Water Resistant Sunscreen, Explained: What the FDA's 40 and 80 Minute Claims Test, Why Waterproof Is Banned, and What the Label Tells You to Do Next

The only two claims the FDA allows

Sunscreens sold in the US are regulated as over-the-counter drugs, and the water-resistance rule sits in 21 CFR 201.327. A product may say "Water Resistant (40 minutes)" or "Water Resistant (80 minutes)" on its front panel, and nothing in between. If a sunscreen has not been tested, it cannot make either claim.

Words that are banned

The same rule bars three terms: "waterproof," "sweatproof," and "sunblock." The FDA says these claims overstate what a sunscreen does, because every sunscreen eventually comes off. A product using those words is considered misbranded, so treat them as a sign of an outdated or non-US label.

How the 40 minute test works

Testers apply the product to volunteers, wait, then follow a fixed sequence: 20 minutes of moderate activity in water, followed by 15 minutes of rest out of the water, with the test site not toweled. That cycle repeats once, and the skin then dries completely without toweling before the sun protection factor (SPF) is measured. The 40 minutes counts the time spent in the water, not the clock time of the whole session.

How the 80 minute test differs

The 80 minute claim uses four 20-minute water periods separated by three 15-minute rests, again with no toweling and a full air dry before measurement. A product that holds up through four immersions can carry the longer claim. One that passes only the shorter test carries the 40 minute claim.

Why the SPF on the label is the post-water number

For a product with a water-resistance claim, the labeled SPF is the value measured after the immersion, not before it. That means the number already accounts for the water test. It does not mean the protection lasts for the full 40 or 80 minutes of real use. It means the product kept that rated SPF when measured at the end of the standard sequence.

What the label tells you to do

Water-resistant products must carry reapplication directions: reapply after 40 or 80 minutes of swimming or sweating (matching the claim), immediately after towel drying, and at least every 2 hours. A sunscreen without the claim must say to reapply at least every 2 hours and to use a water-resistant sunscreen if swimming or sweating. The towel instruction matters because the test itself skips toweling, so rubbing is outside what the claim covers.

What the claim does not cover

The test uses a standardized dose, and real application is often thinner, as our sunscreen dose guide explains. It also cannot reflect surf, hot tubs, or hard sweating. Layering over makeup adds another gap, covered in our reapplication over makeup article. For sprays, see the spray sunscreen explainer.

Reading a bottle quickly

Look on the front panel for "Water Resistant (40 minutes)" or "(80 minutes)," then check the Drug Facts directions for the matching reapply line. Remember that Korean sunscreens often add a UVA grade, explained in our PA rating guide, but a PA grade says nothing about water resistance. If the wording on a bottle differs from the US phrasing, the product may follow another country's rules, so read its own directions.

This article is educational, not medical advice. Patch-test any new product on a small area first, and consult a dermatologist about burns, rashes or concerns about sun exposure. Source: FDA, 21 CFR 201.327 and the agency's sunscreen requirements Q&A, checked October 2026.