Why Photostability Is the Unsung Hero of Summer Sunscreen
Filters that don't break down keep protecting all day.
Bemotrizinol (Parsol Shield) is approved in formulas up to 6% for adults and children 6 months and older.
Bemotrizinol is broad-spectrum and so photostable it retains roughly 98% of activity after intense UV exposure.
Questions we get a lot
Which sunscreen filters are approved in the US vs the EU?
The EU has approved 34 UV filters for sunscreens; the US allows about 16 (now 17 with bemotrizinol's 2026 approval). Filters widely used in Europe and Asia — such as bisoctrizole, drometrizole trisiloxane and Mexoryl 400 — remain under FDA review, which is why US options have lagged.
What does broad-spectrum protection actually mean?
'Broad-spectrum' means a sunscreen protects against both UVA and UVB. In the US a product must pass an FDA critical-wavelength test to make the claim. Because SPF only measures UVB protection, broad-spectrum labeling is how you know you're also covered against deeper, aging UVA rays.
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.
r/AsianBeauty: 'Can someone explain what Tinosorb S and M actually do?'
