How Much Sunscreen Should You Use?

by Gio
how much sunscreen do you need to use?

Most people use only half the amount of sunscreen needed to keep skin safe from UV harm – are you one of them?

Don’t feel bad. Sunscreen application is hella 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 Much Sunscreen Do You Really Need To Apply For Maximum Sun Protection?

Here’s the deal: when they test sunscreen to determine its SPF, scientists 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

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!

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.

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32 comments

xin July 17, 2012 - 1:21 pm

i usually am very generous with sunscreen, because more is better than less in this case!

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beautifulwithbrains July 17, 2012 - 7:59 pm

Xin, I agree. It’s always ok to apply more when it comes to sunscreen, but very dangerous to apply less.

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La Bisbetica July 17, 2012 - 2:22 pm

I guess (and hope!) I’m applying enough sunscreen. I think that people would be more prone to use the right amount of sunscreen if this was less thick and fragrance-free. The one I’m using for the body (Bottega Verde Sol SPF 50) has a strong chocolate-like scent; most of the times that I use it, I hear somebody saying “What’s this smell?”. It’s so embarrassing!

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beautifulwithbrains July 17, 2012 - 8:02 pm

La Bisbetica, I agree. I wish scientists would create a sunscreen that offers adequate protection even if you apply only a small amount.. I don’t mind scents too much in cosmetics, as long as they’re not too strong. That’s really offputting.

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Ana July 17, 2012 - 7:48 pm

No.
I simply don’t have enough money to afford that amount of sunscreen.

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beautifulwithbrains July 17, 2012 - 8:03 pm

Ana, it’s a shame that you have to apply so much isn’t it? Applying less is dangerous but if you use the right amount, you often run out of it in no time. I try to wear protective clothes as much as possible, but that’s not always possible especially in the summer.

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H March 28, 2016 - 2:57 am

Dang! I didn’t know that applying 1/2 amount only gave you the spf rating of the labels spf rating! I though it was more like for example if you applied 1/3 the amount you should you’d get an spf of 1/3 on the label.

To anybody coping with the $$ of sunscreen I think that to save money you don’t have to put it under your cloths;only where you’re cloths aren’t touching (mostly applying to indoors, people 🙂 ). Then you’d definitely not have to use even near a shot glass’s worth! I guess it wouldn’t be a sin if you put less on your body than recommended amount indoors,too, there,if you’re inside because 0 UVB go through windows and only 50% of UVA gets inside,so fortunately windows protect some. (I’d still put recommended amount of face for max protection) 🙂

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H March 28, 2016 - 2:58 am

I meant square root’s worth of spf rating on label.

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Gio April 3, 2016 - 1:01 pm

H, it would be great if it worked that way, but we only get the square root, unfortunately. 🙁

I agree, sunscreen can be so expensive, so apply the recommended amount only where necessary. There’s no point using more.

H April 3, 2016 - 7:06 pm

Totally. That would save you $$$. 🙂 Um, about it working that way, I meant square root. Just a little mistake when I was typing. 🙁

H April 3, 2016 - 7:08 pm

I meant using half the amount of sunscreen gives you the square root of the spf rating.Sorry for cluttering the comments section.

Gio April 8, 2016 - 1:29 pm

No worries, H. 🙂

audrey April 10, 2017 - 8:24 am

I calculated that even if we just use it on our face and neck (2.5ml per day) and we use $30/30 ml great elegant physical suncsreen (for under makeup) we will run out in just 12 days. So in a year we will have to buy 30 bottles of sunscreen –> 30 x $ 30 = $900. And that’s only for our face and neck. I definitely use less just because I can’t afford to buy a new bottle of $30 sunscreen every 12 days. I ended up using it for almost a year! But I work mostly indoor so I don’t exactly expose myself to too much sun anyways, just exposed a bit at the car when going to work.

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Gio April 10, 2017 - 12:02 pm

Audrey, yep, that’s the problem with sunscreen. They should come only in huge bottles at cheap prices but the reality is different. If you’re serious about sun protection, you’ll have to spend a small fortune!

audrey April 11, 2017 - 6:41 am

Even by using less product than the recommendation I truly felt the benefits of using sunscreen. So amazing! I will definitely try to budget more money into sun protection since I’m almost in my mid 20s now. Don’t want premature aging creeping up on me later on.

Gio April 21, 2017 - 8:24 pm

Audrey, smart lady! Any money invested now is money saved later.

Makeup Morsels July 18, 2012 - 1:29 am

I definitely use enough sunscreen on my face, but I don’t know about the rest of my body. I definitely apply enough so that I have to spend some time working it in, but a shot glass? Probably not. I’ve always known about that rule, but urghhh I don’t want to rebuy sunscreen every two weeks! I agree with all that was said up there, it would be great if someone could develop a sunscreen that needs less product for the same amount of sun protection.

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beautifulwithbrains July 18, 2012 - 5:58 am

Makeup Morsels, a shot glass is a lot, isn’t it? If you abide by that rule, you’ll gonna finish the bottle in no time! But not applying enough is never a good idea either. I try to wear pants and long-sleeved tops whenever I can to save on the sunscreen, but that’s not something you can do when it’s really hot unfortunately.

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Nikki July 18, 2012 - 3:11 am

You’re doing it right as I attended a “sunscreen” workshop or talk and it’s basically teaspoons they use, I don’t even get to apply half as much, I’m just too scared of the icky feeling! But yeah, I NEED to follow directions or I’m just wasting products!

Thanks for this.

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beautifulwithbrains July 18, 2012 - 6:00 am

Nikki, you’re welcome. Yes, some sunscreens are so thick that feel really icky on the skin. Just experiment until you find out that doesn’t. Wearing the right amount of sunscreen is too important. 🙂

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Phylisteen July 30, 2015 - 4:51 am

I work for Kiehl’s and am in love with our Super Fluid SPF 50. It’s featherlight in a vitamin E base and absorbs to a weightless matte finish. I use exactly 1/4 teaspoon and it feels smooth and like I don’t have another layer on. Formulation really matters in how comfortable a product feels.

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Gio July 30, 2015 - 5:55 am

Phylisteen, I’m glad you’ve found something that works so well for you. Formulation is very important indeed, and this one sounds great.

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Fane Davis July 18, 2012 - 3:58 am

i was like “oh?is it?” when i read this one. I didn’t know there is right way and amount of applying sunscreen.I usually apply it just like the moisturizer,with a small amount to avoid the greasy and shining face.In hope that a bottle of sunscreen will last me longer time.Now that i know i did not applied enough.:(
Thanks for the info…i will (hopefully) apply right/enough amount this time around.

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beautifulwithbrains July 18, 2012 - 6:01 am

Fane Davis, you’re welcome. Unfortunately, that’s what most people think, and what I used to do when I first started using sunscreen. Sadly, applying so little will give you little protection and still leave skin exposed to sunburn and premature aging. 🙁

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Janessa July 18, 2012 - 11:27 pm

I’m pretty sure I do! I use a plentiful amount and I don’t skimp on it because it’s precious. I feel like it’s worth it :]. Both chemical and physical sunscreens need 1/4 tsp?
I am so tired! :[

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beautifulwithbrains July 19, 2012 - 9:29 am

Janessa, according to Dr Schultz, if you use a chemical-free sunscreen, you can apply a bit less. You can find the full explanation here: http://www.dermtv.com/how-apply-chem-free-sunscreen. However, it’s not easy to find a sunscreen with only physical sunscreen ingredients. Most are a combination of both chemical and physical ones so I say pile it on. It’s always best to apply more than less in this case.

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Janessa July 20, 2012 - 5:55 am

Wow, thanks so much, Gio! You are so amazing, I even asked my roomies for a synonym for the word haha.

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beautifulwithbrains July 20, 2012 - 6:11 am

lol, thanks hun. I’m all red now. 😳

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Thurisaz Sala'il July 19, 2012 - 3:31 am

How do people use that little on their skin? >D My skin practically absorbs all moisture the second it hits, so I can use nearly a shotglass of sunscreen on just my arms and they’ll be dry in seconds. x.x I keep a separate sunscreen for my face, and I don’t need much there, but the rest of my body? O.o So I tend to wear covering clothing as often as possible, and apply on any exposed skin.

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beautifulwithbrains July 20, 2012 - 6:10 am

Thurisaz, lucky you! My skin would be all greasy if I used a shotglass only on my arm! lol

I tend to wear covering clothes as much possible too so that I can wear less sunscreen. 🙂

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Elizabeth August 19, 2012 - 9:31 pm

When I apply my sunscreen it goes on white then it clears up after a few minutes. Do I need to rub in the sunscreen until all the whiteness goes away or should I just slather on sunscreen making like a smooth white layer and then let it dry clear?? I usually rub it in a few times but I’m afraid if I rub it in too much then I’ll affect the protection I need and if I don’t rub it in enough it won’t absorb properly…

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beautifulwithbrains August 20, 2012 - 7:36 pm

Elizabeth, does your sunscreen contain Zinc Oxide and/or Titanium Dioxide? These ingredients are white minerals so it’s normal for them to leave a white cast on the skin. As long as you slather the appropriate amount on all areas covered, the protection shouldn’t be affected.

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