How can you determine if a sunscreen is effective against UVA rays?

UVA rays (320 - 400 nm) account for approximately 95% of the UV energy reaching the Earth's surface, while UVB rays (290 - 320 nm) make up the remaining 5%. Although they are not as energetic as UVB rays, UVA rays penetrate deeper into the skin, exerting their maximum effect at the dermis level. Studies associate them with immediate short-term tanning and other long-term damage, whereas they were once considered relatively harmless.

UVA rays are known to generate an excess of reactive oxygen species, which risk indirectly damaging the DNA of skin cells, if they are not quickly neutralized. Although skin cells have antioxidants, DNA repair enzymes, and stress signals to minimize this damage, excessive exposure to UVA rays can lead to mutations and genetic instability. UVA rays are also responsible for premature skin aging (photoaging). Regular exposure to UVA rays can lead to the appearance of deep wrinkles, age spots and a dull complexion.

Furthermore, prolonged exposure to UVA rays can increase the risk of melanoma. They would facilitate the carcinogenesis induced by UVB rays. It has also been demonstrated that exposure to UVA weakens the skin's immune function (photoimmunosuppression), which can make the skin more vulnerable to infections, diseases, and allergic reactions. Indeed, UVA rays would decrease the activity of human epidermal antigen-presenting cells and the number of Langerhans cells. Additionally, this UV-induced immunosuppression likely plays an indirect role in photocarcinogenesis.

Photoprotective measures are therefore widely recommended for everyone, regardless of their skin type. These include wide-brimmed hats and protective clothing, limited exposure to the sun during peak intensity hours (between 11 a.m. and 3 p.m.), and the regular use of sunscreen products with broad-spectrum (UVA/UVB) and a sun protection factor (SPF) of at least 30.

Available since 1928, sunscreen plays a major role in skin cancer prevention and sun protection. The sunscreen industry initially focused on protection against erythemal UV, which is responsible for sunburns, with the introduction of a sun protection factor (SPF). However, in recent years, with the emergence of new research, protection against UVA is now recognized as equally essential and has become a target for improving the effectiveness of sunscreens.

In accordance with new regulations, sun protection products must indicate their UVA protection efficacy, established through in vivo and in vitro tests. The French Agency for the Safety of Health Products (Afssaps) even recommends labeling sun protection products according to the explanatory note published by the European Commission to facilitate readability and guide consumers. This measure aims to ensure that products claiming to protect against UVA, in addition to the SPF, display the "UVA" logo within a circle, assuring that the product complies with European standards for UVA protection.

A sunscreen product that bears thelabel "broad spectrum" is another guarantee that it provides protection against both UVB and UVA rays.

How is the relative UVA protection of sunscreen products evaluated?

Standardized methods in vivo and in vitro have been developed to determine the UVA protection parameters provided by a sunscreen product. These various tests allow us to classify sunscreens into four categories: low, medium, high, and very high UVA protection.

• Photoprotection Test in vivo (ISO 24442:2011): The first test determines the UVA protection factor (PF-UVA). It measures the ability of a sunscreen to prevent tanning, defined as the ratio between the minimum UVA dose required to produce the first pigmentation of the protected skin and that of the unprotected skin. It primarily measures protection against UVA-II (340 - 400 nm).

• Method of UVA Transmission (ISO 24443:2012): Developed by the International Organization for Standardization (ISO), the in vitro test calculates the UVA-I/UVB ratio and is more closely related to the UVA-I (320 - 340 nm) protection provided by sunscreens. This ratio assesses the amount of UVA-I, as well as the amount of UVB, transmitted through a specific glass or plastic plate before and after the application of a sunscreen.

For adequate protection against UVA rays, the UVA-PF must necessarily correspond to at least one third of the SPF indicated on the label, a condition imposed by regulation. Our sun care products have a UVA-PF of 24.9.

• ANANTHASWAMY H. N. & al. Toxic effects of ultraviolet radiation on the skin. Toxicology and Applied Pharmacology (2004).

• COIFFARD L. J. M. & al. In vitro UV-A protection factor (PF-UVA) of organic and inorganic sunscreens. Pharmaceutical Development and Technology (2009).

• COIFFARD L. J. M. & al. Sunscreen products: what do they protect us from? International Journal of Pharmaceutics (2011).

• DAMIAN D. L. & al. Ultraviolet A radiation: its role in immunosuppression and carcinogenesis. Seminars in Cutaneous Medicine and Surgery (2011).

• CHING-SHUANG W. & al. Effects of irradiance on UVA-induced skin aging. Journal of Dermatological Science (2019).