How long does it take to get sunburned?
Between about 12 minutes and 2 hours, depending on two things: the UV index and your skin type. At UV index 10, a common midday number in US summers, fair skin starts to burn in about 17 minutes. At UV index 3, the same skin takes about an hour. Darker skin takes longer, but it still burns, and it still takes UV damage before it shows.
The chart below shows the estimated minutes until your skin turns just pink with no sunscreen. A real burn, the painful kind, takes about two to three times as long. Don't aim for the number. It's the point where damage becomes visible, not where it starts.
UV index sunburn time chart
| UV index | Type I | Type II | Type III | Type IV | Type V | Type VI |
|---|---|---|---|---|---|---|
| 3 (Moderate) | 44 min | 56 min | 1 h 7 min | 1 h 29 min | 2 h 13 min | 3 h 42 min |
| 4 (Moderate) | 33 min | 42 min | 50 min | 1 h 7 min | 1 h 40 min | 2 h 47 min |
| 5 (Moderate) | 27 min | 33 min | 40 min | 53 min | 1 h 20 min | 2 h 13 min |
| 6 (High) | 22 min | 28 min | 33 min | 44 min | 1 h 7 min | 1 h 51 min |
| 7 (High) | 19 min | 24 min | 29 min | 38 min | 57 min | 1 h 35 min |
| 8 (Very high) | 17 min | 21 min | 25 min | 33 min | 50 min | 1 h 23 min |
| 9 (Very high) | 15 min | 19 min | 22 min | 30 min | 44 min | 1 h 14 min |
| 10 (Very high) | 13 min | 17 min | 20 min | 27 min | 40 min | 1 h 7 min |
| 11+ (Extreme) | 12 min | 15 min | 18 min | 24 min | 36 min | 1 h 1 min |
Minutes with no sunscreen until skin is just visibly pink. Skin types: I very fair, II fair, III medium, IV olive, V brown, VI deeply pigmented. Types V and VI have the least research behind them, so treat those columns as rough.
How the calculator works
The UV index is not a vague "strength" score. It's a measured amount of burning UV. The World Health Organization defines each point on the scale as a fixed dose, so UV index 8 delivers eight times the burning UV of UV index 1, every minute you're out in it.
Your skin type sets how much of that dose it takes to turn pink. Dermatologists call this the minimal erythema dose. We use the low end of the usual range for each skin type, so the calculator leans toward burning sooner rather than later. Research from King's College London found skin type IV needs only about twice the dose of type I, and that people of the same skin type vary a lot. If you know you burn fast, pick the lighter type.
When you search for your city, the tool pulls today's hour-by-hour UV forecast and adds up your dose hour by hour. That matters: heading out at 9 a.m. for three hours is a very different day from heading out at noon.
How long can you stay in the sun with SPF 30 or SPF 50?
You'll often see the rule "burn time × SPF." If you burn in 20 minutes, SPF 30 gives you 600 minutes. That math only works in a lab, where testers apply 2 mg of sunscreen per square centimeter of skin. That's about a shot glass for your whole body, or 1/4 teaspoon for your face and neck.
Real people use much less. Studies put the usual amount at 0.4 to 1 mg/cm². A 2007 study from Copenhagen found that the drop isn't gradual. At half the lab amount, SPF falls to roughly its square root. At a quarter, it falls to roughly its fourth root.
| Label SPF | Generous (lab amount) | Typical (about half) | Thin (about a quarter) |
|---|---|---|---|
| SPF 15 | Acts like SPF 15 · 5 h 13 min | Acts like SPF 4 · 1 h 21 min | Acts like SPF 2 · 41 min |
| SPF 30 | Acts like SPF 30 · 10 h 25 min | Acts like SPF 5 · 1 h 54 min | Acts like SPF 2 · 49 min |
| SPF 50 | Acts like SPF 50 · 17 h 22 min | Acts like SPF 7 · 2 h 27 min | Acts like SPF 3 · 55 min |
| SPF 70 | Acts like SPF 70 · 24 h 18 min | Acts like SPF 8 · 2 h 54 min | Acts like SPF 3 · 1 h |
Times are for fair skin (type II) at UV index 8, before reapplying. Two things stand out. First, how much you apply matters more than the number on the bottle: SPF 30 applied generously beats SPF 70 applied thin. Second, a higher SPF does help people who under-apply, which is most of us. That's one reason dermatologists like SPF 50 for beach days.
How often to reapply sunscreen
- Every 2 hours outdoors. This is the FDA and American Academy of Dermatology rule, and it's the same for SPF 15 and SPF 100. Sunscreen rubs off, sweats off and breaks down in sunlight.
- Every 40 or 80 minutes in water or heavy sweat. "Water resistant" on a US label must say 40 or 80 minutes. Nothing is waterproof.
- Right after towel drying. A towel wipes off a big share of what's left.
- A second coat 15 to 30 minutes in. This one surprises people. A UK modeling study found that reapplying early, around 20 minutes after going out, cuts total UV exposure more than waiting the full 2 hours, because it covers missed spots and tops up a thin first layer. A Danish review gave simpler advice: apply before you go out, then reapply once within the first hour.
The calculator builds this schedule for you. Pick your start time, how long you'll be out and whether you'll be in the water.
When sunscreen alone isn't enough
If the calculator says you'll burn even with sunscreen, believe it. A long beach day at UV 9 or higher can deliver several times your sunburn dose, and a typical coat of SPF 30 only covers part of it. Stack your protection:
- Shade at midday. The FDA advises limiting sun between 10 a.m. and 2 p.m., when rays are strongest. UV peaks around solar noon, which is closer to 1 p.m. during daylight saving time, so check the hourly bars in the tool for your own peak.
- A wide-brim hat and UPF clothing. They don't wash off or need reapplying.
- Sunglasses with UV protection. Eyes burn too.
- Extra care on snow, water and at altitude. Fresh snow reflects up to 80% of UV back at you, according to the WHO, which is why skiers burn under their chins. Tick "On snow" in the tool to account for it. Water and sand reflect less, but a beach umbrella doesn't block reflected UV.
Things that make you burn faster
Some skincare and medicines make your skin more sensitive to sun, so you burn sooner than the chart says.
- Retinoids: tretinoin, adapalene and retinol thin the outer skin layer. Use them at night and wear SPF 30+ every morning. See our retinol guide.
- Exfoliating acids: glycolic and lactic acid (AHAs) increase sun sensitivity, and US labels warn you to wear sunscreen for a week after use. Check how they combine with retinol on our retinol and glycolic acid page.
- Medications: doxycycline, some diuretics and oral acne drugs like isotretinoin can cause severe burns. Ask your pharmacist if your prescription is photosensitizing.
- Recent peels, laser or waxing: fresh skin burns fast. Follow your provider's sun advice.
Common sunscreen mistakes
- Too little. If a 3 oz bottle lasts you all summer, you're under-applying. One full-body coat uses about 1 oz.
- Applying at the beach. Put it on 15 minutes before you go out, so you're covered from the first minute.
- Missing spots. Ears, the back of the neck, the tops of the feet, the scalp part and the lips get missed most.
- Trusting makeup SPF. You'd need a thick layer of foundation to get the SPF on the label. Wear real sunscreen underneath and use a stick or powder SPF to top up.
- Skipping cloudy days. Clouds lower UV, but not always by much. Check the forecast UV, not the sky.
- Using last year's bottle. Sunscreen expires. Check the date with our cosmetic expiry checker.
Not sure which SPF or formula suits your skin? The SPF recommendation quiz picks a type for you, and our guide to how much sunscreen you need shows the amounts for each body area.
When to see a doctor about a sunburn
Most sunburns heal on their own in a week. Get medical care if you have blistering over a large area, fever or chills, dizziness or confusion, or signs of infection. Call your pediatrician if a baby gets sunburned; the FDA advises keeping infants out of the sun between 10 a.m. and 2 p.m. altogether. And if you notice a new or changing mole, book a skin check with a dermatologist.