condition could be prevented in these patients with the proper application of sunscreen. Conclusion While UV radiation can have some positive effects, such as vitamin D synthesis, increase in stratum corneum thickness and resistance and anti-inflammatory effects, it also has serious negative effects, including aging of the skin, suppression of the immune system and even cancer. Despite these dangers, many people still do not protect themselves from UV radiation, and those that do often are unaware of how to use sunscreen products correctly to achieve the maximum protection. “A carefully chosen and properly applied sunscreen can protect the wearer from the damage created by UV radiation,” says Dr. Verschoore. “Physicians need to educate their patients about the importance of wearing sunscreen, the need to select the proper sunscreen and how to use and apply sunscreens properly.” Editor’s Note: Henry Lim, M.D., of Detroit, MI, also contributed to this article.
I ndispensable for life, ultraviolet (UV) radiation is also the cause of numerous skin disorders, including skin cancers. As more and more people spend time in the sun, the incidence of photodermatitis increases, and more must be done to provide protection to those who choose to, or are required to, spend a lot of time in the sun. Sunscreen manufacturers are developing new formulations and offering more information on the use of their products to improve the level of protection that these products provide. Sunscreens are now designed to protect not only against UVB light but also UVA light. Those sunscreens have shown their efficacy in prevention of numerous photodermatitis. In this article, we’ll highlight insights Michele R. Verschoore, M.D., a dermatologist and clinical pharmacologist for L’Oréal Research, shared at the American Academy of Dermatology meeting about the chemistry of sunscreens. The Importance of Sunscreen Few would argue the dangers of UV radiation. The evidence of UV damage is significant, and most experts agree that UV radiation is carcinogenic for humans. In fact, non-melanoma skin cancer is most common on UV-exposed skin sites: the head, neck, arm and hands. With that in mind, it’s important for everyone to protect his or her skin from UV radiation. Yet, people spend a lot of time in the sun, either in leisure activities or because of their professions. If an individual is going to spend a lot of time in the sun and is going to be exposed to a significant amount of UV radiation, then applying sunscreen to any exposed skin is critical. UVA and UVB are the two primary forms of UV radiation that reach the surface of the Earth. UVB does not penetrate deep into the skin, and is generally what causes sunburn. With UVA, the penetration into skin is deeper, and the biological effects of UVA radiation are significantly more profound. UVA represents almost 95% of the UV that reaches the skin. That means there’s at least 18 times more UVA than UVB. Like visible light, UVA penetrates glass. However, UVB is filtered by window glass so an individual may not get sunburn, but there is risk of accumulation of large UVA doses for people who spend a lot of time behind glass, like truck drivers. “UVA radiation provokes dryness, redness, pigmentation, wrinkles and a host of other problems. In fact, between 80% to 90% of skin damage can be attributed to sun exposure,” says Dr. Verschoore. “UVA provokes some damage to DNA and other molecules including urocanic acid. The cellular effects of UV light include suppression, activation or inhibition of some enzymes, longer cell alteration and inflammation of cells.” Formulation of Sunscreens According to Dr. Verschoore, the goal of sunscreen formulation is a final product able to protect people from UVB and UVA and to prevent, with regular use, the short-term effects of erythema and long-term effects like photodamage and pigmentation. Typically, a sunscreen uses a combination of organic filters and physical filters to either reflect or absorb UV radiation to achieve this goal. “In addition to providing a well-balanced, broad-spectrum filtration of UVB and UVA, the sunscreen formulation must also be chemically photo-stable under UV light when used on human skin, chemically stable in packaging under different conditions, and have negligible transdermal absorption because we need to keep this protection at the surface,” says Dr. Verschoore. The product must also be safe for use in large amounts, non-irritating, user-friendly, invisible and non-staining on the clothes. The cosmetic look of the sunscreen is important so that people apply the proper amount. Finally, it must have an acceptable price for use in large quantities. So how do manufacturers select sunscreen’s active ingredients? It depends on the spectral efficacy. According to Dr. Verschoore, in the United States, only four UVA filters are available: avobenzone (octyl methoxycinnamate), oxybenzone (2-Hydroxy-4-methoxybenzophenone), titanium dioxide and zinc oxide. Of the four, avobenzone, also known as Parsol 1789, is the most efficient. In Europe and other parts of the world, there are new UVA filters, such as Mexoryl SX, Mexoryl XL, Tinosorb S and Tinosorb M, but they have not been approved for use in the US. Titanium dioxide and zinc oxide are preferable UVA/UVB sunscreens because of their efficiency and low irritation. “In many countries, avobenzone has been used in combination with titanium dioxide and zinc oxide to increase the protection in the UVA range,” says Dr. Verschoore. Dramatically increasing the level of an ingredient may not have a corresponding increase in the level of protection. “If you increase the level of zinc oxide, of course you are going to increase the UVA protection, but not a lot,” says Dr. Verschoore. “For example, with 3% of zinc oxide you are going to get a persistent pigment darkening (PPD) of UVA protection around 3, and with 10% you are going to get 4 or 5. So you can see that the difference is not huge.” The efficacy of physical sunscreen, such as zinc oxide, depends on different factors like refractive index, size of particles, dispersion of the formulation and also the film thickness. The refractive index of inorganic pigments is very important to know when formulating a sunscreen. The size of the particles is also important as the smaller the particles, the lower the protection. So, in fact, you have to take into account the ratio, efficacy and cosmetic elements. Also, zinc oxide absorbs more in the UVA range, but titanium dioxide is more efficient in the UVB range. Another important factor is the photo-stabilization of the ingredients used to ensure that the UV protection remains constant. “We need to consider the photo-stability of an ingredient, as some molecules lose their efficacy quickly when exposed to UV radiation and other factors,” says Dr. Verschoore. “Therefore, it is important to photo-stabilize ingredients. The sunscreen formulation is, in fact, a combination of sunscreen solvent and emulsifiers and other agents to improve the photo-resistance.” Evaluation of Product In the United States, the FDA regulates sunscreens, treating them as over-the-counter drugs, and has established standards for labeling sunscreens. In terms of sun protection, sunscreen is measured by its sun protection factor (SPF). A short definition of the SPF, in fact, is a ratio of the minimal erythemal dose on skin protected by the product and the minimal erythemal dose on unprotected skin. There are three categories, SPF 2 to SPF 12 with a minimal sunburn protection, SPF 12 to SPF 30 moderate sunburn protection and above 30 high sunburn protection. “However, you must also be aware of the level of UVA protection provided by the formulation. Two different formulations may provide the same SPF but may provide dramatically different UVA protections,” says Dr. Verschoore. “But how do we evaluate this UVA protection? There are some in-vivo methods like PPD and IPD and some in-vitro methods.” There are a few ways to evaluate UVA protection — in vivo and in vitro. In-vivo methods include PPD and immediate pigment darkening (IPD). The advantages to PPD are that the response is known and stable extending over the whole UVA, the response lasts from 2 hours to 24 hours after irradiation, the law of reciprocity is valid and the method is calibrated. There are some inconveniences because photo type 1 is limited, it uses high UVA doses and it is expensive because of the need for at least 10 subjects. The advantage of the IPD method is that it uses low UV doses. UVA protection evaluation depends on the country. In the United States, there is no official method. In Europe and Japan, they use the PPD. In Australia, they use in-vitro evaluation for broad-spectrum sunscreens. “We would like to see a UVA evaluation and to have a classification according to the SPF/PPD ratio,” says Dr. Verschoore. “Because it makes sense to have high UVA protection when you have the high SPF.” The proposal is to have a ratio above 5 with no UVA protection, a ratio between 4 and 5 with low protection, a ratio between 3 and 4 with normal protection and a ratio of less than 3 with high protection. Application To achieve maximum effectiveness, sunscreens should be applied at least 20 minutes before exposure to the sun and should be reapplied every 2 hours. In addition, sunscreens should also be reapplied after swimming or strenuous activity, even water-resistant sunscreens. Sunscreens should be applied at the rate of 2 milligrams per square centimeter. This translates to roughly 1 ounce of product for each application, more for larger people, less for children. A good rule is to apply two finger lengths to each major body surface. So you would apply two finger lengths to your arms, two lengths to your back, two to your chest and abdomen, two to your upper legs, two to your lower legs and feet. “The FDA does not permit manufacturers to claim all-day protection, since to provide protection, virtually all products have to be reapplied every 2 hours,” says Dr. Verschoore. “Water-resistant formulations must past rigorous testing to determine that they won’t come off when swimming or sweating, but even these should be reapplied after the individual gets wet.” Sunscreen Safety The safety dose for a sunscreen looks like a dose for a drug, for a medical product, because we have to evaluate the acute oral and dermal toxicity, the dermal and high irritation, photo irritation, sensitization, photo sensitization, chronic, oral and topical teratology, fertility, peri- and post-natal toxicity, in-vitro genetic toxicity, photo genetic toxicity in vitro, in-vivo genetic toxicity, and the penetration. “There was a concern a few years ago about the fact if you protect too much you are not able to get your vitamin D. So there were some studies showing, in fact, with good protection, both in UVB and UVA, you are able to have normal vitamin D levels,” says Dr. Verschoore. “In a study, subjects who were protected by sunscreen and people who were not protected had the same level of vitamin D synthesis.” When evaluating sunscreen safety, it is important to evaluate the skin penetration of a product, because the UVA filters must remain on the surface of the skin. According to Dr. Verschoore, studies of the primary UVA filters, oxybenzone, OMC, octocrylene and octyl salicylate, showed that these products remained on the surface of the skin with negligible penetration. A question about the safety of sunscreen in children often arises. “If you consider skin permeability, there is no difference between children and adults,” says Dr. Verschoore. “The susceptibility to irritation is the same for children and adults. But, the major difference for risk assessment is that children have a larger body surface area relative to their body weight.” That means children have a greater exposure to a topically applied penetrating substance than adults. And children have a higher exposure on a body weight basis to UV radiation, and, typically, kids play outside more than adults. That’s why there are some guidelines to evaluate the safety margin for sunscreen. Manufacturers need to consider the amount of formulation that is applied as well as the concentration of each active ingredient in order to be able to evaluate the absorption. Expiration of Sunscreens According to Dr. Verschoore, most sunscreen products remain effective in an unopened container for at least 1 or 2 years, with some companies providing a guarantee of stability for 3 years. However, for the remaining product in an open container, there is no way to determine how long that product will remain stable. The effectiveness of any sunscreen product that has been opened for more than a year may be significantly compromised. You may want to recommend that patients dispose of all products from the previous season that have been opened. Efficacy of Sunscreens Sunscreens can be very effective in protecting the cells of the skin from being modified by UV radiation. For example, in an evaluation study, melanocytes that were UV protected did not change their shapes when exposed to UVA radiation. Those that were unprotected had their shape changed dramatically by UVA radiation. Another study examined the ability of sunscreens to prevent solar urticaria in patients with a history with the condition. Using sunscreen with a SPF of 60 and an UVA protection level of 15, the study showed that the condition could be prevented in these patients with the proper application of sunscreen. Conclusion While UV radiation can have some positive effects, such as vitamin D synthesis, increase in stratum corneum thickness and resistance and anti-inflammatory effects, it also has serious negative effects, including aging of the skin, suppression of the immune system and even cancer. Despite these dangers, many people still do not protect themselves from UV radiation, and those that do often are unaware of how to use sunscreen products correctly to achieve the maximum protection. “A carefully chosen and properly applied sunscreen can protect the wearer from the damage created by UV radiation,” says Dr. Verschoore. “Physicians need to educate their patients about the importance of wearing sunscreen, the need to select the proper sunscreen and how to use and apply sunscreens properly.” Editor’s Note: Henry Lim, M.D., of Detroit, MI, also contributed to this article.
