Sunscreen Math: Can You Add Up SPF?

by Gio
Can you layer sunscreen and add up spf

If you use a moisturiser with SPF 20, a sunscreen with SPF 30, and a foundation with SPF 15, what SPF do you get?

30 + 20 + 15 = 30.

Confused much? SPF math isn’t like regular math. Here’s why:

Does Layering Sunscreens Increase Sun Protection?

Layering sunscreens will NOT give you added SPF protection.

In the words of Mona Gohara, a dermatologist and an associate clinical professor of dermatology at Yale University, “SPF isn’t an equation. Your sun protection is only as strong as your highest SPF.”

In the example above, the highest SPF is that of your sunscreen, SPF 30. That’s what you’re getting. No matter what else you apply, that number won’t go up.

Why? Sunscreen works by limiting the number of UV rays that hit your skin. SPF 30 for example, makes 97% of UV ray harmless. But the remaining 3% still get through.

Let’s see what this means in practical terms using the example below.

Your foundation has SPF 15. That allows 7% of UV rays to reach (and harm) the skin. But you’ve learned a moisturiser with SPF 20 underneath. That allows only 5% of UV rays to reach the skin. 2% of the rays that made it through your foundation are now neutralised by your moisturiser.

But you have a third layer on. Your sunscreen with SPF 30 only lets 3% rays through, neutralising a further 2% that made it past your foundation and moisturiser with SPF.

The higher the SPF, the fewer % of UV rays reach the skin. Unfortunately, no sunscreen blocks 100% of them. Even SPF 100 still lets 1% through.

If applied correctly, that is…

Related: Take A Number: What Level Of SPF Is Right For You?

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

Is Layering Sunscreens Useless?

Layering products with SPF will not add up SPF, but it may increase your overall coverage.

Let’s say you’re in a rush and applying sunscreen quickly. It’s easy to miss a spot or two. Those spots have no protection and are fair game for UV rays.

But if you slather on a second SPF product, you have more chances of covering every little nook and cranny.

One study found that “the combined effect of two sunscreen applications gave on average 2.3 times better protection from UVR than a single sunscreen application.”

I personally don’t do this because I am very diligent with sunscreen application, but if you think you need it, go ahead.

WARNING! If you don’t apply the recommended amount (1/4 of a teaspoon for the face alone), you may get better coverage, but you won’t get the SPF stated on the label.

Related: Are You Applying Sunscreen The Right Way?

The Problem With Layering Sunscreen

If you decide to layer sunscreens to get that extra bit of sun protection, be careful.

Not all UV filters work well together. Some can deactivate each other and compromise the level of protection you’re getting.

In particular, beware of mixing Avobenzone with Octinoxate, Zinc Oxide, and Titanium Dioxide.

If you’ve just checked the label of your fave sunscreen and noticed it contains a few of these (for example, Avobenzone and Octinoxate), don’t throw it in the bin yet!

Cosmetic chemists know all kinds of tricks to make UV filters get along. For example, by coating them so they give you the best protection without getting too close to each other.

It’s when you use separate products that were never meant to be mixed together that you may get in trouble.

How To Layer Sunscreens The Right Way

I’m not a fan of using different sunscreens. It may help, but unless you know more about the formulations and how UV filters interact with one another, you may reduce – rather than increase – sun protection. Ouch!

But if you still want to do it, here’s how to do it right:

  1. Reapply the same sunscreen twice: You still get the same level of SPF, cover every nook and cranny, and run no risk of deactivating UV filters.
  2. Use two sunscreens with the same (or similar) UV filters: You’ll still get the highest SPF level of the two, better coverage, and a much lower risk of anything deactivating UV filters.

The Bottom Line

SPF works by limiting the amount of UV rays that actually reach your skin. Layering sunscreens and products with SPF won’t give you a higher SPF. But it may give you better coverage.

Do you stick to sunscreen only or do you layer several products with SPF every day? Let me know in the comments below.



Socialite Dreams June 19, 2012 - 7:44 pm

most foundations and face creams have spf in them, so i end up mixing products with spf. works for me!

beautifulwithbrains June 19, 2012 - 8:58 pm

Socialite Dreams, that’s true. I guess because so many products contain SPF these days, we all tend to layer them, even if don’t do it on purpose. πŸ™‚

Janessa June 20, 2012 - 3:08 am

I just stick to sunscreen though I have been using SPF moisturizer because I can get that into my hairline without it caking up and then I’ll blend some actual sunscreen into there and it works better (smoother application). Sometimes I use sunscreen for my brows (they’re a light black and taupe colors work best for filling them in) and sunblock for my face so that my brows don’t turn salt-and-pepper-grey on the days I don’t want to fill in my brows.
I have a question! I am in higher altitude and will be hiking up mountains to even higher elevations. I’m currently at 6035 ft or 1839meters above sea level lol… and it’s so dry here and it’s quite harsh on my already dry skin not to mention the literally scorching sun on my pale skin. I’ve been applying sunblock and touching up through the hot, slightly sweaty days (sorry if that’s gross) and I’ve brought my UPF 50 hat and wear long pants but what can I do? I’m just looking for advice. I really don’t want to burn lol. I burn with sunscreen (not sunblock) on.
<3 you are the person I trust and look up to!

beautifulwithbrains June 20, 2012 - 5:25 pm

Janessa, if you’re already applying sunscreen regularly and wearing protective clothing, I don’t think there’s anything more you can do unfortunately. If you still burn with the sunscreen you’re using, maybe you can try another one. The only other thing I can think of is to stay in the shade, but I know that’s not always possible.

Janessa June 20, 2012 - 6:29 pm

Okay, thank you so so much! You are the best! :] And I read your replies to other comments sometimes. You put all your heart into answering them! πŸ˜€

beautifulwithbrains June 21, 2012 - 8:42 am

You’re welcome. And aww thanks! 😳 I do my best to answer them as best I can.

Paris B June 20, 2012 - 6:17 am

This is a good post to think about. Many people think that by layering they can increase SPF coverage when nothing is further from the truth. I read somewhere once that the tip to bear in mind is that the highest SPF product you apply is the one that counts. The rest don’t. So I go with a high SPF sunscreen and I don’t mind or bother if other products (makeup/skincare) contain no SPF because I’m already protected πŸ™‚

beautifulwithbrains June 20, 2012 - 4:55 pm

Paris, that’s so true. Like you, I always use sunscreen too, so I don’t really mind whether the other skincare products I use contain SPF or not. I think that, while layering products may slightly increase your coverage (ie less chance to miss a spot), if you’re careful with application that shouldn’t be a problem anyway.

xin June 20, 2012 - 8:28 am

i used to have the misconception of layering sunblock will have higher spf too! much later only i found out that i was wrong. i only use sunblock as my main spf, and top with powder sunblock for double protection

beautifulwithbrains June 20, 2012 - 4:51 pm

Xin, unfortunately most people think so and it’s a shame. Glad you’ve found out the truth and are using sunblock now instead than reliable solely on cosmetics.

Pink January 30, 2015 - 6:33 am

I also heard that we shouldn’t mix products with SPF as they may interfere with each other and therefore give us less protection. So many sources and so many different opinions, it’s really hard to get some conclusion πŸ™

Gio January 30, 2015 - 9:39 pm

Pink, that’s only partly true. Zinc oxide and titanium dioxide can degrade avobenzone, making it less effective. But that just means that you need to reapply the sunscreen more often. Or better yet, avoid using this combination. Hope this helps. πŸ™‚

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