Homosalate is an ingredient commonly used in sunscreen to block out UVB rays. It has an average mass of 262.344 Da and the molecular structure C16H22O3.
As an active ingredient in sunscreen, homosalate is approved by the United States Food and Drug Administration for use as a UVB blocker at a concentration of up to 15 percent. The FDA considers homosalate non-toxic and non-sensitizing. It is most often found in sunscreens offering a maximum of SPF 30 protection.
Homosalate is an effective sunscreen ingredient because it is able to block light in the wavelengths between 295-315 nm. However, this range is too narrow to include much UVA protection. Also, because of this narrow range, homosalate is not considered sufficient protection from the sun on its own, even for just UVB rays. Instead, it is most often used to augment other forms of UVB protection.
Chemically, homosalate is a salycilate, a derivative of salicylic acid. It is oil soluble and classified as a sun-locking agent because it absorbs UVB radiation. However, once exposed to sunlight, there is some chemical degradation of homosalate, which may or may not affect its ability to block UVB rays. There is not enough data to support a conclusion either way.