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Sunscreen filters

Octocrylene

Also listed as OCR, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate

UVB filter mostly used to stabilise avobenzone. Effective, but can break down to benzophenone in the bottle and occasionally causes photoallergy.

Strong evidenceTypical strength: Up to 10% (US and EU; EU 9% in propellant sprays)

What it is

Octocrylene absorbs UVB and short-wave UVA2 and, just as important, it stabilises avobenzone so the UVA protection lasts in sunlight. It also helps dissolve other filters.

Two things put it under scrutiny. Lab work found that it slowly degrades to benzophenone (a suspected carcinogen) in the bottle, rising as products age. And it is a known, if uncommon, cause of photoallergic rashes.

How strong is the evidence?

Strong evidence

Its UV absorption and stabilising role are well established in formulation testing and SPF measurement. It is absorbed into the blood (around 7 ng/mL in the FDA trial), above the screening threshold. Benzophenone formation comes from one lab group's analysis of products and has been disputed in published letters; no study has measured health effects in users. FDA lists it as needing more data; the EU caps it at 10% (9% in propellant sprays) and requires benzophenone to be kept at trace level.

What it's used for, checked

UVB protection and avobenzone stabilisation

Holds up

Its main value is keeping avobenzone working through sun exposure.

Forms benzophenone in the product

Mixed

Shown in one lab study of 16 products (amount rose with ageing); disputed, and not linked to harm in users. Using sunscreen within its shelf life and not storing it hot limits degradation.

Harms reefs

Unproven

Some aquatic studies show effects at high concentrations; field-relevant risk is not established.

Works well with

  • avobenzone

Who should be careful

  • Photoallergy is the main risk, especially if you have ever reacted to ketoprofen gel (a topical anti-inflammatory): choose an octocrylene-free product.
  • Children occasionally develop contact allergy from octocrylene sunscreens; if a rash appears where sunscreen was applied, see a clinician for patch testing.
  • Discard sunscreen past its expiry date or after it has been stored hot.

The studies

Every citation is checked against its PubMed record.

  1. Benzophenone Accumulates over Time from the Degradation of Octocrylene in Commercial Sunscreen Products.
    Downs CA, DiNardo JC, Stien D, Rodrigues AMS, Lebaron P · Chem Res Toxicol · 2021 · Laboratory analysis

    Sixteen octocrylene-containing sunscreens from the EU and US contained benzophenone at an average 39 mg/kg, rising to 75 mg/kg after an accelerated-ageing protocol; a product without octocrylene had none. Shows a degradation pathway in the bottle, not a measured harm to users; the paper drew published critical letters.

  2. Contact and photocontact allergy to octocrylene: a review.
    de Groot AC, Roberts DW · Contact Dermatitis · 2014 · Review

    Photocontact allergy to octocrylene has been reported increasingly since 2003, mainly in adults previously sensitised to the anti-inflammatory gel ketoprofen; plain contact allergy is rarer and seen mostly in children using octocrylene sunscreens.

  3. Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial.
    Matta MK, Florian J, Zusterzeel R, et al. · JAMA · 2020 · RCT (pharmacokinetic)

    48 healthy adults applied one of four sunscreens to 75% of the body, up to 4 times a day for 4 days. Avobenzone, oxybenzone, octocrylene, homosalate, octisalate and octinoxate all exceeded the FDA's 0.5 ng/mL screening threshold after a single application; oxybenzone reached about 258 ng/mL from lotion. The authors state this does not mean people should stop using sunscreen.