In addition, sunscreen efficacy decreases in the water or with sweating. To help consumers, FDA now requires sunscreens labeled “water-resistant” or “very water-resistant” to last up to 40 minutes or 80 minutes, respectively, in the water, and the American Academy of Dermatology and other medical professional groups recommend reapplication immediately after any water sports. The general rule of thumb is to reapply about every two hours and certainly after water sports or sweating.
To get high SPF values, multiple UVB UV filters are combined into a formulation based upon safety standards set by the FDA. However, the SPF doesn’t account for UVA protection. For a sunscreen to make a claim as having UVA and UVB protection and be labeled “Broad Spectrum,” it must pass FDA’s Broad Spectrum Test, where the sunscreen is hit with a large dose of UVB and UVA light before its effectiveness is tested.
This pre-irradiation step was established in FDA’s 2012 sunscreen labeling rules and acknowledges something significant about UV-filters: some can be photolabile, meaning they can degrade under UV irradiation. The most famous example may be PABA. This UVB-absorbing molecule is rarely used in sunscreens today because it forms photoproducts that elicit an allergic reaction in some people.
But the Broad Spectrum Test really came into effect only once the UVA-absorbing molecule avobenzone came onto the market. Avobenzone can interact with octinoxate, a strong and widely used UVB absorber, in a way that makes avobenzone less effective against UVA photons. The UVB filter octocrylene, on the other hand, helps stabilize avobenzone so it lasts longer in its UVA-absorbing form. Additionally, you may notice on some sunscreen labels the molecule ethylhexyl methoxycrylene. It helps stabilize avobenzone even in the presence of octinoxate, and provides us with longer-lasting protection against UVA rays.
Next up in sunscreen innovation is the broadening of their mission. Because even the highest SPF sunscreens don’t block 100 percent of UV rays, the addition of antioxidants can supply a second line of protection when the skin’s natural antioxidant defenses are overloaded. Some antioxidant ingredients my colleagues and I have worked with include tocopheral acetate (Vitamin E), sodium ascorbyl phosophate (Vitamin C), and DESM. And sunscreen researchers are beginning to investigate if the absorption of other colors of light, like infrared, by skin molecules has a role to play in photodamage.
As research continues, one thing we know for certain is that protecting our DNA from UV damage, for people of every color, is synonymous with preventing skin cancers. The Skin Cancer Foundation, American Cancer Society and the American Academy of Dermatology all stress that research shows regular use of an SPF 15 or higher sunscreen prevents sunburn and reduces the risk of non-melanoma cancers by 40 percent and melanoma by 50 percent.
We can still enjoy being in the sun. Unlike my Aunt Muriel and us kids in the 1980s, we just need to use the resources available to us, from long sleeves to shade to sunscreens, in order to protect the molecules in our skin, especially our DNA, from UV damage.
Kerry Hanson, Research Chemist, University of California, Riverside
This article is republished from The Conversation under a Creative Commons license. Read the original article.