An essential part of every skincare regimen 365 days a year, rain or shine, sunscreen helps protect the skin from damaging UV rays. Read on to learn more about the benefits of sunscreen and answers to common questions such as “How does sunscreen work?”, “How long does sunscreen last?” and “Does sunscreen expire?”

The benefits of sunscreen

The main benefits of sunscreen when using a broad spectrum sun protection product is helping to protect the skin from UVA and UVB rays and minimize the damage that can lead to early signs of skin aging and skin cancer when used as directed with other sun protection measures2. In addition, sunscreen products can be specially-formulated to provide other benefits to the skin, such as extra moisture, and may contain beneficial ingredients such as soothing niacinamide  and ceramides to help restore the skin’s natural protective barrier.

However, it is important to keep in mind that although effective for helping to protect the skin from UV rays, sunscreen alone is not enough6, especially when at the beach, by the pool or spending a significant amount of time outside. For comprehensive sun protection, it’s best to wear protective clothing (including a hat and sunglasses), seek shade when possible and avoid direct sun exposure during mid-day hours.1

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How does sunscreen work?

Sunscreen products are designed to help prevent sunburn2, and broad spectrum protection is essential to help shield skin from UVA and UVB rays. When UV rays enter the skin, they disrupt the cells’ normal growth and function, as well as break down the skin’s collagen and elastin (which leads to lines and wrinkles).7

Sunscreens work in two ways, depending on the UV filter ingredients8 found in a sun protection product. Sunscreens with chemical-based ingredients such as homosalate work by sinking into the top layers of the skin and absorbing UV radiation before it can damage skin cells. Mineral (also called physical) sun filters, like zinc oxide and titanium dioxide, create a barrier on the skin’s surface that reflects UV rays off the skin. Some sun protection products include a mix of both chemical and mineral sun filters.1

How long does sunscreen last?

The recommended amount of sunscreen required to protect the entire body is one ounce (or a shot-glass sized amount). Once applied, sunscreen is effective for up to two hours—or  less when swimming, sweating  or toweling off—which is why it’s important to reapply9 after these activities or at least every two hours. A water-resistant sun protection product will be labeled as effective for up to 40 or 80 minutes before it must be reapplied. It is essential to use any sun protection product as directed.2

This also leads to the question, Does sunscreen expire?10 Yes, it does, which is why there is an expiration date on the packaging. But with this in mind, sunscreens are often left exposed to sunlight and extreme heat for hours at a time, which can reduce their effectiveness well before the expiration date. This is why it’s important to protect the product from excessive heat and direct sun.2

  1. https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs
  2. Baumann, L. (2009) Cosmetic Dermatology: Principles and Practice (pp.245-254). New York: McGraw-Hill Medical
  3. https://www.aad.org/public/spot-skin-cancer/learn-about-skin-cancer/prevent/how-to-apply-sunscreen
  4. https://www.aad.org/media/news-releases/study-most-americans-don-t-use-sunscreen
  5. https://www.skincancer.org/skin-cancer-information/skin-cancer-facts#general
  6. https://www.cdc.gov/cancer/skin/basic_info/sun-safety.htm
  7. Biniek, K., Levi, K., Dauskardt, R. H. (2012). Solar UV radiation reduces the barrier function of human skin. Proceedings of the National Academy of Sciences of the United States of America, 42, 17111-17116
  8. https://www.aad.org/public/spot-skin-cancer/learn-about-skin-cancer/prevent/say-yes-to-sun-protection
  9. https://www.webmd.com/children/sunscreen-use-correctly
  10. https://www.mayoclinic.org/healthy-lifestyle/adult-health/expert-answers/sunscreen-expire/faq-20057957