A simple way to remember the difference is: UVA = UV-Aging, whereas UVB = UV-Burning. In truth, both contribute to aging and burning, but the short-wavelength surface burning effects of UVB rays are seen much sooner than the aging effects of long-wavelength deeper-penetrating UVA rays (Cosmetic Dermatology, 2009), so this acronym works.
UVA rays are longer and have been found to play a role in skin cancer and premature signs of skin aging (Journal of the American Academy of Dermatology, 1995; Journal of Investigative Dermatology, 1995). When UVA is rated, it is generally rated with a star system, where one star is low protection and 5 is superior protection.
On the other hand, UVB rays cause immediate skin erythema (skin burning). SPF ratings were developed to measure UVB protection and not UVA, signs of which take much longer to appear. SPF is specifically the level of sun exposure needed to produce a minimal skin erythema (skin reddening) divided by the amount of energy required to produce the same erythema on unprotected skin. In theory, a subject that applies SPF 10 could stay in the sun 10 times longer without incurring skin redness (Cosmetic Dermatology, 2009).
Sunscreen ingredients matter
Some of our favorite UVA/UVB sunscreens include the following:
- Homosalate may help limit inflammation, resulting in reduced redness in the skin (European Journal of Pharmacology). It’s also so effective that it is one of the active ingredients in the standard sunscreen formulation the FDA uses to test the SPF of other sunscreens (FDA).
- Avobenzone is a very common sunscreen ingredient. It works by taking UV light and converting it into energy that isn’t harmful. Avobenzone protects moderately well against both UVA and UVB rays.
- Octisalate is a photostabilizer used to reduce the degradation of avobenzone (JAAD).
- Octocrylene is an avobenzone stabilizer that provides further UVB protection (Free Radical Research, 2010).
What You Can Do About It