Sunscreens are marvels of modern engineering: Not only do they reduce the amount of ultraviolet radiation that hits our skin, they’re formulated to keep a thin layer of protection all over the area they cover, while also being only a little bit sticky or greasy.
But that formulation is more fragile than we might realize. Small changes to the way we store and apply sunscreen can change its consistency, which in turn can change the protection we get from them. Here are three things that can potentially make your sunscreen less effective.
Keeping it in a hot car
Table of Contents
Full disclosure: I’m guilty of this one. It’s so easy to forget the sunscreen when you head to the pool or leave for a hike in the blazing heat, so I keep a bottle of sunscreen in my car—that way, I know it’ll be there when I get to my destination. Unfortunately, though, sunscreen can break down in the heat, especially the extreme heat of a parked car. The FDA recommends storing sunscreen away from heat and (ironically) keeping bottles out of the sun. Sun-baked sunscreen may lose its efficacy well before its three-year expiration date.
If you bring your sunscreen to the beach or if you need to leave it in your car for a day’s outing, you can protect it by sticking it in your cooler or wrapping it in towels for insulation. And that bottle of sunscreen that’s been in your car all summer? It should really be replaced with a fresh one that you store indoors.
Freezing your sunscreen
While freezing sunscreen in an ice cube tray probably feels good when you apply it, it’s also messing with the product’s formulation. One viral TikTok video featuring frozen sunscreen cubes has a top comment from the sunscreen brand it used, reading “Thanks for using NIVEA 🥰 We recommend to use in normal temperature.”
Chemist Michelle Wong explains that sunscreens are an emulsion, with water surrounding tiny bubbles of oil. When the water freezes, the oily and watery parts can separate, and it will no longer spread evenly. Even coverage is crucial for ensuring that a sunscreen is protecting you.
Try these mini sunscreens if you want something more convenient:
Putting it in a different container
Changing the container of your sunscreen doesn’t sound like it would make that big of a difference, but chemist Ava Perkins tested the idea and found that different containers can, indeed, affect the texture and thus the coverage of some sunscreens.
Perkins transferred samples of three sunscreens into glass, metal, plastic, and silicone containers, and found that in many cases the sunscreens separated, ruining that even-coverage texture that we know is so important. Often the separation was worse at higher temperatures. One type of container, a silicone tube, thickened all three samples, in some cases turning the sunscreen into a solid, chunky mess.
This informal experiment doesn’t mean that all containers will ruin your sunscreen, but it does put repackaging sunscreen into the same category as temperature manipulation: it could change the texture, thus changing the effectiveness. Based on that, Perkins says she “wouldn’t recommend” transferring your sunscreen into a cuter or more convenient container.