The main long-wave UVA filter in US sunscreens. Very effective but breaks down in sunlight unless the formula stabilises it.
Avobenzone absorbs UVA1, the long-wave UVA (peak around 357 nm) that penetrates deep into skin and drives photoageing. For decades it was the only organic (non-mineral) filter in US over-the-counter sunscreens with strong UVA1 coverage, so most American 'broad spectrum' chemical sunscreens rely on it.
Its weakness is that it degrades in sunlight. Formulators stabilise it with partners such as octocrylene or bemotrizinol. Paired with octinoxate it is notably unstable. In perfumes it is added in small amounts to protect the product from light, not your skin.
The only long-term randomised sunscreen trial (Nambour, Australia) used a sunscreen of 8% octinoxate + 2% avobenzone and found fewer squamous-cell cancers, less photoageing and, at 10-year follow-up, fewer melanomas. Avobenzone is absorbed into the blood above the FDA's screening threshold; that threshold triggers further testing and is not a toxicity limit. FDA still lists it as needing more safety data.
1,621 adults in Nambour, Australia, were randomised to daily or discretionary use of an SPF 15+ sunscreen for 4.5 years. Daily use cut the number of squamous-cell carcinomas by about 39% (rate ratio 0.61) but did not change basal-cell carcinoma, and caused no harm. The trial sunscreen combined octinoxate 8% and avobenzone 2%.
Ten years after the Nambour trial ended, the daily-sunscreen group had 11 new melanomas against 22 in the discretionary group (HR 0.50, borderline significance); invasive melanomas fell from 11 to 3. Small numbers, but the only randomised evidence on sunscreen and melanoma.
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.
Oxybenzone, homosalate, octinoxate and two other filters made breast-cancer cells proliferate in a dish; in immature rats, octinoxate and oxybenzone raised uterine weight only at very high oral doses (around 935 and 1,525 mg/kg/day). Avobenzone was inactive. Hazard screening, not evidence of effects at human exposure.