A weak UVB filter used mainly to top up SPF and help dissolve other filters. Low allergy risk; absorbed, like most organic filters.
Octisalate is a salicylate that absorbs UVB (peak around 307 nm). It is weak on its own, so it is almost always one of several filters, adding a little SPF and acting as a solvent that keeps crystalline filters such as avobenzone dissolved.
In perfumes it is added in small amounts to protect the scent and colour from light.
Its UVB absorption is well characterised, but its contribution to a product's protection is modest. The FDA trial found blood levels around 5 ng/mL, above the screening threshold. There is no human evidence of harm; FDA lists it as needing more safety data.
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.