Mexoryl SX (Ecamsule)
L'Oréal's patented, water-soluble UVA filter — photostable short-UVA protection found mainly in La Roche-Posay and Vichy
INCITerephthalylidene Dicamphor Sulfonic Acid
- Category
- Sunscreen / UV Filter
- Risk level
- low
- What it covers
- Short-wave UVA (UVA2, ~320–340 nm) — complements long-UVA1 filters like avobenzone and Uvinul A Plus
- Patented + water-soluble
- Developed by L'Oréal (1982); water-soluble (unusual for a chemical filter), so largely exclusive to L'Oréal brands
- Availability
- Approved across the EU/Canada/much of the world; only limited FDA approval in the US (since 2006)
- Tolerability
- 40+ years of use, allergy essentially unheard of
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Possible reactions
- Allergic reactions extremely rare
- No photodegradation
- No sun sensitivity
- Minimal systemic absorption
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What is Mexoryl SX?
Mexoryl SX (INCI: Terephthalylidene Dicamphor Sulfonic Acid; also ecamsule) is a chemical UV filter developed and patented by L'Oréal in 1982 — one of the first modern photostable UVA filters and a cornerstone of premium European sun protection ever since. Unusually for a chemical filter, it's water-soluble, which gives it a distinctive feel and unique formulation options.
It specialises in short-wave UVA (UVA2, ~320–340 nm) — the band between UVB and long UVA1 — so it's combined with long-UVA1 filters (avobenzone, Uvinul A Plus) to round out the spectrum. Because it's patented, it appears almost exclusively in L'Oréal-group brands: La Roche-Posay, Vichy, Garnier. It's approved across the EU, Canada, and much of the world; in the US it has only limited FDA approval (granted 2006 for a few La Roche-Posay products).
Why it's so well tolerated
Over 40+ years of use, Mexoryl SX has an excellent safety record — patch-test contact dermatitis is almost nonexistent, and EU and Health Canada regulators have repeatedly cleared it at cosmetic concentrations.
- Water-soluble — works in light gels and lotions where oil-soluble filters don't.
- Photostable — doesn't degrade and helps stabilise partner filters.
- Minimal absorption — low systemic exposure.
- Family — L'Oréal also makes Mexoryl XL (oil-soluble long-UVA) and Mexoryl 400 (extreme long-UVA, used in Anthelios UVMune 400).
How to use it well
- Look for L'Oréal-group sunscreens — La Roche-Posay Anthelios, Vichy Capital Soleil.
- It's part of a blend — pair (in-formula) with avobenzone/Uvinul A Plus for full UVA.
- Reapply every 2–3 hours outdoors; apply generously.
- A strong choice for melasma and sensitive skin that needs robust, gentle UVA cover.
Alternatives
- Broadly available modern filters: Tinosorb S/M, Uvinul A Plus (across many brands, EU/Asia).
- Most conservative: mineral sunscreens (zinc oxide).
- US users: mineral sunscreens, given Mexoryl's limited FDA status.
The bottom line
Mexoryl SX is a long-proven, water-soluble, photostable UVA2 filter — gentle, low-allergy, and the signature of L'Oréal's well-regarded Anthelios line. Its quirks are commercial and regulatory (patent-exclusive, limited in the US) rather than anything to do with skin safety.
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