I was pretty proud of my vast Solar cream collection until I began to wonder if I had just a ton of expired sunscreen on my hands. (Not literally, but you know.) I'm not talking about moisturizer with SPF I wear every day. Naturally, I quickly go through there. No, I mean the multitude of sunscreen options with a higher SPF than I'd hid specifically for skiing and going to the beach, which I only do a few days a year, as well as physical sunscreens that I use sporadically. to protect new scars. Unfortunately, in reporting this story, I learned that only two seven sunscreens from my stock were really usable.

Just as you should not take expired medication, you should not use expired medication. Solar cream. "A sunscreen is an over-the-counter drug – a medicine – and it should be considered as such," says cosmetic chemist Konstantinos Lahanas, Ph.D., founder of the cosmetic science research company. The Lahanas group, LLC, tells SELF.

The strange thing is that some sunscreen bottles do not have an expiration date. Even if yours does, the date can become fundamentally illegible over time. So, why should you buy a new bottle of sunscreen if yours is expired, and how can you say she's too old if you're not sure? Here, the experts answer these questions and more.

Here's why sunscreen expiration dates and how they work

The chemicals in all types of sunscreens break down over long periods of time and eventually become less powerful. John G. Zampella, MD, an instructor in the Department of Dermatology Ronald O. Perelman of NYU Langone Health, told SELF. Dr. Zampella has an analogy sweet enough to make clear at this point.

"Think about those strawberries for a week in your fridge. After being in the fridge for so long, they start to break down, "he says. "At first you may recognize them as strawberries, but they end up with mold and do not even look like strawberries anymore."

It's a similar story with your sunscreen, he says: "Eventually, just like your strawberries, all these compounds break down and the sunscreen becomes useless."

This is where the expiry dates come in (on the bottles that have them, anyway). All drug manufacturers (including those who manufacture Solar cream) must perform stability tests before they can sell their products, the US Food and Drug Administration (FDA) explains. Based on these tests, they can submit a drug application with a proposed expiry date and instructions for use so that you do not accidentally lose your sunscreen before that date.

the FDA recommends that drug manufacturers follow standard guidelines for stability testing, such as those described by International Council for Harmonization. The guidelines are full of complex technical terms and scientific hurdles to overcome for manufacturers. In summary, these recommendations essentially require manufacturers to exhibit at least three batches of the product at multiple storage conditions over months or years. Then, the manufacturers are supposed to perform all kinds of tests – physical, chemical, microbiological, and so on. – to determine how long their drugs will remain safe and effective under different conditions over time. (These recommendations are flexible, but it's essential.)

So, behind this tiny expiration date on your sunscreen bottle is hiding a considerable scientific effort to make sure that the drug will be as effective as possible until then, but not after. That's why the FDA and American Academy of Dermatology (AAD) both recommend throwing away your sunscreen as soon as it reaches its expiration date.

OK, but what happens if you use an expired sunscreen?

Honestly, everyone guesses, and that's why you probably should not do it. "If you use sunscreen after the expiry date, it may still have some anti-UV power, but it will not be all the power indicated on the label," says Dr. Zampella. Even a sunscreen with a high SPF, like 75, can not protect you reliably once it's expired, he adds. You can not tell if his post-expiration SPF has dropped to 70 or, say, 5 unless you have a chemistry lab in your house that you can use to analyze the product. In this case, let yourself cool and can we come back?

"The sunscreen does not have a time bomb built into that will. [immediately] to make it useless once expired, says Lahanas. But since there is no way of knowing how much (if any) of his SPF has stuck past its expiration date, any expired sunscreen should be considered ineffective, says Lahanas.

What happens if your sunscreen does not have an expiration date?

Sunscreens that are not labeled with expiry dates have been stable for at least three years, the FDA said. So, any sunscreen with no expiration date indicated "should be considered as expired" three years after the purchase, the FDA said.

An interesting point here is that your sunscreen may have been put on the shelf for a while before you buy it. Thus, after three years, it will have been manufactured more than three years ago and its stability countdown has begun. But all sun creams with no expiry date have proved their effectiveness for at least three years, not exactly three years, so that its conservation time will not necessarily affect its effectiveness. Obviously, it depends on how long the sunscreen works and how long it lasts, but it's not enough to ask the FDA to change its recommendation to consider a sunscreen without a date. Expiration expires three years later. purchase.

Basically, if you find a sunscreen container in the bottom of your beach bag with no expiration date and you have no idea when you buy it, you can also launch it.

"As with any other medicine, if in doubt, discard it," says Lahanas.

It's the same if your sunscreen has not reached its expiration date or if you bought it three years ago, but its color or consistency has changed in a fun way. AAD added. This can be a sign that its use is no longer safe. Sometimes this can happen sooner than expected if you store your sunscreen so that it breaks down faster than usual.

By the From the FDA As directed, you should keep the sunscreen at room temperature to keep the chemicals stable for as long as possible. It's hard to say if you wear sunscreen in a place like the beach so you can reapply it conscientiously. (Good job, by the way.) In this case, the FDA recommend wrapping the sunscreen container in a towel or throwing it into your cooler if you have one. In the same vein, you should not store sunscreen in your car, where it could overheat.

If you buy a sunscreen that has no expiration date, the AAD recommend writing your date of purchase on the container. This will help you get a better idea when the time comes. (Even if your sunscreen has an expiration date, you may want to write it back in case the original disappears.)

Finally, if you do not like to buy a sunscreen with no expiration date because you do not know how long it could miss out on this three-year stability guarantee, you can stick to the sunscreens containing expiration dates or buy. new sunscreen a lot more often than once every three years, like once a year just before the summer when you need maximum protection from the sun.

So you do not need to buy a new sunscreen every year, but you should probably.

Dermatologists often say that you should really use enough sunscreen so you do not have time to spoil yourself. This is a common chorus: if it takes a long time to get through a bottle of sunscreen (as if you only have one bottle all summer), you will not use it probably not enough.

Certainly, this kind of thing depends a little on your habits, as if you prefer to spend every weekend in the company of blessed air conditioning instead of frolicking in some waves or spending a lot of time outdoors. All in all, however, it would certainly not be harmful to apply your sunscreen in the proper way diligently and often enough so that you never have to worry about its expiration.