It is widely believed that ultraviolet A (UVA) radiation, which penetrates deeper into the skin than ultraviolet B (UVB), contributes to many of the harmful effects of sun exposure.
New research into the science of sun protection and the effects of UV radiation on skin has led to the development of unique new sun protection agents as well as new strategies to help prevent and repair photodamage.
Research has also increased our understanding of the different effects of UV radiation in different ethnicities and skin phototypes and has enhanced our appreciation of populations at risk for skin cancers.
UVA VS. UVB Radiation
Initially, because exposure to higher-energy UVB radiation causes visible burning within minutes or hours of sun exposure, it appeared to be more deleterious than UVA radiation. However, recommendations from a 2000 consensus conference on UVA protection noted that UVA appears to play a greater role in long-term sun damage than in acute damage.1 This was attributed to the following facts: nearly 20 times more UVA than UVB reaches the Earth; UVA is not filtered by window glass and has little temporal flux attenuation; UVA is relatively unaffected by altitude or atmospheric conditions; UVA is present all day and throughout the year; and it penetrates deeply into the dermis, the site of many changes associated with photoaging.1
UVA interacts with DNA less strongly than does UVB but has indirect effects on DNA that are mediated through the formation of reactive oxygen species (ROS). (See Table)1,2,3 UVB penetrates less deeply but is capable of generating DNA photoproducts at all levels of the epidermis.2 Recently, it has been shown that both UVA and UVB generate highly mutagenic pyrimidine dimers.4 Lastly, studies have shown that both UVA and UVB are immunosuppressive.5
Countering These Effects
Increasing appreciation of the contributions of both UVA and UVB to photoaging and photocarcinogenesis has emphasized the need for new generations of broad-spectrum sunscreen formulations as well as other clinical strategies aimed at providing complete protection to the skin.
Need for Photoprotection Among all Skin Types
Along with increasing understanding of the contribution of UVA to photodamage and photocarcinogenesis has come a better understanding of the need for photoprotection in all skin types.
Skin of Color Concerns
A 1979 study suggested that the epidermis of black skin has a sun protection factor of 13.4 versus 3.4 for lighter-skinned individuals.6 These data, coupled with the evidence of a lower risk of photocarcinogenesis and less obvious photodamage in darker skin types, led to the assumption by both physicians and patients that skin of color did not require sun protection.7 However, it has been demonstrated recently that the issue is more complex. A study by Sheehan and colleagues found that the sun protection afforded by Fitzpatrick skin types II and IV were both approximately 2 to 3 but that type IV skin was better able to repair thymine dimers.8 It has been suggested that it is the capacity for DNA repair rather than the constitutive level of melanization that likely accounts for the lower incidence of skin cancers in black skin.9
A recent study demonstrated that UV radiation during the summer months leads to a clear overexpression of melanin in African American skin.10 Solar exposure sufficient to increase pigmentation in darker complexions may produce other damaging effects at the basal keratinocyte level, including DNA damage, cellular apoptosis, and immunosuppression. Although these effects may not occur to the same extent as in Caucasian skin, they are not negligible. In this 8-week study of daily use of a photostabilized sunscreen by African American patients with hyperpigmentation on the face and at least one hyperpigmented lesion on one arm, mexameter measurements for pigmentation showed significantly decreased melanin values in both the hyperpigmented areas and the surrounding skin (p<0.05) versus baseline. Dermatologist assessment showed improvements from baseline in hyperpigmentation and overall skin tone and texture after 4 and 8 weeks of sunscreen use.10
The cutaneous stigmata of photoaging are much less evident in darker skin. Rather than wrinkles and sagging skin, which are common in photoaged skin of Caucasians, photoaging in black skin is more typically evidenced by pigmentary anomalies.7 In addition, melasma and postinflammatory hyperpigmentation are more common in darker skin types, are exacerbated by sun exposure, and can be reduced by the use of sunscreens.7
Immunosuppression
Few patients are aware that UV exposure also induces both local and systemic immunosuppression and that its prevention is important for all skin types. Acute low-dose UVB exposure impairs the induction of contact hypersensitivity in approximately 40% of Caucasians but virtually 100% of patients with biopsy-proven skin cancers.11 It has been demonstrated that low-dose UVB radiation leads to Langerhans cell depletion equally in black and in white skin. Melanin does not appear to protect against this cutaneous immunosuppression.11
Skin Cancer and Skin of Color
The lifetime risk in 2003 of developing invasive malignant melanoma (MM) was approximately 1 in 67.12 At present, in the United States, MNNNNc, the lifetime risk for developing nonmelanoma skin cancer, is 1 in 5.13
Individuals of color appeared to be relatively protected. Between 2000 and 2004, the ratio of MM was 1 to 25 in black versus white skin.14 Unfortunately, it is now clear that MM is as dangerous in more deeply pigmented skin types as it is in Caucasian skin types I to II,15 although the presentation is frequently different. The sole of the foot, palms, and subungal and mucosal surfaces have been shown to be the most common sites for MM in African Americans.16
Perhaps partly because of a lack of concern about cancers in darker skins, the unusual locations of these MM lesions, and the risk of mistaking the lesions for normal pigmentary variations, African Americans with MM have been shown to present at a later, less curable stage of the disease, which has significant impact on survival. In one study, the 5-year survival rates for white and black patients were 84.8% and 58.8%, respectively.17
Prevention of Photoaging
Although numerous treatments and products that aim to repair photodamage are available and play an integral role in skin health, the simplest and most effective measure is prevention through the use of sunscreens and sun avoidance measures ranging from staying indoors at peak hours, wearing sun-protective clothing, and installing UV-blocking glass in homes and cars.
Sunscreen Issues
Many patients claim they tan despite faithful application of high-SPF sunscreens. Although they frequently apply less sunscreen than is recommended for protection, it is now clear that another large issue has been sunscreen formulations with inadequate absorption of UVA radiation as well as filters with inadequate photostability.
Sunscreens enhance the body’s endogenous photoprotection systems.2 Inorganic sunscreens, such as zinc oxide and titanium dioxide, act as physical blocks that scatter light, whereas organic or chemical sunscreens absorb UV energy and transform it to heat within the skin.18
The photostability of organic sunscreens is key to their efficacy.2 A photostable filter continues to protect the skin after it absorbs and transforms UV radiation, because rather than being degraded, it returns to its ground state where it is capable of absorbing more UV radiation.18
In contrast, physical filters that reflect or scatter the majority of UV radiation have a greater life span on the skin surface.2 However, aesthetic concerns complicate the use of physical filters, since they typically leave a white residue on the skin when they contain particles that are sufficiently large to offer good photoprotection. Both zinc oxide and titanium dioxide can be micronized for improved aesthetics. A particle size of ~ 0.1 micron is the most effective. The ability to block UV decreases as particle size decreases below 0.1 micron, yet particles larger than this can cause visible whitening.19
Technologic Advances
Technologic advances have now permitted the development of broad-spectrum, photostable sunscreens with better UVA protection.
Broad-spectrum photoprotection from both organic and inorganic filters depends on combining different filters according to their peak absorption spectra.20
Oxybenzone is a commonly used filter that provides only weak protection against UVA, whereas avobenzone (Parsol 1789) provides excellent UVA protection but is highly unstable after UV exposure.2 A recent innovation has been the combination of oxybenzone and avobenzone, which has been photostabilized with the solvent diethylhexyl 2,6-naphthalate, known commercially as Corapan TQ.
Figure 1 demonstrates the transfer of energy and heat from the avobenzone to the diethylhexyl 2,6-naphthalate, and Figure 2 shows the extended photoprotection that is achievable with this formulation in contrast to a nonphotostabilized formulation after 5 hours of simulated solar exposure.22
In one study, comparing free radical counts generated in the skin from UVA radiation, the site to which the photostable sunscreen formulation had been applied showed a 76% reduction in free-radical counts compared to a 32% reduction at a site where a non-photostable sunscreen had been applied.23
Recently, a sunscreen formulation containing oxybenzone, photostabilized avobenzone, and the UVB filters octisalate, homosalate, and octocrylene has become available. This formulation also contains vitamins C and E, both physiologic antioxidants in humans.
Antioxidants confer an additional level of photoprotection by adding to the skin’s natural antioxidant reservoir to increase protection against free-radical damage, including inflammation and the induction of mitogen-activated protein kinases.24
Another new approach is ecamsule, a photostable short UVA filter that has been used for many years throughout the world and was approved in July 2006 by the U.S. Food and Drug Administration. Ecamsule is a UVA filter with a peak absorbance around 345 nm, with limited absorbance beyond 370 nm, but when combined with other filters, ecamsule can help to increase the overall photoprotection of a formula. A new product consisting of avobenzone stabilized with octocrylene, a photostable UVB filter, plus ecamsule in a moisturizing base is now available.
Conclusion
The increased appreciation of the harmful effects of UVA radiation has been paralleled by the development of improved UVA filters and new technology to photostabilize them. These advances have led to a new generation of sunscreens that are photostable, thus providing more longer-lasting protection than was achievable with earlier generations of sunscreens. In addition, new combinations of filters provide improved broad-spectrum photoprotection. The addition of a variety of natural ingredients to confer additional antioxidant protection against free radical damage further enhances the utility of these formulations in protecting against skin cancers and photoaging.
It is widely believed that ultraviolet A (UVA) radiation, which penetrates deeper into the skin than ultraviolet B (UVB), contributes to many of the harmful effects of sun exposure.
New research into the science of sun protection and the effects of UV radiation on skin has led to the development of unique new sun protection agents as well as new strategies to help prevent and repair photodamage.
Research has also increased our understanding of the different effects of UV radiation in different ethnicities and skin phototypes and has enhanced our appreciation of populations at risk for skin cancers.
UVA VS. UVB Radiation
Initially, because exposure to higher-energy UVB radiation causes visible burning within minutes or hours of sun exposure, it appeared to be more deleterious than UVA radiation. However, recommendations from a 2000 consensus conference on UVA protection noted that UVA appears to play a greater role in long-term sun damage than in acute damage.1 This was attributed to the following facts: nearly 20 times more UVA than UVB reaches the Earth; UVA is not filtered by window glass and has little temporal flux attenuation; UVA is relatively unaffected by altitude or atmospheric conditions; UVA is present all day and throughout the year; and it penetrates deeply into the dermis, the site of many changes associated with photoaging.1
UVA interacts with DNA less strongly than does UVB but has indirect effects on DNA that are mediated through the formation of reactive oxygen species (ROS). (See Table)1,2,3 UVB penetrates less deeply but is capable of generating DNA photoproducts at all levels of the epidermis.2 Recently, it has been shown that both UVA and UVB generate highly mutagenic pyrimidine dimers.4 Lastly, studies have shown that both UVA and UVB are immunosuppressive.5
Countering These Effects
Increasing appreciation of the contributions of both UVA and UVB to photoaging and photocarcinogenesis has emphasized the need for new generations of broad-spectrum sunscreen formulations as well as other clinical strategies aimed at providing complete protection to the skin.
Need for Photoprotection Among all Skin Types
Along with increasing understanding of the contribution of UVA to photodamage and photocarcinogenesis has come a better understanding of the need for photoprotection in all skin types.
Skin of Color Concerns
A 1979 study suggested that the epidermis of black skin has a sun protection factor of 13.4 versus 3.4 for lighter-skinned individuals.6 These data, coupled with the evidence of a lower risk of photocarcinogenesis and less obvious photodamage in darker skin types, led to the assumption by both physicians and patients that skin of color did not require sun protection.7 However, it has been demonstrated recently that the issue is more complex. A study by Sheehan and colleagues found that the sun protection afforded by Fitzpatrick skin types II and IV were both approximately 2 to 3 but that type IV skin was better able to repair thymine dimers.8 It has been suggested that it is the capacity for DNA repair rather than the constitutive level of melanization that likely accounts for the lower incidence of skin cancers in black skin.9
A recent study demonstrated that UV radiation during the summer months leads to a clear overexpression of melanin in African American skin.10 Solar exposure sufficient to increase pigmentation in darker complexions may produce other damaging effects at the basal keratinocyte level, including DNA damage, cellular apoptosis, and immunosuppression. Although these effects may not occur to the same extent as in Caucasian skin, they are not negligible. In this 8-week study of daily use of a photostabilized sunscreen by African American patients with hyperpigmentation on the face and at least one hyperpigmented lesion on one arm, mexameter measurements for pigmentation showed significantly decreased melanin values in both the hyperpigmented areas and the surrounding skin (p<0.05) versus baseline. Dermatologist assessment showed improvements from baseline in hyperpigmentation and overall skin tone and texture after 4 and 8 weeks of sunscreen use.10
The cutaneous stigmata of photoaging are much less evident in darker skin. Rather than wrinkles and sagging skin, which are common in photoaged skin of Caucasians, photoaging in black skin is more typically evidenced by pigmentary anomalies.7 In addition, melasma and postinflammatory hyperpigmentation are more common in darker skin types, are exacerbated by sun exposure, and can be reduced by the use of sunscreens.7
Immunosuppression
Few patients are aware that UV exposure also induces both local and systemic immunosuppression and that its prevention is important for all skin types. Acute low-dose UVB exposure impairs the induction of contact hypersensitivity in approximately 40% of Caucasians but virtually 100% of patients with biopsy-proven skin cancers.11 It has been demonstrated that low-dose UVB radiation leads to Langerhans cell depletion equally in black and in white skin. Melanin does not appear to protect against this cutaneous immunosuppression.11
Skin Cancer and Skin of Color
The lifetime risk in 2003 of developing invasive malignant melanoma (MM) was approximately 1 in 67.12 At present, in the United States, MNNNNc, the lifetime risk for developing nonmelanoma skin cancer, is 1 in 5.13
Individuals of color appeared to be relatively protected. Between 2000 and 2004, the ratio of MM was 1 to 25 in black versus white skin.14 Unfortunately, it is now clear that MM is as dangerous in more deeply pigmented skin types as it is in Caucasian skin types I to II,15 although the presentation is frequently different. The sole of the foot, palms, and subungal and mucosal surfaces have been shown to be the most common sites for MM in African Americans.16
Perhaps partly because of a lack of concern about cancers in darker skins, the unusual locations of these MM lesions, and the risk of mistaking the lesions for normal pigmentary variations, African Americans with MM have been shown to present at a later, less curable stage of the disease, which has significant impact on survival. In one study, the 5-year survival rates for white and black patients were 84.8% and 58.8%, respectively.17
Prevention of Photoaging
Although numerous treatments and products that aim to repair photodamage are available and play an integral role in skin health, the simplest and most effective measure is prevention through the use of sunscreens and sun avoidance measures ranging from staying indoors at peak hours, wearing sun-protective clothing, and installing UV-blocking glass in homes and cars.
Sunscreen Issues
Many patients claim they tan despite faithful application of high-SPF sunscreens. Although they frequently apply less sunscreen than is recommended for protection, it is now clear that another large issue has been sunscreen formulations with inadequate absorption of UVA radiation as well as filters with inadequate photostability.
Sunscreens enhance the body’s endogenous photoprotection systems.2 Inorganic sunscreens, such as zinc oxide and titanium dioxide, act as physical blocks that scatter light, whereas organic or chemical sunscreens absorb UV energy and transform it to heat within the skin.18
The photostability of organic sunscreens is key to their efficacy.2 A photostable filter continues to protect the skin after it absorbs and transforms UV radiation, because rather than being degraded, it returns to its ground state where it is capable of absorbing more UV radiation.18
In contrast, physical filters that reflect or scatter the majority of UV radiation have a greater life span on the skin surface.2 However, aesthetic concerns complicate the use of physical filters, since they typically leave a white residue on the skin when they contain particles that are sufficiently large to offer good photoprotection. Both zinc oxide and titanium dioxide can be micronized for improved aesthetics. A particle size of ~ 0.1 micron is the most effective. The ability to block UV decreases as particle size decreases below 0.1 micron, yet particles larger than this can cause visible whitening.19
Technologic Advances
Technologic advances have now permitted the development of broad-spectrum, photostable sunscreens with better UVA protection.
Broad-spectrum photoprotection from both organic and inorganic filters depends on combining different filters according to their peak absorption spectra.20
Oxybenzone is a commonly used filter that provides only weak protection against UVA, whereas avobenzone (Parsol 1789) provides excellent UVA protection but is highly unstable after UV exposure.2 A recent innovation has been the combination of oxybenzone and avobenzone, which has been photostabilized with the solvent diethylhexyl 2,6-naphthalate, known commercially as Corapan TQ.
Figure 1 demonstrates the transfer of energy and heat from the avobenzone to the diethylhexyl 2,6-naphthalate, and Figure 2 shows the extended photoprotection that is achievable with this formulation in contrast to a nonphotostabilized formulation after 5 hours of simulated solar exposure.22
In one study, comparing free radical counts generated in the skin from UVA radiation, the site to which the photostable sunscreen formulation had been applied showed a 76% reduction in free-radical counts compared to a 32% reduction at a site where a non-photostable sunscreen had been applied.23
Recently, a sunscreen formulation containing oxybenzone, photostabilized avobenzone, and the UVB filters octisalate, homosalate, and octocrylene has become available. This formulation also contains vitamins C and E, both physiologic antioxidants in humans.
Antioxidants confer an additional level of photoprotection by adding to the skin’s natural antioxidant reservoir to increase protection against free-radical damage, including inflammation and the induction of mitogen-activated protein kinases.24
Another new approach is ecamsule, a photostable short UVA filter that has been used for many years throughout the world and was approved in July 2006 by the U.S. Food and Drug Administration. Ecamsule is a UVA filter with a peak absorbance around 345 nm, with limited absorbance beyond 370 nm, but when combined with other filters, ecamsule can help to increase the overall photoprotection of a formula. A new product consisting of avobenzone stabilized with octocrylene, a photostable UVB filter, plus ecamsule in a moisturizing base is now available.
Conclusion
The increased appreciation of the harmful effects of UVA radiation has been paralleled by the development of improved UVA filters and new technology to photostabilize them. These advances have led to a new generation of sunscreens that are photostable, thus providing more longer-lasting protection than was achievable with earlier generations of sunscreens. In addition, new combinations of filters provide improved broad-spectrum photoprotection. The addition of a variety of natural ingredients to confer additional antioxidant protection against free radical damage further enhances the utility of these formulations in protecting against skin cancers and photoaging.
It is widely believed that ultraviolet A (UVA) radiation, which penetrates deeper into the skin than ultraviolet B (UVB), contributes to many of the harmful effects of sun exposure.
New research into the science of sun protection and the effects of UV radiation on skin has led to the development of unique new sun protection agents as well as new strategies to help prevent and repair photodamage.
Research has also increased our understanding of the different effects of UV radiation in different ethnicities and skin phototypes and has enhanced our appreciation of populations at risk for skin cancers.
UVA VS. UVB Radiation
Initially, because exposure to higher-energy UVB radiation causes visible burning within minutes or hours of sun exposure, it appeared to be more deleterious than UVA radiation. However, recommendations from a 2000 consensus conference on UVA protection noted that UVA appears to play a greater role in long-term sun damage than in acute damage.1 This was attributed to the following facts: nearly 20 times more UVA than UVB reaches the Earth; UVA is not filtered by window glass and has little temporal flux attenuation; UVA is relatively unaffected by altitude or atmospheric conditions; UVA is present all day and throughout the year; and it penetrates deeply into the dermis, the site of many changes associated with photoaging.1
UVA interacts with DNA less strongly than does UVB but has indirect effects on DNA that are mediated through the formation of reactive oxygen species (ROS). (See Table)1,2,3 UVB penetrates less deeply but is capable of generating DNA photoproducts at all levels of the epidermis.2 Recently, it has been shown that both UVA and UVB generate highly mutagenic pyrimidine dimers.4 Lastly, studies have shown that both UVA and UVB are immunosuppressive.5
Countering These Effects
Increasing appreciation of the contributions of both UVA and UVB to photoaging and photocarcinogenesis has emphasized the need for new generations of broad-spectrum sunscreen formulations as well as other clinical strategies aimed at providing complete protection to the skin.
Need for Photoprotection Among all Skin Types
Along with increasing understanding of the contribution of UVA to photodamage and photocarcinogenesis has come a better understanding of the need for photoprotection in all skin types.
Skin of Color Concerns
A 1979 study suggested that the epidermis of black skin has a sun protection factor of 13.4 versus 3.4 for lighter-skinned individuals.6 These data, coupled with the evidence of a lower risk of photocarcinogenesis and less obvious photodamage in darker skin types, led to the assumption by both physicians and patients that skin of color did not require sun protection.7 However, it has been demonstrated recently that the issue is more complex. A study by Sheehan and colleagues found that the sun protection afforded by Fitzpatrick skin types II and IV were both approximately 2 to 3 but that type IV skin was better able to repair thymine dimers.8 It has been suggested that it is the capacity for DNA repair rather than the constitutive level of melanization that likely accounts for the lower incidence of skin cancers in black skin.9
A recent study demonstrated that UV radiation during the summer months leads to a clear overexpression of melanin in African American skin.10 Solar exposure sufficient to increase pigmentation in darker complexions may produce other damaging effects at the basal keratinocyte level, including DNA damage, cellular apoptosis, and immunosuppression. Although these effects may not occur to the same extent as in Caucasian skin, they are not negligible. In this 8-week study of daily use of a photostabilized sunscreen by African American patients with hyperpigmentation on the face and at least one hyperpigmented lesion on one arm, mexameter measurements for pigmentation showed significantly decreased melanin values in both the hyperpigmented areas and the surrounding skin (p<0.05) versus baseline. Dermatologist assessment showed improvements from baseline in hyperpigmentation and overall skin tone and texture after 4 and 8 weeks of sunscreen use.10
The cutaneous stigmata of photoaging are much less evident in darker skin. Rather than wrinkles and sagging skin, which are common in photoaged skin of Caucasians, photoaging in black skin is more typically evidenced by pigmentary anomalies.7 In addition, melasma and postinflammatory hyperpigmentation are more common in darker skin types, are exacerbated by sun exposure, and can be reduced by the use of sunscreens.7
Immunosuppression
Few patients are aware that UV exposure also induces both local and systemic immunosuppression and that its prevention is important for all skin types. Acute low-dose UVB exposure impairs the induction of contact hypersensitivity in approximately 40% of Caucasians but virtually 100% of patients with biopsy-proven skin cancers.11 It has been demonstrated that low-dose UVB radiation leads to Langerhans cell depletion equally in black and in white skin. Melanin does not appear to protect against this cutaneous immunosuppression.11
Skin Cancer and Skin of Color
The lifetime risk in 2003 of developing invasive malignant melanoma (MM) was approximately 1 in 67.12 At present, in the United States, MNNNNc, the lifetime risk for developing nonmelanoma skin cancer, is 1 in 5.13
Individuals of color appeared to be relatively protected. Between 2000 and 2004, the ratio of MM was 1 to 25 in black versus white skin.14 Unfortunately, it is now clear that MM is as dangerous in more deeply pigmented skin types as it is in Caucasian skin types I to II,15 although the presentation is frequently different. The sole of the foot, palms, and subungal and mucosal surfaces have been shown to be the most common sites for MM in African Americans.16
Perhaps partly because of a lack of concern about cancers in darker skins, the unusual locations of these MM lesions, and the risk of mistaking the lesions for normal pigmentary variations, African Americans with MM have been shown to present at a later, less curable stage of the disease, which has significant impact on survival. In one study, the 5-year survival rates for white and black patients were 84.8% and 58.8%, respectively.17
Prevention of Photoaging
Although numerous treatments and products that aim to repair photodamage are available and play an integral role in skin health, the simplest and most effective measure is prevention through the use of sunscreens and sun avoidance measures ranging from staying indoors at peak hours, wearing sun-protective clothing, and installing UV-blocking glass in homes and cars.
Sunscreen Issues
Many patients claim they tan despite faithful application of high-SPF sunscreens. Although they frequently apply less sunscreen than is recommended for protection, it is now clear that another large issue has been sunscreen formulations with inadequate absorption of UVA radiation as well as filters with inadequate photostability.
Sunscreens enhance the body’s endogenous photoprotection systems.2 Inorganic sunscreens, such as zinc oxide and titanium dioxide, act as physical blocks that scatter light, whereas organic or chemical sunscreens absorb UV energy and transform it to heat within the skin.18
The photostability of organic sunscreens is key to their efficacy.2 A photostable filter continues to protect the skin after it absorbs and transforms UV radiation, because rather than being degraded, it returns to its ground state where it is capable of absorbing more UV radiation.18
In contrast, physical filters that reflect or scatter the majority of UV radiation have a greater life span on the skin surface.2 However, aesthetic concerns complicate the use of physical filters, since they typically leave a white residue on the skin when they contain particles that are sufficiently large to offer good photoprotection. Both zinc oxide and titanium dioxide can be micronized for improved aesthetics. A particle size of ~ 0.1 micron is the most effective. The ability to block UV decreases as particle size decreases below 0.1 micron, yet particles larger than this can cause visible whitening.19
Technologic Advances
Technologic advances have now permitted the development of broad-spectrum, photostable sunscreens with better UVA protection.
Broad-spectrum photoprotection from both organic and inorganic filters depends on combining different filters according to their peak absorption spectra.20
Oxybenzone is a commonly used filter that provides only weak protection against UVA, whereas avobenzone (Parsol 1789) provides excellent UVA protection but is highly unstable after UV exposure.2 A recent innovation has been the combination of oxybenzone and avobenzone, which has been photostabilized with the solvent diethylhexyl 2,6-naphthalate, known commercially as Corapan TQ.
Figure 1 demonstrates the transfer of energy and heat from the avobenzone to the diethylhexyl 2,6-naphthalate, and Figure 2 shows the extended photoprotection that is achievable with this formulation in contrast to a nonphotostabilized formulation after 5 hours of simulated solar exposure.22
In one study, comparing free radical counts generated in the skin from UVA radiation, the site to which the photostable sunscreen formulation had been applied showed a 76% reduction in free-radical counts compared to a 32% reduction at a site where a non-photostable sunscreen had been applied.23
Recently, a sunscreen formulation containing oxybenzone, photostabilized avobenzone, and the UVB filters octisalate, homosalate, and octocrylene has become available. This formulation also contains vitamins C and E, both physiologic antioxidants in humans.
Antioxidants confer an additional level of photoprotection by adding to the skin’s natural antioxidant reservoir to increase protection against free-radical damage, including inflammation and the induction of mitogen-activated protein kinases.24
Another new approach is ecamsule, a photostable short UVA filter that has been used for many years throughout the world and was approved in July 2006 by the U.S. Food and Drug Administration. Ecamsule is a UVA filter with a peak absorbance around 345 nm, with limited absorbance beyond 370 nm, but when combined with other filters, ecamsule can help to increase the overall photoprotection of a formula. A new product consisting of avobenzone stabilized with octocrylene, a photostable UVB filter, plus ecamsule in a moisturizing base is now available.
Conclusion
The increased appreciation of the harmful effects of UVA radiation has been paralleled by the development of improved UVA filters and new technology to photostabilize them. These advances have led to a new generation of sunscreens that are photostable, thus providing more longer-lasting protection than was achievable with earlier generations of sunscreens. In addition, new combinations of filters provide improved broad-spectrum photoprotection. The addition of a variety of natural ingredients to confer additional antioxidant protection against free radical damage further enhances the utility of these formulations in protecting against skin cancers and photoaging.
