He continues, “The ingredients in chemical sunscreen, such as oxybenzone, avobenzone, and homosalate are more prone to oxidation [in sunlight], making them less effective over time.”
On the other hand, “mineral agents, such as zinc oxide, titanium dioxide, and iron oxide, are inert and much slower to break down [under heat or direct sunlight]”—either on your skin or in the bottle, says Serena Mraz, MD, a board-certified dermatologist in California.
In either case, experts agree that improperly storing your favorite sunscreen can significantly reduce the shelf-life. Storing your sunscreen in a cool, dark place will help you maximize its best-by date. “Sunscreen, like any skin-care product, is best stored in cool or moderate room temperature conditions,” says Dr. Mraz. This means out of direct sunlight (and hot cars). “When out, put sunscreen bottles in the shade, wrap them in a towel, or place them in a cooler,” recommends Dr. Ibrahim.
You should not use expired sunscreen—here’s why
Using expired sunscreen comes with all the downfalls you’d expect: It might smell weird and the texture might be off. But using expired sunscreen can also be quite dangerous. “Expired sunscreen is problematic because it will potentially give the user a false sense of security about the degree of protection provided,” says Dr. Mraz. While you dutifully lather on your sun protection, the very ingredients that are intended to keep you safe from harmful rays might not be doing their job.
“In the US, there are 16 approved UV filters,” says King. (These are the ingredients that either block or absorb and stop sun rays from reaching your skin.) “These filters do degrade over time.” So the bottle you’re using might say SPF 30, but the effectiveness could be closer to SPF 15 if that bottle is expired. “You will not get the same protection,” King adds.
What exactly does that mean for your skin? Says Dr. Ibrahim, “Using expired sunscreen leads to sunburns and carcinogenic DNA damage in the skin,” which can lead to skin cancer. Every time you get a sunburn, the DNA in your skin cells is damaged—and that sun damage never goes away. “Other ingredients and certain oils can go bad over time, which can irritate the skin or cause breakouts,” adds Dr. Ibrahim.
King says sun exposure only accelerates any potential irritation caused by expired products. So, if not a harmful sunburn, you might get a rash or nasty breakout from using expired sunscreen in the sun—and that’s reason enough to pick up a fresh bottle.