This is a #repost of a blog entry I did a few years back, with a couple of updates. Since I still get this question regularly, it's time for a refresher.
People have a lot of questions (and a lot of confusion) about sunscreen. For this post, I thought I'd tackle UVA and UVB. There is some great in-depth information here from skincancer.org, but here are some key points.
- Think A for "aging".
- UVA penetrates the skin deeply and plays a big role in photo-aging the skin and causing wrinkles.
- The strength of UVA rays is consistent throughout the day, penetrates cloud cover, and glass.
- Mainly responsible for tanning.
- The words "broad spectrum" are your only guide to knowing if your sunscreen protects you from UVA. The FDA monograph will be updated in 2021. Hopefully, an easy-to-understand rating system for UVA will make it in this time.
- Think B for "burning".
- UVB is responsible for damaging the superficial layers of the skin and causing redness and sunburn.
- Reflective surfaces like water, snow, and ice can create a "bounce-back" effect - multiplying the amount of UV radiation that hits the skin.
- UVB is strongest in the US from April to October, between 10am and 4pm, but can burn skin year-round - especially at high altitudes.
- The "SPF" rating on your sunscreen ONLY applies to UVB and refers to extending the length of time it would take for the skin to first show signs of redness, it does not refer to UVA protection.