What 'Photostable' Actually Means on a Sunscreen Label
Not all filters survive the sun they're supposed to block.
Zinc/titanium agglomerates of ~0.1-10 μm scatter visible light, producing the white-cast effect.
Avobenzone is often paired with octocrylene to keep it from degrading in sunlight.
Frequently asked questions
Do antioxidants in sunscreen actually work?
Antioxidants such as vitamins C and E don't filter UV, but they can neutralize some of the free radicals UV generates, adding a complementary layer of defense. They support — never replace — sunscreen. A studied vitamin C+E combination showed measurable added photoprotection.
Why are some UV filters more photostable?
A photostable filter keeps absorbing UV without breaking down in sunlight. Older filters like avobenzone can lose protection within an hour unless paired with stabilizers such as octocrylene. Next-generation filters are engineered to stay chemically stable, so protection lasts longer — though reapplication is still advised.
What is the difference between nano and non-nano zinc?
Nano zinc has smaller particles, so it rubs in more clearly with less white cast; non-nano uses larger particles that scatter more visible light but are preferred by some for environmental or personal reasons. Current evidence indicates nanoparticles in sunscreen don't penetrate healthy skin.
r/AsianBeauty: 'Do antioxidants in sunscreen actually do anything?'
Sources & citations
- 'A standardized scoring method for measuring white cast of mineral sunscreens,' PMC12380271
- sciencedirect.com ↗