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Mexoryl SX

Terephthalylidene Dicamphor Sulfonic AcidSPF filter

Water-soluble UVA filter. Photostable; approved in the US since 2006 in a single brand-licensed formulation.

What it does

Mexoryl SX is a UVA filter with strong photostability. It's water-soluble (most chemical filters are oil-soluble), which makes it well-suited to lightweight aqueous sunscreen formulations. The US FDA approved it specifically for La Roche-Posay's Anthelios formulations in 2006, but it remains rare in US sunscreens because the approval is brand-specific. Standard in EU sunscreens.

The evidence, graded

expert consensusSunscreen must be the final AM step. Applying products on top of sunscreen disrupts the protective film and can compromise the labeled SPF.Petersen 2014 · Photodermatology, Photoimmunology & Photomedicine ↗
expert consensusSPF protection degrades under UV exposure. Reapply sunscreen every 2 hours during continuous sun exposure to maintain rated protection — and immediately after swimming, sweating, or towel-drying.Petersen 2014 · Photodermatology, Photoimmunology & Photomedicine ↗

Graded per the methodology: strong · moderate · emerging · expert consensus. A weak source on a strong claim gets the weaker label.

Also known as

ecamsule, terephthalylidene dicamphor sulfonic acid

Pairs worth knowing

Avobenzone · works together ↗Bemotrizinol · works together ↗

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