This is the real reason why you should never use last year's sunscreen

It's a reflex that many people have: as soon as the first rays of sunshine appear, you pull out your tube of sun cream thinking you're doing the right thing. We coat ourselves with the product, believing that we are protecting ourselves against UV rays. But after spending a year in the back of your closet, your sun creammay no longer have any protection.

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Sun cream has an expiration date

This was explained to Numerama by Christine Lafforgue, a biologist at the Paris-Sud University:

You can’t keep sun cream from one year to the next: the molecules will be less effective at protecting the skin.

Without you knowing it, a chemical process occurs in your tube of sunscreen. And time doesn't help it keep its properties.

The ‘classic’ composition of sun cream is as follows: an emulsifying base (like cream), preservatives, stabilisers, anti-free radicals (such as vitamin E or C) and ultraviolet filters. The latter has a crucial role since they serve to prevent ultraviolet B rays that cause sunburn, and ultraviolet A rays that cause premature skin ageing.

Moreover, it has been revealed that your sun cream usually last for 3 years. But 3 years is the lifespan of an unopened tube. Once it is opened, the cream loses its efficiency rather quickly. Reportedly in a matter of a few months. If you are unsure about how long your open tube of suncream can last, the expiration date is usually written on your tube.

This is your sign to throw away last year's cream

Inside your tube, the sun cream thus forms a chemical cocktail that protects you thanks to what are called conjugated double bonds. And as in a good mayonnaise, the recipe for success lies in the right dosage of the different ingredients. While it works in a brand new tube, no sun cream is designed to last and be reused from one year to the next.

And for good reason, sunscreens generally suffer from prolonged exposure to the sunandheat, by spending several hours in your beach bag. Despite the preservatives, even the most resistant of creams lose their effectiveness. Laurence Coiffard warns:

If your tube is not empty at the end of the summer, it means you haven't protected yourself enough. Sun cream is a product intended to be used up. As soon as you get back from your holiday, it should go right in the bin.

Moreover, using old sun scream could have disastrous consequences ranging from a simple sunburn to disruption of your endocrine system. Indeed, sun cream use ingredients that, over time and with over exposure to heat and sun, can become cancerous.

So don't be cheap and go to the pharmacy, right now!

This article has been translated from GentsideFR

Read more: Here's what to do if you get sunburnt this summer

Sources:

CNRS: Un filtre présent dans de nombreuses crèmes solaires se transforme en un composé cancérigène

Mayo Clinic: Is sunscreen from last year still good? When does sunscreen expire?