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Reapplying sunscreen | Why does this matter?

Updated: Jun 12, 2023

The general rule of thumb when it comes to reapplying sunscreen is to reapply every 2 hours, regardless of the SPF listed on the container. If you are sweating or swimming, it may be necessary to reapply more frequently. This may be every 40 or 80 minutes depending on the product used. The water-resistant sunscreens will actually state on the container the duration of time that the product can be effective. There is no such thing as a waterproof sunscreen since every sunscreen will wear off at some point. Read more...

 

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reapplying sunscreen

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Video: Techei



Why is sunscreen application so important and what is the general rule of thumb when it comes to reapplying?



The general rule of thumb when it comes to reapplying sunscreen is to reapply every 2 hours, regardless of the SPF listed on the container. If you are sweating or swimming, it may be necessary to reapply more frequently. This may be every 40 or 80 minutes depending on the product used. The water-resistant sunscreens will actually state on the container the duration of time that the product can be effective. There is no such thing as a waterproof sunscreen since every sunscreen will wear off at some point.


It can be really challenging to figure out when your skin will be at the highest risk of UV exposure since temperatures and light are not good gauges. I was recently in Morocco and while in the Sahara with temperatures up to 110 degrees the UV index did not go above an 8, but in Casablanca with temperatures around 78 degrees and cloudy the UV index was a 10. Probably one of the best ways to determine your risk of UV exposure is by finding the UV index on your smartphone's weather app. The weather app includes the UV index that can help guide your sunscreen application needs.



What are some of the reasons people might not reapply their sunscreen?


There are several reasons why people may not reapply sunscreen. Perhaps the most common reason to not reapply sunscreen is simply not recognizing the need to do so. My patients will often state that they reapply sunscreen when at the beach or the pool but not necessarily otherwise. I believe that most people use the feeling of heat on their skin as the gauge to judge the need to reapply. Remember that UV has no temperature associated with it, however. This means that even if it is cold, the UV may be intense. Consider the fact that one of the most common places to get a sunburn is on ski slopes and not always just at the ocean. The term “sunburn” is misleading simply because it implies heat from the sun triggers a burn and people assume this is the damage their skin is experiencing. The real damage is to the DNA of our cells from the UV exposure and a burn may not always be the clinical sign that your DNA is damaged.


Another reason that many people may not reapply sunscreen is the ease of use. If a product is messy, it may be hard to consider reapplying it and risking ruining your clothes!



Not having sunscreen with you will of course make it challenging to reapply. If you apply sunscreen at home and do not carry it with you, there is a chance you may find yourself outdoors in need of a reapplication but not have the product readily available to do so!



Do I really have to reapply sunscreen if I plan to be indoors?


This is a frequent question I receive and an important one to address. After all, I work indoors for the entire stretch of peak sunlight. Do I reapply sunscreen? The answer is no unless I plan to spend time outdoors for other reasons. There is a study by Rungananchai et al that evaluated sunscreen effectiveness after 8 hours for indoor workers. This study determined that sunscreen maintained reasonable effectiveness after 8 hours if it was applied adequately in the morning. The key to remember is that working indoors means staying indoors. If during the course of the workday, you may be in your car, spend time outside walking or eating, are situated close to windows that may not block UV, your workday ends during peak sunlight hours, or you plan to sweat or swim, you may need to consider a reapplication.



Are sunscreen sticks, powders, and compact sprays good options for reapplication? If so can you recommend any specific brands?



I am personally a fan of sticks and sprays for application. For faces, it can be easy to take a sunscreen stick and simply smear it around like you would a lip balm on your lips. This reduces the time needed to rub in the product as well as ensures adequate coverage with minimal application time. I tend to keep Neutrogena Pure and Free Baby with me for that reason. I like that it's a zinc-containing product and rubs on easily.


For the body, a quick reapplication with a spray is a great way to get fast efficient coverage when needed. I’m a fan of La Roche Posay Ultralight Sunscreen Spray. It has nice coverage, sprays evenly, and has a nice stream from the canister that does not seem to carry off with the wind as easily as some products.




Reapplying sunscreen

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