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Sunscreens are feats of modern technology: They not only block ultraviolet rays from damaging our skin, but they’re also designed to form a protective barrier that stays on the skin, with just a slight amount of stickiness or greasiness.
However, this protective formula is more delicate than we may think. Minor changes in how we store and apply sunscreen can alter its texture, which can ultimately impact its effectiveness. Here are three factors that could make your sunscreen less reliable.
Leaving it in a hot car
Full confession: I’m definitely guilty of this one. It’s so easy to forget sunscreen when heading to the pool or embarking on a hike under the blazing sun, so I keep a bottle in my car. That way, I know it’ll be there when I reach my destination. However, sunscreen can degrade in the heat, particularly the extreme temperatures of a parked car. The FDA recommends storing sunscreen in a cool place and (ironically) keeping bottles out of direct sunlight. Sunscreen that’s been overheated may lose its effectiveness well before its three-year expiration date.
If you’re bringing sunscreen to the beach or leaving it in your car for a day out, consider placing it in a cooler or wrapping it in towels for insulation. And that bottle of sunscreen that’s been baking in your car all summer? It’s best to replace it with a new one stored indoors.
Freezing your sunscreen
While the idea of freezing sunscreen in an ice cube tray might feel refreshing when you apply it, it’s actually altering the product’s formulation. One viral TikTok video showcasing frozen sunscreen cubes has a top comment from the sunscreen brand it featured, which reads “Thanks for using NIVEA 🥰 We recommend using it at normal temperatures.”
Chemist Michelle Wong explains that sunscreens are emulsions, with water surrounding tiny oil bubbles. When the water freezes, the oily and watery components can separate, causing uneven application. Even coverage is essential to ensure sunscreen provides proper protection.
If you're looking for something more travel-friendly, consider trying these mini sunscreens:
DUNE’s Jetsetter Gelly Pack, which includes three small, rounded bottles with different formulations (two SPF 30 sunscreens and one aloe lotion)
Sonew Face and Body sunscreen travel packets, SPF 46+ (set of 20)
L’autre Peau SPF 30 sunscreen spray pens (set of 3)
Transferring sunscreen into a different container
While it might seem like a small change, switching the container of your sunscreen can actually have a significant effect. Chemist Ava Perkins tested this idea in her honors undergraduate research project and found that the type of container can indeed impact the texture and coverage of certain sunscreens.
Perkins moved samples of three different sunscreens into glass, metal, plastic, and silicone containers. She discovered that in many instances, the sunscreens separated, disrupting the smooth, even texture that's so essential. The separation was especially noticeable in higher temperatures. One container, a silicone tube, caused all three sunscreen samples to thicken, sometimes turning the sunscreen into a solid, lumpy substance.
This experiment doesn't imply that every container will damage your sunscreen, but it does categorize repackaging sunscreen alongside temperature manipulation: it has the potential to alter the texture, and in turn, its effectiveness. As a result, Perkins advises against transferring your sunscreen into a more attractive or convenient container.
Updated September 27, 2023 to clarify that Ava Perkins's experiment was part of a formal research project, not an 'informal' experiment as we previously stated.
