Butyl Methoxydibenzoylmethane

When you see this mouthful on an ingredient list, you’re usually looking at one of the most important UVA filters in modern sunscreen. That matters because UVA rays are the sneaky ones: they go deeper into your skin, contribute to premature ageing, and are present pretty much all year round, even when it’s cloudy and you’re definitely not in a beach-movie montage. In practical terms, this ingredient has been the workhorse for broad-spectrum formulas because it covers the UVA range from about 310 to 400 nm, with especially good performance around 360 nm.

The catch is that it has a bit of a diva problem. By itself, it is not photostable, which means sunlight gradually breaks it down and weakens its UV protection. In one often-cited study, it lost about 36% of its UV-absorption capacity after just one hour of sunlight. That’s why formulators rarely use it alone. They usually pair it with stabilizers such as octocrylene or newer UV filters, and sometimes they use encapsulation tricks to help it hold up better. In real life, this is also one reason why sunscreen needs reapplying: your filter system is doing a job, and sunlight is very much trying to fire it.

It’s also worth knowing that this filter has played a big role in the sunscreen world because it has long been one of the few widely available chemical filters that gives solid UVA protection. That said, it is not the whole story of sun protection, and the final effectiveness depends on the full formula, not just one ingredient. Regulations also vary: the maximum allowed concentration is 5% in the EU and 3% in the US. Overall, its safety profile is considered pretty good, and it’s generally regarded as non-irritating and not estrogenic in the way some older concerns about sunscreens have been discussed.

One last geeky detail: you may know it by its much friendlier nickname, avobenzone. Same ingredient, just a name that sounds less like a failed chemistry quiz and more like something you’d actually want in your sunscreen.

The famous Avobenzone. It is a special snowflake as it is the only globally available chemical sunscreen agent that provides proper UVA protection (in the US, new generation sunscreen agents are not approved because of impossible FDA regulations). It is the global gold standard of UVA protection and is the most used UVA sunscreen in the world. 

It gives very good protection across the whole UVA range (310-400 nm that is both UVA1 and UVA2) with a peak protection at 360 nm. The problem with it, though, is that it is not photostable and degrades in the sunlight. Wikipedia says that avobenzone loses 36% of its UV-absorption capacity after just one hour of sunlight (yep, this is one of the reasons why sunscreens have to be reapplied after a few hours).

The cosmetic's industry is trying to solve the problem by combining avobenzone with other UV filters that enhance its stability (like octocrylene, Tinosorb S or Ensulizole) or by encapsulating it and while both solutions help, neither is perfect. Interestingly, the combination of avobenzone with mineral sunscreens (that is titanium dioxide and zinc oxide) is not a good idea. In the US, it is flat out prohibited as avobenzone becomes unstable when combined with mineral sunscreens.

As for safety, avobenzone has a pretty good safety profile. It counts as non-irritating, and unlike some other chemical sunscreens, it shows no estrogenic effect. The maximum concentration of avobenzone permitted is 5% in the EU and 3% in the US.