the real reason why you need to apply sunscreen 20 minutes before sun exposure

Have you ever wondered why you’re always told to apply sunscreen 15/20 minutes BEFORE sun exposure?

If you’re anything like me, you’ve often put it on 5 minutes before leaving the house. Aham… What can I say? Girl’s busy…

But does it matter – as long as you put it on in the first place, I mean?

Yep. There’s a scientific reason why you need to put it on 20 minutes earlier… and it has NOTHING to do with sunscreen activation.

Sunscreen Activation Is A Myth

Mea culpa.

Rumour’s going round that mineral sunscreen (i.e., those with zinc oxide and titanium dioxide) work straight away while chemical sunscreens need to be activated by binding them to the skin. This chemical reaction supposedly takes 20 minutes.

For the longest time, I believed this rumour. Like you, I was honestly convinced this was the real reason why you need to apply sunscreen 20 minutes before going outside. Wasn’t that what even science-bent beauty blogs were telling us?!

Thanks to the research work of Reddit cosmetic chemist Stephen Ko, we now know that’s BS. Both mineral and chemical sunscreens work straight away.

Heck, they’d work even in the bottle – if the bottle were transparent and UV rays could get through.

So that’s definitely NOT the reason why you need to apply your sunscreen 20 minutes before sun exposure. But what the heck is it then?

Related: What’s The Difference Between Physical And Chemical Sunscreen?

How effective is your sunscreen? Sign up to the newsletter below to receive the “Sunscreen Audit” Worksheet and find out if your sunscreen is really up to the job:

The Real Reason Why You Need To Apply Sunscreen 20 Minutes Before Sun Exposure

Think of sunscreen like self-tanner. If you don’t distribute it evenly, you’ll tan in spots. Some areas will be darker and others lighter.

Sunscreen works the same way. If you don’t apply it evenly, you won’t get the same protection everywhere.

It’s not just a matter of applying the same amount on every area. You need to give it time to dry and form a uniform film on your skin.

Here’s how it works: when you apply sunscreen on your face, some of the product evaporates, leaving a thin layer of UV filters on your face. This film forming process takes about 15-20 minutes.

If you don’t disturb it…

The “sunscreen must bind to the skin” myth isn’t totally false. It’s true this binding process DOESN’T activate your sunscreen. BUT it does help it adhere better to your face.

Have you ever touched self-tanner/paint/nail polish while they were still fresh? If you did, you know you’re removing some of the pigment and you need to touch it up again.

Sunscreen works like that. If you rub your face, sweat, and even apply makeup before the sunscreen has had time to dry down and form the protective film on your skin, you’ll likely be removing some of it, compromising the protection you’re getting.

So don’t touch your face (and any other area where you’ve applied your sunscreen, of course) for at least 15 minutes, ok?

By the way, if you’re curious to know what my fave sunscreens are, check out these guides below:

The Bottom Line

If you want to maximise the protection of your sunscreen, always put it on 20 minutes before sun exposure. Skip this rule and you won’t get even protection everywhere!