how much sunscreen do you need to use?

Did you know that most people use only half the amount of sunscreen needed to keep skin safe from UV harm?

Sunscreen application is SO confusing. Like, everyone tells you to apply sunscreen liberally but what the heck does that even mean? A thick layer, half a teaspoon? It seems like no one knows.

What you know is that sunscreen is messy. Greasy. It leaves a white cast on your skin and never fully absorbs. If you can get away with using less… Can you get away with using less?

Let’s find out:

How effective is your sunscreen? Sign up to the newsletter below to receive the โ€œSunscreen Auditโ€ Worksheet and find out if your sunscreen is really up to the job:

How Much Sunscreen Do You Really Need To Apply For Maximum Sun Protection?

Here’s the deal: when scientists test sunscreen to determine its SPF, they apply 2mg of it per cm2 of skin.

Translation: that’s hw much you need to apply to get the SPF stated on the bottle. But how much is that?! It’s not like you can squeeze 2mg out of the bottle, apply it to cm2 of skin and repeat the process all over again until your entire face is covered.

Fret not. Here’s how much 2mg per cm2 is in real life:

  • Face only: 1/4 of teaspoon
  • Face and neck: 1/2 of teaspoon
  • Arms: 1 teaspoon each
  • Entire body: a shot glass

WARNING! These are general guidelines. If you have a bigger than average face, you’ll need a bit more. If you have a smaller face, you’ll need a little less.

That’s a lot of sunscreen, isn’t it? I mean, if you’re at the beach, a couple of applications from head to toe and your bottle’s already gone!

Related: Are You Applying Sunscreen The Right Way?

How Much SPF Do You Get If You Apply Less?

Rumour had it, if you applied half the amount of sunscreen, you’d get the protection of only the square root of the SPF. So a SPF 70 turns into a SPF 8.4!

Scientists calculated it with the Beer-Lambert law, a physics law that says that protection decreases exponentially with less sunscreen. Michelle of Lab Muffin has a great post about this, if you’re interested in the science behind this law.

But, I’ll keep this simple for you. Scientists used this law to theoretically judge how much application affected SPF. Until one day, someone, somewhere, decided to put this law to the test.

You know what they found out? The latest research shows that, with less application, SPF decreases linearly, not exponentially.

In other words, applying half the recommended amount gives you half the SPF. So a SPF 50 becomes a SPF 25. That’s more like it, isn’t it?

But don’t go using this excuse to apply less sunscreen now. What’s the point of buying SPF 50 if you don’t get the full protection out of it?

Do you apply enough sunscreen? Let me know how much sunscreen you use in the comments below.