How Often to Reapply Sunscreen By Milan Carter

October 21, 2025

Milan Carter | she/her/hers

Medical Student, UCLA PRIME-LA/Charles R. Drew

David Geffen School of Medicine at UCLA | Class of 2027

So, you’ve found the perfect sunscreen, one that blends seamlessly into your skin, doesn’t leave a white cast, and works well with your skincare routine. That’s a huge win! But now comes the next step: How often should you reapply sunscreen? Yes, you need to reapply your sunscreen!

Many assume that applying sunscreen once in the morning is enough, but that’s not the case. Sunscreen should be applied 15 minutes BEFORE you are exposed to ultraviolet (UV) rays and then reapplied throughout the day to maintain its effectiveness, and we’re here to explain why.

So, you’ve found the perfect sunscreen, one that blends seamlessly into your skin, doesn’t leave a white cast, and works well with your skincare routine. That’s a huge win! But now comes the next step: How often should you reapply sunscreen? Yes, you need to reapply your sunscreen! Many assume that applying sunscreen once in the morning is enough, but that’s not the case. Sunscreen should be applied 15 minutes BEFORE you are exposed to UV rays and then reapplied throughout the day to maintain its effectiveness, and we’re here to explain why.

Why Does Sunscreen Need to Be Reapplied?


I spoke with Dr. Karen Nern, MD, a board-certified dermatologist, who explains that many people underestimate how quickly sunscreen can wear off, stating that sunscreen should be reapplied “Every two hours. Even water-resistant formulas need to be reapplied to maintain their effectiveness.”


Sunscreen is designed to protect your skin from harmful UV rays, which can cause sunburn, premature aging, and skin cancer.1 But it doesn’t last all day. Several factors can cause sunscreen to wear off. Physical activity or heat can lead to sweating, which can degrade the ingredients in sunscreen over time. While water-resistant sunscreen can help to diminish barrier protection during water exposure, it can still degrade with extended exposure and needs to be reapplied.2 Once you get out of the pool or finish your activity, drying off with a towel can remove your sunscreen. If you plan to stay in the sun, make sure to reapply to ensure full coverage. In your day to day, natural skin oils and touching your face can reduce sun protection.

Okay, so I only need to reapply sunscreen if I am outdoors? While it’s true that UVB rays - which cause sunburn - are mostly blocked by windows, UVA rays can still penetrate glass and contribute to premature aging and skin damage.1,3


Additionally, blue light from screens may impact skin health, leading some experts to recommend sunscreen use even indoors. If you work near a window or use screens for long hours, consider reapplying, especially on exposed areas like your face, neck, and hands.


Tips for Reapplying Sunscreen

  1. Choose an SPF 30 sunscreen at least.
  2. Set a reminder to reapply every two hours, especially if you’ll be outdoors.
  3. Find a good makeup-friendly sunscreen to make reapplication easy.
  4. Sunscreen powder, SPF-infused cushion compacts, or spray are some options.
  5. Use water-resistant formulas if you plan to swim or sweat.
  6. Don’t forget your ears, neck, hands, and scalp. These areas are often neglected.


Sunscreen is one of the most important steps in any skincare routine, but applying it once isn’t enough. No matter the weather or the activity, reapplying every two hours is a key habit to keeping your skin healthy and protected. Keep your sunscreen handy, set reminders, and don’t forget to reapply!



Resources:

1. Moore C, Cevikbas F, Pasolli HA, et al. UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling [published correction appears in Proc Natl Acad Sci U S A. 2013 Sep 17;110(38):15502. Ye, Iwei [corrected to Yeh, Iwei]. Proc Natl Acad Sci U S A. 2013;110(34):E3225-E3234. doi:10.1073/pnas.1312933110

2. How to apply sunscreen. American Academy of Dermatology. (n.d.).https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-apply-sunscreen

3. Practice safe sun. American Academy of Dermatology. (n.d.-b). https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/practice-safe-sun

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