How does sunscreen really work?

7 FAQs about SPF, and why sunscreen should be your BFF.

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Curology Team
Jun 16, 2020 · 5 min read

Woman with spf sticky note on her face
We’re here to share what we know — but don’t take it as medical advice. Talk to your medical provider if you have questions.
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No matter your age or skin type, protecting your skin against the sun every day is the most important step you can take for the health of your skin. ⁣The science of sunscreen gives some pretty compelling evidence that sunscreen deserves the hype.

When you incorporate the right products with SPF into your skincare and makeup routine, it can bring out your best skin. If you're not already an avid sunscreen-wearer, this is a great place to get familiar with SPF and pick the right product for you.

How should you apply sunscreen?

First things first, if you’re wondering how to apply sunscreen on the face, it can depend on the specific product you use.

  • Lotions: Layer up! Sounds simple, but this advice can vary depending on the specific product you’re using, whether it has physical or chemical ingredients, and whether or not you’re wearing makeup — more on this in a sec!

  • Sprays: Spray your sunscreen into your hands, then massage onto your face. It’s typically best to use spray sunscreen in a well-ventilated area (or outdoors).

  • Sticks: Draw the stick across your face until your skin is covered in an even layer. Then, rub it into the skin. If the product seems hard to blend, try applying it on damp (not wet) skin.

  • Drops: Dispense drops directly on your face and blend with your fingers. Pro tip: don’t dilute with a moisturizer or foundation, which may diminish the sunscreen’s ability to protect your skin.

What does SPF mean?

SPF (Sun Protection Factor) is a number that measures a sunscreen’s ability to prevent UVB rays from damaging the skin. The number is based on testing that measures protection against sunburn or redness on sunscreen-protected skin compared to unprotected skin. Sunscreens labeled “Broad-Spectrum SPF” are best because they protect against both UVA and UVB rays.

How much SPF do you really need?

In terms of how much SPF you need, we recommend choosing a sunscreen with broad spectrum coverage and an SPF of 30 or higher. For extended outdoor activity, choose a water-resistant, broad spectrum (UVA/UVB) sunscreen with an SPF of 30 or higher.

Which is better: chemical or physical sunscreen?

There are two different kinds of sunscreen ingredients: chemical and physical. Both work just fine when it comes to protecting against UV rays. However, people with sensitive skin tend to prefer physical sunscreen. If your biggest concern is avoiding a white cast, then chemical sunscreen might be the way to go.

Chemical sunscreen

  • Contains ingredients like oxybenzone, avobenzone, homosalate, and octinoxate

  • Absorbs UV light so that it can’t penetrate the skin

  • May irritate or cause an allergic reaction for some people

Physical sunscreen

  • Contains titanium dioxide and/or zinc oxide, which may help soothe irritation

  • Physically reflects or “bounces” sunlight away from the skin

  • Certain kinds of physical sunscreen may leave a white cast on the skin (unless rubbed in well, micronized, or tinted)

How To Incorporate Sunscreen Into Your Skincare Routine

How do you apply sunscreen with makeup?

In most cases, you can think of sunscreen (both chemical and physical) as the last step of your skincare routine and the first step of your makeup routine.

Pro tip: Apply sunscreen before your makeup primer.

On the hunt for the best under-makeup sunscreen? Look for a lightweight sunscreen that leaves no white cast with an SPF of at least 30. Chemical sunscreens are pretty good sunscreens for a face full of makeup because of their absorbency. This is because sunscreens that soak into the skin make a smoother, more even surface than sunscreens that sit on top of the skin. You totally can use physical sunscreens, though, if that’s what you prefer. But because these formulas tend to be thicker and less absorbent, it might be harder to apply makeup on top.

But when you’re applying sunscreen over makeup, (i.e. if you’re reapplying throughout the day) absorption is not what you want! Not only can it mess up your makeup, but it has to penetrate all the other products you’re wearing to reach your skin. So choose a physical sunscreen to layer over your products. Want more tips on how makeup and sunscreen can go hand-in-hand? Read how to apply sunscreen over makeup.

How can I avoid getting greasy?!

We feel you — some people would rather risk UV damage than intentionally grease up their face. We’re obviously in the pro-sunscreen camp, though. The good news is that you can have the best of both worlds: sun protection and matte skin.

  1. Cleanse. Wash your face with a gentle, hydrating cleanser to help control oil. If you’re prone to oily skin, try an oil-absorbing face wash like Everyman Jack Volcanic Clay Cleanser.

  2. Powder. A mattifying powder (like the BareMinerals Mineral Veil Finish Powder) will keep your sunscreen in place and absorb excess shine.

  3. Blot. Blotting sheets can soak up excess shine. We like NYX Professional Makeup Blotting Papers, but just about any brand should work!

You can also reach for sunscreens labeled non-greasy or oil-free. You’ll also want to make sure your sunscreen of choice doesn’t have pore-clogging or irritating ingredients.

How much sunscreen should you apply?

Most people don’t apply enough sunscreen! The American Academy of Dermatology says most people only apply 25–50% of the recommended amount. Chances are, you should consider doubling the amount you apply, though this recommendation will vary person-to-person.

  • Body: about 2 tablespoons (1 oz), or enough to fill a shot glass

  • Face: a dollop about the size of a large pea

Keep these numbers in mind if you rely solely on your makeup for sun protection. It might be easier to get the recommended amount from regular ol’ sunscreen than caking on an unnatural amount of foundation. When in doubt, apply the two finger sunscreen hack.

How long does sunscreen last after being applied?

You should reapply sunscreen for every two hours you spend in the sun — even if you’re using more than SPF 30. If you’re swimming, apply sunscreen even more often, since it can wash off in the water.

If you’re not going out much then you probably only need to apply sunscreen once a day. But staying inside isn’t always enough sun protection on its own! UVA rays can penetrate ordinary windows, so definitely don’t skip your daily dose of SPF. And there’s no harm in reapplying if you like to sprawl out in a sunny indoor spot.

Want more sunscreen recommendations from our team of skincare experts? Find a sun protection guide for every type of skin below:

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Your questions, answered.

If you want to take the guesswork out of skincare, sign up for a free trial of Curology. Just take our skin quiz and snap a few selfies to be paired with one of our in-house medical providers, licensed to practice in your state. They’ll prescribe you a custom cream with a mix of 3 ingredients for your unique skin. We’re all about simple, effective skincare — nothing extra.

• • •

We’re here to tell you what we know. That’s why our information is evidence-based and fact-checked by medical experts. Still, everyone’s skin is unique—the best way to get advice is to talk to your healthcare provider.

Empowering you with knowledge is our top priority. Our reviews of other brands’ products in this post are not paid endorsements—but they do meet our medically fact-checked standards for ingredients (at the time of publication).

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Curology Team

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