For your skin
A common chemical UVB filter you will see near the top of many US sunscreen labels. On its own it is weak, so it is always combined with other filters and often does double duty dissolving avobenzone. It is effective for daily UVB defence; the open question is systemic absorption, which is why the FDA has asked for more safety data rather than declaring it fully proven-safe.
Want the science? Keep reading ↓Mechanism of action
Salicylate UVB filter that absorbs radiation in the 295-315 nm range. It is a relatively weak absorber, so US formulations use it at high concentrations (up to 15%) and pair it with other filters; it also helps solubilise poorly-soluble filters such as avobenzone. It provides no UVA coverage. Homosalate showed meaningful systemic absorption exceeding the FDA 0.5 ng/mL toxicology threshold in a maximal-use pharmacokinetic trial (Matta 2020), which is why the FDA has requested further safety data before granting it GRASE status.
Why we tier this moderate
2 cited papers across 1 country. The mechanism is well-described and there's at least one controlled trial in the literature, but we tier this Moderate rather than Strong to stay honest about how many specific papers we cite directly.
Cited research
Matta MK et al., Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial, JAMA 2020;323(3):256-267 — homosalate showed systemic plasma absorption above the FDA 0.5 ng/mL toxicology threshold
FDA Proposed Rule, Sunscreen Drug Products for Over-the-Counter Human Use, 84 FR 6204 (26 February 2019) — FDA requested additional safety data (GRASE status pending) for homosalate and the other organic UV filters
Sources: PubMed · KCI · J-Stage · CNKI · Wanfang · SFD · MFDS · Cochrane · SCCS · CIR. Every entry points to a specific document. See methodology for what each outcome label means.