We’ve all heard that it’s important to apply sunscreen every day to help protect against photoaging, skin cancers, and other kinds of damage that happen as a result of the sun’s UV rays.¹ But for maximum protection, it’s also key to reapply throughout the day, since even the most effective sunscreen won’t carry you from the morning to the evening. 

The specifics of reapplying, however, can get a little confusing. How often should you reapply and what are the best ways to do so? And do you really need to consistently pile on more sunscreen if you’re spending the day indoors? Here, our dermatology experts will break down what you really need to know.

Why is reapplying sunscreen important?

As much as we wish it did, sunscreen doesn’t stay effective all day long. And the sun's rays don’t quit, with UV radiation at its highest from 10am to 3pm.² The primary reason a sunscreen wouldn’t provide adequate protection is if it isn’t applied sufficiently and reapplied often enough.³ How much sunscreen you use matters—reapplying is important to make sure you have a thick enough layer of it on your skin, which correlates directly with how much you’re protected from the sun. One study in particular showed that the subjects in question applied less than they should, so reapplying can be an important step in maintaining adequate coverage.⁴

A variety of factors can lead to your sunscreen wearing off over time, as they increase the likelihood of it being removed, including the following:⁵

• Sweating

• Bathing

• Swimming

• Toweling off

It’s also likely that your sunscreen will begin to wear off at the beach because of exfoliation from the sand. If you’re wearing clothing that causes friction against your skin, that can also have an impact.⁶

Plus, there is no such thing as a completely waterproof or sweat-proof sunscreen, and the U.S. Food and Drug Administration (FDA) doesn’t allow companies to use these terms on their product labels.⁷ It’s almost impossible to prevent your sunscreen from rubbing off on an everyday basis—which is why reapplying is so important!

What does SPF mean?

SPF stands for “Sun Protection Factor.” It’s a measurement that can help determine the amount of protection offered by a sunscreen. SPF is a ratio of the smallest amount of UVB radiation necessary to cause redness on skin with sunscreen, to the amount of UVB radiation necessary to cause redness on skin without sunscreen.⁸

If that sounds confusing, think about it like this: Sunscreen with SPF 50 should protect you from direct sunlight until you experience 50 times more UVB radiation than what will cause you to burn without sunscreen.⁹  

According to the FDA, only products with an SPF of 15 or higher can claim to help reduce the risk of skin cancer and early skin aging.¹⁰ To protect your skin from sun damage caused by both UVA and UVB rays, we recommend choosing a broad-spectrum sunscreen with an SPF of 30 or higher.

How often should you reapply sunscreen?

According to the FDA’s requirements, sunscreen companies have to state on their labels whether their product is water-resistant or not.¹¹ Products that aren’t labeled as water-resistant should be reapplied at least every two hours. Those that are labeled as water-resistant should be reapplied after 40 or 80 minutes of swimming or sweating, at least every two hours, or immediately after towel drying.¹²

More tips for reapplying sunscreen

In order for sunscreen to work to its full effectiveness, it needs to be used properly—even when you’re reapplying! Here are some guidelines to keep you on track.

• Make sure you still reapply in the fall, in the winter, and on cloudy days, since you can still be exposed to UV radiation during these times.¹³ In general, practice applying before every time you go outdoors.

• If possible, reapply 15 minutes before sun exposure so your skin has time to soak up the product.¹⁴

• Consider reapplying 15 to 30 minutes after you go in the sun for maximum protection. One study found that reapplying sooner than recommended on sunscreen labels helped to reduce exposure to the sun’s rays. Specifically, the study showed that reapplying 20 minutes after going into the sun resulted in 60% to 85% less UV exposure than what would have been experienced if sunscreen was reapplied at the two hour mark.¹⁵

• Since you’re going to all the trouble to reapply, make sure to use enough sunscreen every time! The American Academy of Dermatology Association recommends using at least one ounce of product for your whole body each time you apply.¹⁶

• Try to make sure your sunscreen hasn’t expired before reapplying.

And, don’t forget your lips! Use our broad-spectrum Lip Balm with SPF 30 for year-round UV protection, and make sure to reapply at least every two hours.

How often should I reapply sunscreen while indoors?

Even if you’re spending all day indoors, don’t skip your sunscreen. While windows can block UVB rays, they typically allow UVA rays through—including the windows in your car! Even small amounts of UVA rays can cause significant changes to the skin.¹⁷

However, the risk of skin damage may be much less when you spend the whole day inside. One study found that indoor workers may not need to reapply sunscreen as frequently, but even so, make sure to apply at least once in the morning.¹⁸ You don’t need to worry about your computer monitors and lamps emitting UV rays, since research shows that they don’t.¹⁹ However, you may want to consider applying a sunscreen that contains titanium dioxide, iron oxides, or zinc oxide to protect your skin from the harmful effects of blue light.²⁰

How can I reapply sunscreen if I’m wearing makeup?

It’s still possible to reapply sunscreen if you’re wearing makeup—you may just have to take a few extra precautions! Here are some tips to get you started:

• Try using makeup products with skincare benefits. In this case, a foundation, BB cream, or CC cream with SPF. Just make sure the SPF is 30 or above and the sunscreen is broad-spectrum to protect your skin from sun damage.

• Try a powdered sunscreen that is made to go on top of your makeup.

• Use a face spray (such as a setting spray) with sunscreen over your makeup. 

• Use a sponge to press sunscreen over your makeup so you don’t mess it up.

• Make sure to start the day with a base layer of sunscreen under your makeup, even though it won’t last you all day.

You may also want to reapply more often than every two hours, especially when swimming or sweating! Sunscreen applied over makeup may slide off more quickly than your base layer, and it can be easier to miss spots.

Curology can help protect your skin

We know it’s important to reapply sunscreen at least every two hours throughout the day if you’re spending time outdoors, and more frequently if you’re swimming or sweating. But first, make sure you’re using an effective sunscreen!* To get advice on what products may work best for your skin—and to get your questions about sunscreen answered—reach out to a licensed dermatology provider at Curology.

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P.S. We did the homework so you don’t have to:

1. Sander, M., et al. The efficacy and safety of sunscreen use for the prevention of skin cancer. CMAJ. (2020, December 14).

2. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. (January 2013).

3. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid.

4. Wickenheiser, M., et al. Sun Protection Preferences and Behaviors among Young Adult Males during Maximum Ultraviolet Radiation Exposure Activities. Int J Environ Res Public Health. (August 2013).

5. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid.

6. Sander, M., et al. The efficacy and safety of sunscreen use for the prevention of skin cancer. CMAJ. Ibid.

7. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid.

8. Gabros, S., et al. Sunscreens and Photoprotection. StatPearls. (2023, March 7). 

9. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid.

10. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid.

11. Latha, M.S., et al. Sunscreening Agents. J Clin Aesthet Dermatol. Ibid

12. U.S. Food & Drug Administration. Over-the-counter sunscreen drug products; required labeling based on effectiveness testing. Code of Federal Regulations Title 21. (2023, June 7).

13. American Academy of Dermatology Association. How to apply sunscreen. (n.d.). 

14. American Academy of Dermatology Association. How to apply sunscreen. Ibid.

15. Diffey, B.L. When should sunscreen be reapplied? J Am Acad Dermatol. (December 2001).

16. American Academy of Dermatology Association. Sunscreen FAQs. (2023, July 19).

17. Wilson, B.D., et al. Comprehensive Review of Ultraviolet Radiation and the Current Status on Sunscreens. J Clin Aesthet Dermatol. (September 2012). 

18. Rungananchai, C., et al. Sunscreen application to the face persists beyond 2 hours in indoor workers: an open-label trial. J Dermatolog Treat. (August 2019).

19. Duarte, I.A.G., et al. Ultraviolet radiation emitted by lamps, TVs, tablets and computers: are there risks for the population? An Bras Dermatol. (July-August 2015).

20. Suitthimeathegorn, O., et al. Direct and Indirect Effects of Blue Light Exposure on Skin: A Review of Published Literature. Skin Pharmacol Physiol. (2022, August 31).

Donna McIntyre is a board-certified nurse practitioner at Curology. She obtained her Master of Science in Nursing at MGH Institute of Health Professions in Boston, MA.

* Subject to consultation. Subscription is required. Results may vary.

Written by

Curology Team

Medically reviewed by

Donna McIntyre, NP-BC