Avobenzone

Ultraviolet light comes in two bands that matter. UVB burns, and it is what SPF measures. UVA penetrates deeper, contributes to ageing and to cancer risk, and SPF says nothing about it.

Avobenzone is the answer to the second half. Among organic filters approved in the United States it was, for a long time, the only widely available one covering UVA, which put an unusual amount of weight on a molecule with a specific weakness.

The problem is the job

Avobenzone is described in the literature as “intrinsically photolabile”. Light breaks it down. A review of the filter landscape puts the consequence directly: this “reduces photoprotective efficacy and requires the use of stabilizers”.

Read that again with a sunscreen in your hand. The ingredient protecting you from ultraviolet light is degraded by ultraviolet light, so the protection it gives at hour three is not the protection it gave at minute one, unless the formulator did something about it.

This is not a scandal and it is not hidden. It is a known property that formulation science has spent thirty years working around. But it is the reason the reapplication advice on the bottle is not a sales tactic, and it is the reason two products with the same stated SPF can behave differently over an afternoon.

What stabilises it

Octocrylene is the most common answer, and its main reason for being in a formula is often not its own filtering but keeping avobenzone intact. Other filters and additives do similar work.

None of this is stated. An ingredient list tells you both are present and gives no indication that one is there to protect the other, or how well it is doing so. Photostability testing exists and its results do not appear on the pack.

What that leaves you with: if a sunscreen contains avobenzone, look for what is with it. Avobenzone essentially alone in an otherwise mineral-free formula is the configuration where the question bites hardest.

The absorption numbers, in proportion

The FDA maximal use trial that made headlines about Oxybenzone also measured avobenzone. Maximum plasma concentrations were 4.0 and 3.4 nanograms per millilitre for two sprays, 4.3 for a lotion and 1.8 for a cream.

That is above the 0.5 nanogram per millilitre threshold at which FDA asks for further toxicology, so avobenzone is in the same category of unfinished business. It is also roughly fifty times lower than the oxybenzone figures from the same study, which is worth stating because coverage of that trial tended to collapse four ingredients into one number.

The investigators wrote, of all of it, that “these results do not indicate that individuals should refrain from the use of sunscreen”.

What is changing

In June 2026 FDA added bemotrizinol to the sunscreen monograph at concentrations up to 6 percent, the first new filter in a very long time. It covers UVA and UVB, and unlike avobenzone it retains its integrity after ultraviolet exposure, which is set out on Bemotrizinol.

That does not make avobenzone products bad. It means the specific constraint this page is about now has an alternative in the US that the rest of the world has had for two decades.

For anyone who would rather avoid the question entirely, Zinc oxide covers UVA without degrading, at the cost of a visible cast.