You put on a water-resistant sunscreen, swim for half an hour, climb out with your skin still beading water, and assume you are covered. Sometimes you are. Often you are less protected than the label suggests, not because the rating is false, but because a real swim is harder on sunscreen than the test that earned it. The label terms themselves are explained in waterproof vs. water-resistant sunscreen. This guide looks at what happens once you actually get in the water.
A water-resistant rating means the sunscreen kept its labeled SPF after 40 or 80 minutes in a controlled indoor test pool.
Real swims add toweling, salt or chlorine, friction, sand and longer sessions, and the test does not account for most of them.
Water-resistant sunscreen does survive a swim, but only if you apply enough and reapply on the label’s schedule.
The short version: the 40 or 80 on the label is a fair comparison between products, not a guarantee for every swim. How you apply and reapply decides the rest.
How is water resistance tested?
The test is set out in the FDA’s sunscreen regulations. Volunteers have the sunscreen applied at a standard thickness, then get into an indoor fresh-water pool or whirlpool kept between 23 and 32°C (about 73 to 90°F). For a 40-minute rating, they do 20 minutes of moderate activity in the water, rest out of the water for 15 minutes without toweling, then do another 20 minutes. For an 80-minute rating, the cycles continue until they have spent 80 minutes in the water. The skin is left to air dry, again without a towel, and the SPF is measured. If the product still delivers its labeled SPF, it earns the rating.
What does the test leave out? The conditions are controlled on purpose, so results are comparable between products. That also means the test does not include towels, salt water, chlorine at pool levels, waves, sand, wetsuits, goggle straps or sessions longer than 80 minutes.
What actually strips sunscreen during a swim?
Towel drying. This is the big one. The test avoids toweling because rubbing removes sunscreen physically, which is why every water-resistant label tells you to reapply immediately after towel drying.
Not enough to begin with. SPF is tested at 2 milligrams per square centimeter of skin, and most people apply far less, so they start the swim with less protection than the label number. Sunscreen 101: your guide to SPF covers how much is enough.
Friction. Wetsuit collars, rash guard edges, goggle straps, swim caps, boards and sand all wear sunscreen off in specific spots, often exactly where swimmers find their burns. Goggles also leave their own marks, covered in our guide to goggle marks.
Sessions longer than the rating. An open-water swim, a long surf session or a full swim meet can easily run past 80 minutes. Past that point, the label makes no promise at all.
Salt and chlorine. The test uses fresh water, so it does not measure performance in the ocean or a chlorinated pool. Both also dry out and irritate skin over a long season, part of why swimmers deal with chlorine rash and chlorine-dried skin.
Pool, open water and surf: what changes?
Pool swimming. The setting closest to the test. The risks are long practices or meets, repeated toweling between events and time on the deck in full sun. Reapply each time you get out and dry off. Our swimming sunscreen guide covers what to look for.
Open water and triathlon. Long continuous sessions, often in a wetsuit that rubs the neck and arms. Apply generously before the wetsuit goes on, cover the back of the neck, and reapply in transition if you can. Sweat on the bike and run then takes over, and a formula that drips into your eyes becomes a problem. Here is why that happens.
Surf, paddle and beach days. Reflected light off the water, sand, salt and wax all add up, and sessions rarely stick to a clock. Rash guards and hats do a lot of the work, with sunscreen on everything they leave exposed.
How to make water-resistant sunscreen last
Apply to dry skin, before you get wet. Put it on 15 minutes before you swim so it has time to set.
Use enough. About a shot glass for the whole body, and a generous layer on the face, ears and back of the neck. Do not miss the tops of the feet, the hairline and the edges of your swimsuit.
Reapply on the label’s schedule, not by feel. After 40 or 80 minutes in the water, immediately after toweling, and at least every two hours. Beading water is not proof the sunscreen is still working.
Pat, do not rub. Blot your face and body when you get out instead of scrubbing with a towel, then reapply anyway.
Cover up where you can. A rash guard, swim cap and shade between sessions reduce how much depends on sunscreen alone.
Check the date. A bottle that has spent summers in a hot swim bag ages faster. Here is how to tell if yours still works.
Mineral or chemical for swimming? Both can earn an 80-minute rating, and the rating matters more than the filter. Many swimmers prefer mineral because it tends to sting the eyes less and stays stable in strong sun. The full trade-off is in mineral vs. chemical sunscreen for athletes, and what makes a mineral formula hold up in water is in what the best mineral sunscreens have in common [add link once published]. Water-resistant (80 minutes) options for face and body are in our sunscreen collection.
After the swim
Water-resistant sunscreen is built to hold on, so water alone will not remove it all. Wash it off with a gentle cleanser, rinse off chlorine or salt promptly, and follow with a moisturizer to support your skin barrier. Cleansers and moisturizers for that routine are in our recovery skincare collection. If chlorine smell lingers, see how to get chlorine smell out of skin.
The takeaway
Water-resistant sunscreen does survive a swim, within the limits of how it was tested. The 40 or 80 on the label was earned in an indoor fresh-water pool, with a full layer applied and no towels involved. Real swims add toweling, friction, salt, chlorine and longer sessions. Close the gap by applying enough to dry skin before you get in, reapplying on the label’s schedule and after every towel-off, and letting clothing and shade do part of the work.
References
- U.S. Code of Federal Regulations. 21 CFR § 201.327: Over-the-Counter Sunscreen Drug Products; Required Labeling and Testing
- U.S. Food and Drug Administration. Labeling and Effectiveness Testing; Sunscreen Drug Products for Over-the-Counter Human Use; Final Rule. Federal Register, 2011.
- King’s College London. Sunscreen Users Receive Less Than Half the Sun Protection They Think. Acta Dermato-Venereologica, 2018.
- American Academy of Dermatology. How to Apply Sunscreen
- U.S. Food and Drug Administration. Sunscreen: How to Help Protect Your Skin from the Sun
Read next: Waterproof vs. Water Resistant Sunscreen: What's the Difference? · Best Water-Resistant Sunscreen for Swimming: A Dermatologist's Guide · Chlorine Rash: A Dermatologist's Guide to Treatment and Prevention
