Reapply sunscreen, or sunblock as many people still call it, at least every 2 hours, and sooner if you swim or sweat. A water-resistant label spells out the sooner: reapply after the 40 or 80 minutes of swimming or sweating it claims, immediately after towel drying, and at least every 2 hours, whichever comes first.
Those lines come from the federal sunscreen labeling rule, 21 CFR 201.327, which sets the Directions on sunscreens labeled under it. A higher SPF (sun protection factor, the number on the front) does not stretch them: the FDA says SPF relates to the "amount of solar exposure," not to time. The same Directions tell you when to start, too: apply "15 minutes before sun exposure."
This page covers US labels: how often and when to reapply, how long sunscreen lasts on skin, how early to put it on, how much to use, and how to reapply. It quotes the labeling rule, the FDA's consumer pages and the American Academy of Dermatology (AAD), and every source is listed at the end. The directions on your own sunscreen are the ones to follow.
How often should you reapply sunscreen?
At least every 2 hours, and sooner after swimming, sweating or towel drying if the label is water resistant.
The rule writes two versions of the reapply line: one for sunscreens labeled water resistant, and one for sunscreens that are not.
| What the label says | Which labels carry it | Rule |
|---|---|---|
| “at least every 2 hours” | Sunscreens labeled under the rule, water resistant or not | 201.327(e)(3) and (e)(4) |
| “after 40 minutes of swimming or sweating” or “after 80 minutes of swimming or sweating” | Water-resistant labels; the minutes match the claim on the front | 201.327(e)(3) |
| “immediately after towel drying” | Water-resistant labels | 201.327(e)(3) |
| “use a water resistant sunscreen if swimming or sweating” | Labels that are not water resistant | 201.327(e)(4) |
Whichever trigger comes first applies, and "at least" makes 2 hours the longest gap the label allows. The FDA's own version is the plainest: "Reapply sunscreen at least every two hours, and more often if you're sweating or swimming." It adds that all sunscreens, "whether labeled as water resistant or not, must provide directions on when to reapply."
How often should you reapply sunblock?
On the same schedule: on a US label, sunblock and sunscreen are the same product.
The labeling rule requires a label that "identifies the drug as a 'sunscreen,'" and it lists the other word among the claims that make a sunscreen label false or misleading:
There are claims that would be false and/or misleading on sunscreen products. These claims include but are not limited to the following: “Sunblock,” “sweatproof,” and “waterproof.” These or similar claims will cause the product to be misbranded under section 502 of the FD&C Act (21 U.S.C. 352).
U.S. Government Publishing Office · read word for word on This paragraph names three words a US sunscreen label may not use, and says similar claims are treated the same way.
The FDA's consumer guidance says the same thing in short: products "may not be identified as 'sunblocks'." So whatever name you grew up with, the reapply line is the one in the table above. Our guide to water-resistant sunscreen claims covers the other two words on that list and what a water-resistance claim means instead.
Does SPF 50 mean 50 minutes, or 500?
No. SPF measures how much sun exposure, not how long, so every SPF is reapplied on the same 2-hour clock.
Some people believe that if they normally burn in an hour, an SPF 15 lets them stay out 15 times longer. The FDA says this is "not true," because "SPF is not directly related to time of solar exposure but to amount of solar exposure." How much exposure you get depends on things like the time of day: the sun is stronger at midday than in the early morning or evening.
That rules out three common readings of the number:
- SPF 30 does not mean "reapply every 30 minutes." The number is not a count of minutes, and an SPF 30 label carries the same "at least every 2 hours" line as any other.
- SPF 50 does not mean 500 minutes. Multiplying the SPF by the time it takes you to burn is exactly the calculation the FDA says is not true.
- SPF 50 does not mean "every 80 minutes" either. Eighty minutes is a separate claim, "Water Resistant (80 minutes)," which a label prints on its front panel only when the product has passed the rule's water test (201.327(a)(2)).
The AAD puts it in one line: "high-number SPFs last the same amount of time as low-number SPFs." A higher SPF earns its place another way, set out under how much sunscreen to use.
How long does sunscreen last on skin?
Count on reapplying within 2 hours, and sooner after swimming, sweating or, on a water-resistant label, towel drying.
The FDA's answer is short: "All sunscreens eventually wash off." So the label sets a fixed interval to reapply rather than a number of hours of protection. FDA consumer guidance says products may not claim "protection for more than two hours without reapplying."
Another FDA rule, 21 CFR 310.545(a)(29)(ii), backs this up. An over-the-counter sunscreen cannot promise a number of hours of protection that doesn't match those Directions unless the FDA approves it as a new drug.
If you meant how long a bottle lasts: the FDA says a sunscreen without an expiration date "should be considered expired three years after purchase."
Does the 2-hour clock stop indoors or on a cloudy day?
The label's line is "at least every 2 hours," with no pause in it, so if 2 hours have passed since you put sunscreen on, reapply before you head back out. Clouds do not stop it either: the FDA says "Even on an overcast day, up to 80% of the sun's UV rays can get through the clouds."
When should you reapply after swimming or sweating?
When the label's 40 or 80 minutes are up, and right after you towel off.
The FDA explains what those minutes are: the claims "tell you how much time you can expect to get the labeled SPF-level of protection while swimming or sweating." To use them:
- Find the claim on the front. It reads "Water Resistant (40 minutes)" or "Water Resistant (80 minutes)" (201.327(a)(2)). If neither is there, the label's own advice is to "use a water resistant sunscreen if swimming or sweating."
- Count your time in the water or working up a sweat. Reapply once the label's minutes of swimming or sweating have passed.
- Towel off, then reapply. A water-resistant label says to reapply "immediately after towel drying."
- Keep the 2-hour line either way. Whichever trigger comes first is the one to follow.
The AAD's Sunscreen FAQs say to reapply "after swimming or sweating, according to the directions on the bottle." Our water-resistant sunscreen guide explains what the 40- and 80-minute tests involve.
What happens if you don't reapply sunscreen?
You are more likely to burn.
The AAD says: "People who get sunburned usually didn't reapply, used too little sunscreen, or used an expired sunscreen."
When the FDA finalized the labeling rule in 2011, it summarised two studies behind the 2-hour line. In one, Wright and colleagues found that subjects who reapplied sunscreen "every 1 to 2 hours and after swimming were not sunburned."
In the other, Rigel and colleagues reported that people who reapplied "every two hours or sooner were five times less likely to sunburn" than those who reapplied only after 2.5 hours or longer.
The agency's conclusion was direct: "we will continue to require the 2-hour reapplication timeframe." If the question behind this one is tanning, we cover whether you can tan with sunscreen on separately.
How much sunscreen should you use?
Use it liberally or generously, as the label says, which is more than many people put on.
| Who says it | Amount | For |
|---|---|---|
| AAD (the FDA gives the same figure) | At a minimum, about 1 ounce, “roughly the amount to fill a shot glass” | Skin not covered by clothing, for most adults |
| AAD | At least 1 teaspoon, “about the amount needed to cover the length of your index and middle fingers” | The face |
| The FDA rule’s SPF test, 201.327(i)(4)(iii) | 2 milligrams per square centimeter of skin | The layer the SPF test applies |
The AAD adds that, depending on your body size, you may need more. Those amounts can look large, and the Academy notes that many people apply only 20 to 50 percent of the amount needed to reach the SPF on the label. That is where a higher SPF helps: the AAD says high-SPF sunscreens help "to compensate for this under-application."
If you have seen a "three-finger rule," the AAD's own finger measure is the face teaspoon in the table above, the length of your index and middle fingers. For the body, see how much sunscreen your body needs.
How early should you put sunscreen on?
15 minutes before sun exposure.
Sunscreen labels say to apply it liberally (some say generously) "15 minutes before sun exposure" (201.327(e)(1)(ii)). The FDA gives the reason: "This allows the sunscreen to have enough time to provide the maximum benefit." The AAD's version is "Apply sunscreen to dry skin 15 minutes before going outdoors."
The SPF test itself waits "at least 15 minutes" after applying before the skin is exposed (201.327(i)(4)(iv)).
For a baby, the label's line is "children under 6 months of age: Ask a doctor" (201.327(e)(1)(iv)), and the FDA gives the same advice.
How do you reapply sunscreen, and which spots get missed?
The same way as the first coat: dry skin, a liberal amount, spread evenly.
- Towel off first if you have been in the water, then put the next coat on straight away.
- Use the same liberal amount again, spread evenly over all the skin your clothes leave bare.
- Cover the spots the FDA calls "frequently forgotten": ears, nose, lips, back of neck, hands, tops of feet, along the hairline, and exposed scalp. For lips the FDA suggests an SPF lip balm, and the AAD a lip balm with an SPF of at least 30.
- Over makeup, the AAD notes that some moisturizers and cosmetics have SPF, and that while these are convenient, "sunscreen needs to be reapplied approximately every two hours when you're outdoors." If a second coat rolls up as you spread it, see why sunscreen can pill when you reapply.
For a head-to-toe routine, see how to apply sunscreen to your whole body and the spots people miss.
A simple reapply routine for a day outside
Put it on before you leave, then let a 2-hour reminder do the rest.
- Apply 15 minutes before you go out, the time the label asks for.
- Set a 2-hour reminder on your phone as soon as you put it on, not when you step outside.
- Reapply sooner when the label says so: after its minutes of swimming or sweating, and right after you towel off.
- Add the Sun Protection Measures the label lists (201.327(e)(2)) on a broad spectrum SPF 15+ sunscreen, one that helps "protect against both forms of UV radiation," UVA and UVB, in the FDA's words: limit time in the sun, "especially from 10 a.m.-2 p.m.," and "wear long-sleeved shirts, pants, hats, and sunglasses."
- Keep your sunscreen with you, so the next coat goes on when the reminder does.
Used together, sunscreen and these measures are what the label's Uses line describes: a broad spectrum sunscreen with SPF 15 or higher may say that, "if used as directed with other sun protection measures," it "decreases the risk of skin cancer and early skin aging caused by the sun" (201.327(c)(2)).
Where Solvyn Shield fits
Solvyn Shield, labeled Solvyn Mineral Sunscreen SPF 50, carries the reapply lines the federal rule sets for an 80-minute water-resistant label. Its Directions, as published on DailyMed (NDC 87777-948-00), include:
- "Apply liberally 15 minutes before sun exposure and as needed."
- "Children under 6 months of age: ask a doctor."
- Reapply:
- "after 80 minutes of swimming or sweating"
- "immediately after towel drying"
- "at least every 2 hours"
Shield is dermatologist-formulated, and zinc oxide, at 17.50%, is its only active ingredient. Its front panel states Broad Spectrum SPF 50 and Water Resistant (80 minutes), the longer of the two water-resistance ratings (see the label image).
It comes in sealed 5 mL single-use packets that are easy to carry in a pocket or bag. Rub it in and it disappears into your skin, with no white cast. Every ingredient is listed on its Drug Facts label on DailyMed, and our ingredient guide walks through Shield's own steps.
See Solvyn Shield's sealed 5 mL packets.
Sources
Label
- Solvyn Mineral Sunscreen SPF 50: Drug Facts label on DailyMed. SPL set ID b0a8d028-87d2-4339-8879-c62cbf8415f2, NDC 87777-948-00, effective 15 June 2026: the Directions quoted above, the active ingredient and every inactive ingredient. U.S. National Library of Medicine.
- Label image (Label2.jpg). The principal display panel, which carries "Broad Spectrum SPF 50" and "Water Resistant (80 minutes)".
Regulation
- 21 CFR 201.327: Over-the-counter sunscreen drug products; required labeling based on effectiveness testing. Paragraph (a)(2) sets the two water-resistance statements; (b) the word "sunscreen"; (c)(2) the Uses line; (e)(1) to (e)(4) the Directions, including the reapply lines and Sun Protection Measures; (g) the barred claims; (i)(4) the SPF test's application and waiting period. eCFR, up to date as of 22 October 2026.
- 21 CFR 310.545. Paragraph (a)(29)(ii): extended-wear claims inconsistent with the 201.327 directions. eCFR, up to date as of 22 October 2026.
- 76 FR 35620, 17 June 2011: Labeling and Effectiveness Testing; Sunscreen Drug Products for Over-the-Counter Human Use. The final rule (FR Doc. 2011-14766); its discussion of the 2-hour reapplication direction, with the Wright and Rigel studies, is at 76 FR 35638. Federal Register.
FDA
- Sunscreen: How to Help Protect Your Skin from the Sun. Reapplying, SPF and time, broad spectrum, washing off, when to apply, how much, frequently forgotten spots, expiration and infants. Content current as of 16 October 2026.
- Tips to Stay Safe in the Sun: From Sunscreen to Sunglasses. What the 40- and 80-minute claims tell you, the claims products may not make, and UV through clouds. FDA Consumer Update, content current as of 10 September 2026.
AAD
- How to apply sunscreen. American Academy of Dermatology: amounts for the body and face, lips, and why people get sunburned. Last updated 15 August 2025.
- Sunscreen FAQs. American Academy of Dermatology: SPF and time, under-application, reapplying, applying before going outdoors, and SPF cosmetics. Last updated 11 February 2025.
Brand record
- About Solvyn. The brand record behind "dermatologist-formulated".
All quoted text and figures above were read from these records on 24 October 2026.
A note on scope. This is general guidance on US sunscreen labels, based on sources read on 24 October 2026. It is not medical advice; follow the directions on your own sunscreen.
Solvyn makes Shield. Its full label is published on DailyMed and linked above, so you can check every ingredient yourself.
