Cold Plasma in Dermatology: Clinical Uses and Future Directions

Nonthermal atmospheric pressure plasma, or cold plasma, is a technology that can be used to treat a wide range of dermatologic conditions. A partially ionized gas generated by electric devices that interacts with cells and tissues to trigger biologic processes, cold plasma can affect key changes in biologic targets that can be common denominators to treat different diseases, giving it numerous benefits. In cold plasma technologies, the plasma is in energy nonequilibrium and cool enough to be safe on the skin surface. Cold plasmas created under atmospheric pressure conditions are ideal for medical applications.¹ The nature of cold plasma allows for adjustments so it can bedelivered to specific organs, lesions, and conditions using differentdevices, in different ways, with control of the amountdelivered. Cold plasma technologies are currently being usedclinically and in clinical trials. Other cold plasma technologiesare theorized based on animal studies or in vitro experiments.

This review discusses the clinical areas of use for cold plasma in dermatology, practical aspects of cold plasma delivery, studies using cold plasma technology, and future directions and ways of expansion.¹

Clinical Areas of Use
Cold plasma has many uses in dermatology, such as wound healing and regeneration. One well-established use of cold plasma is inhibition of bacteria, which has led to its utilization in treating ulcers. The pathogenesis of ulcers involves bacteria, so reducing the bacterial load can promote healing. Indeed, a clinical trial using argon jet plasma showed a beneficial effect. In addition, floatingelectrode dielectric barrier discharge plasma also reduced bacterial load and ulcer size. Cold plasma is beneficial for healing skin graft donor sites as well, which may be related to plasma’s effect on stem cell differentiation. So far, this has only been demonstrated in nonhuman experiments. Nonetheless, cold plasma exerts a complex influence on several factors that work to improve wound healing and skin function.¹

Other uses of cold plasma in dermatology include its potential to reduce cancer cells, treatment of diseases caused by arthropods, and hair loss treatment. Cold plasma has an antineoplastic effect and can selectively induce cell death in malignant cell lines. Its benefit has been demonstrated in melanoma cells, squamous cell carcinoma cell lines, and actinic keratosis. Cold plasma may be used as a treatment option in diseases caused by arthropods such as head lice—the only single arthropod-caused dermatologic condition currently being targeted for plasma treatment. Hair loss may also be an area in which cold plasma is beneficial. Cold plasma has been shown to influence stem cells by promoting growth and differentiation in various tissues, specifically hair follicle stem cells.¹

Additionally, cold plasma may be used to treat warts, acne, and onychomycosis. Cold plasma destabilizes adenovirus, the virus that causes warts. Adenoviruses are nonenveloped double-stranded DNA viruses, like human papilloma viruses, so cold plasma may have the potential to act on additional viruses. As discussed previously, cold plasma is involved in reducing bacterial load. Acne pathogenesis involves bacteria, making it an ideal target for cold plasma. Onychomycosis, or nail fungal infection, may also be treated with cold plasma. Argon jet plasma has been shown to inhibit several fungal species, including Trichophyton interdigitale, Trichophyton rubrum, Microsporum canis, and Candida albicans.¹

Practical Aspects of Cold Plasma Delivery
Cold plasma delivery can be adapted according to the circumstances in which it is being used and the condition being treated. It is a complex entity made up of free radicals and charged particles, with a composition that changes according to how it was created, UV radiation, and electrified. Cold plasma can be delivered using gas or air and the device settings adjusted to meet specific needs. As a result, the cold plasma effects created with one device cannot be reproduced by another. However, this allows for creating the right amount and composition needed for a specific goal. Because there are so many variables, optimizing treatment conditions requires clinical trials and in vitro studies to evaluate the effects of cold plasma devices and determine how cold plasma exerts its effects on cells and tissues.¹

Both direct and indirect plasma delivery systems can be used. The depth of tissue penetration is important for plasma dosing and is based on factors other than thickness, such as plasma-tissue interactions. Biologic liquids on a treated surface may also affect the depth of penetration. This may change the makeup of cold plasmaderived reactive species that reach the target depth of a treated tissue. Cold plasma should penetrate the entire epidermis, or the superficial dermis at a minimum. In clinical settings, the direct plasma delivery systems plasma jet, dielectric barrier discharge plasma, and surface microdischarge plasma are the most common. Indirect plasma delivery, which entails exposing a liquid to cold plasma and using the liquid to deliver plasma effects, has promise in dermatology. It is currently used for cell culture-based cold plasma experiments.¹

Studies Using Cold Plasma Technology
The complex nature of plasma and its components may raise safety concerns. UV radiation, ozone, nitrogen oxide, and electrical current are components of plasma that already have existing safety standards issued by national regulatory authorities. Other aspects require cold plasma-specific analysis and possibly new safety standard development. Ensuring compliance of the components that already have set safety standards could necessitate measuring values for every cold plasma-specific device. A recent study using a micronucleus assay along with apoptosis assay and hypoxanthine phosphoribosyl transferase (HPRT) gene mutation assay on plasma-treated liver cells found time-dependent micronucleus formation after cold atmospheric plasma exposure. No delayed genomic instability or increased HPRT mutation frequency was found in the target cells or their progeny.²

Several studies demonstrate the safety of cold plasma. When using a jet-type plasma, one study concluded that UV radiation did not penetrate beyond the stratum corneum and the exposure was one order of magnitude lower than that of sun exposure.^2,3 Using an ex vivo model to examine cold plasma device safety, another study analyzed skin specimens that were treated with a surface microdischarge plasma using microscopy, electron microscopy, and a DNA double-strand break assay. No signs of structural changes were found, but an increase of double-strand breaks was observed. However, the cold plasma device was deemed safe and tolerable within the given exposure parameters.^2,4 When examined for mutagenicity, jet-type and dielectric barrier discharge cold plasma devices were found to be safe.^2,5 A study of skin barrier function and skin moisture also found cold plasma was safe and tolerable. Even though many studies show that cold plasma is safe, the presence of reactive species raises a concern for the mutagenicity of cold plasma; every device should be tested.²

Despite many studies showing cold plasma safety, a comprehensive approach is needed for it to be used reliably. The International Organization on Plasma Medical Device Standardization (IOPMS) coordinates efforts for developing plasma safety standards. IOPMS considers device safety according to biomedical safety; physical, technologic, and electric safety; device and treatment protocol; sensitivity to device positioning; dosimetry; and environmental condition safety aspects. The goal of IOPMS is to address concerns applicable to all medical plasma technologies and develop safety standards that regulatory bodies will adopt worldwide.²

Several small studies have been published showing the successful use of cold plasma. For example, to assess the ability of cold plasma to kill Demodex in vivo, a split face study enrolled 3 patients and compared twice a week cold plasma application with daily topical ivermectin. The study showed that cold plasma treatment may reduce the number of Demodex mites on the skin and the treatment is comparable to ivermectin without negative side effects.⁶

In a clinical pilot study, 16 patients with androgenetic alopeciawere enrolled. Four patients were treated using the indirectcold plasma method for 3 months and 10 patients completed 6months of treatment. Findings indicated that the indirect coldplasma treatment was well-tolerated, and most patients reportedimprovement in hair growth.⁷

The first proof-of-concept clinical study of cold plasma treatment of warts demonstrated its efficacy in adult patients using the same dielectric barrier discharge plasma device used for actinic keratosis treatment.8 In a follow-up study, the efficacy and exceptional tolerability of cold plasma to treat warts in children was demonstrated. Five patients with a total of 28 warts on their hands and feet were treated. Treatment sessions were scheduled 4 weeks apart. All lesions were cleared after an average of only 2 treatments. There was no recurrence during the follow-up period, which lasted 6 to 10 months after treatment.⁹

A small case report of 2 patients treated with an argon jet plasma torch device once a week for several weeks found cold plasma to be an effective and well-tolerated treatment for acne based on clinical assessment and related metrics.¹⁰ However, a larger (46 patients) randomized, 2-sided, placebo-controlled study on the efficacy and safety of atmospheric nonthermal argon plasma as an add-on therapy in pruritic diseases showed that the treatment did not result in higher pruritus reduction than treatment with placebo.¹¹ Additional larger studies are needed to determine the efficacy of cold plasma applications in dermatology.

Conclusion and Future Directions
The adaptability of cold plasma makes it ideal for future studies of potential use in many clinical areas. An example of a future area of use is biofilm and the microbiome. Disturbances in the gut microbiome are indicated in several medical conditions and play a role in skin diseases, such as acne, psoriasis, inflammatory hair follicle disorders, and acral melanoma. Reducing the number of bacterial and fungal species on the skin using cold plasma can aid in restoring the microbiome. Arthropod-caused skin disorders, such as scabies and rosacea, may also benefit from indirect cold plasma treatment because it could off er a new antiparasite option. In addition, fine-tuning indirect cold plasma treatment may allow it to be used for skin cancers in vivo. Both the skin cancer mass and the surrounding skin could be contacted using intralesional injections. Cold plasma is well-documented to promote stem cell differentiation and tissue regeneration. Thus, using cold plasma as a tool to reverse aging through its effect on cutaneous stem cells could be a future direction for the technology. This is not only beneficial in cosmetic dermatology, but also in treating degenerative skin diseases.¹

Cold plasma applications have a wide range of potential for the future in dermatology. As devices continue to develop and become standardized, more skin diseases can be targeted. The biggest benefit of cold plasma technology is adjustability, which allows researchers to develop the right treatment for a specific condition.

References
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9. Friedman PC, Fridman G, Fridman A. Using cold plasma to treat warts in children: a case series. Pediatr Dermatol. 2020;37(4):706-709. doi:10.1111/pde.14180

10. Chutsirimongkol C, Boonyawan D, Polnikorn N, Techawatthanawisan W, Kundilokchai T. Non-thermal plasma for acne and aesthetic skin improvement. Plasma Med. 2014;4(1-4):79-88. doi:10.1615/PlasmaMed.2014011952

11. Heinlin J, Isbary G, Stolz W, et al. A randomized two-sided placebo-controlled study on the efficacy and safety of atmospheric non-thermal argon plasma for pruritus. J Eur Acad Dermatol Venereol. 2013;27(3):324-331. doi:10.1111/j.1468-3083.2011.04395.x