Homosalate
You may not have heard of homosalate before. Still, if you're using sunscreen every morning (insert obligatory reminder that daily SPF is a non-negotiable), there's a good chance that you're using the ingredient daily without even knowing it. Sunscreens fall into two camps: physical formulas (which rely on minerals such as zinc oxide and titanium dioxide to sit on top of the skin and deflect rays) and chemical formulas (which rely on chemical ingredients that penetrate the skin and absorb UV rays before they can cause irritate.
TYPE OF INGREDIENT: Chemical sunscreen
MAIN BENEFITS: Absorbs UV rays, specifically UVB rays, to ward off damage to the skin cells' DNA known to cause cancer, says Fincher.
WHO SHOULD USE IT: Everyone should use sunscreen daily; however, those with sensitive skin may prefer to opt for mineral-based sunscreens.
HOW OFTEN CAN YOU USE IT: If you're using a sunscreen with homosalate, it can, and should, be used daily and even reapplied every two hours for maximum protection.
WORKS WELL WITH: It's always paired with other chemical sunscreens such as avobenzone, octinoxate, and octisalate to ensure complete, broad-spectrum UV coverage.
DON'T USE WITH: There aren't any specific ingredients known to interact poorly with homosalate, but it (and other chemical sunscreens) can cause skin irritation for some.
What Is Homosalate?
"Homosalate is an organic compound belonging to a class of chemicals known as salicylates," explains Petrillo. It's a chemical sunscreen that shields the skin from sun exposure by absorbing UV light and converting it to heat so that it can't cause DNA damage to the skin cells, he adds. There are plenty of other chemical sunscreen ingredients, but homosalate is incredibly common. In fact, it's found in almost half of commercially-available sunscreens, notes Fincher.
According to Petrillo, there isn't a huge difference between the various chemical sunscreen ingredients, all of which work the same way. The differences lay in terms of which specific UV rays they can absorb and protect against
- UVB-blocker: Homosalate, in particular, is a UVB-blocker, protecting against the UV damage that is known to cause skin cancer, says Fincher. To that point, "since it has very limited efficacy against UVA rays, it needs to be combined with other agents to ensure complete protection," adds Idriss. (She also notes that homosalate isn't particularly photostable and needs to be combined with other ingredients to keep it stable as well.)
- Broad-spectrum sunscreen ingredient: It's this combination of chemical sunscreen ingredients, some of which work against UVA rays and some of which work against UVB rays, that will offer a larger range of protection so that a sunscreen can be called "broad-spectrum," notes Fincher.
Skin irritations and/or allergic reactions to homosalate are the biggest side effect, says Fincher (the same goes for pretty much any chemical sunscreen ingredient). As a general rule of thumb, that's why mineral-based formulas are usually recommended for sensitive skin.
Otherwise, the big elephant in the room is whether or not homosalate and its counterparts are safe. You've likely seen buzzy headlines that link sunscreen usage to cancer, but according to the experts we spoke with, it's not quite that simple (or scary). The FDA is currently investigating homosalate and other active chemical sunscreen ingredients. Studies have shown that most of these chemicals are absorbed through the skin and can be detected in the blood, explains Fincher. However, he underscores that there aren't any studies in humans that have shown any adverse effects from this absorption. There's some concern about homosalate being an endocrine disruptor and affecting hormone production. However, these studies have all been done in vitro, and there's no definitive in vivo data, points out Idriss, who says further research is still needed.
How to Use It
Unsure if you should use homosalate, given all of that information? "We know for certain that these chemical ingredients are effective in preventing DNA damage and skin cancer, and there are no known adverse effects on humans," says Fincher. Sunscreens have been protecting us for a long time, and for now, the more immediate threat is UV rays and their ability to cause skin cancer, rather than the issues surrounding the ingredients, adds Petrillo.
The bottom line: Any risk of using a chemical sunscreen is far less than that of using no sunscreen at all. But, if you are concerned, go ahead and pass on the homosalate and other chemical 'screens and opt for mineral formulas instead. Either way, make sure you're using a broad-spectrum formula with at least an SPF 30 and reapplying every two hours.