The short answer: the burn-time table
These are the approximate minutes to the first signs of mild sunburn for unprotected, unconditioned skin, by Fitzpatrick type and UV level. It's the same model UV Buddy runs live — except the app uses your exact UV right now, not a range.
| Skin type | Low (UV 1–2) |
Moderate (UV 3–5) |
High (UV 6–7) |
Very high (UV 8–10) |
Extreme (UV 11+) |
|---|---|---|---|---|---|
| Type I | 60 min | 25 min | 15 min | 5 min | 4 min |
| Type II | 80 min | 45 min | 20 min | 10 min | 5 min |
| Type III | 120 min | 60 min | 45 min | 30 min | 20 min |
| Type IV | 130 min | 70 min | 50 min | 40 min | 30 min |
| Type V | 240 min | 120 min | 90 min | 60 min | 30 min |
| Type VI | 300 min | 140 min | 120 min | 90 min | 30 min |
Estimates for bare, unconditioned skin at sea level — from the same model UV Buddy runs live. SPF multiplies these times; reflection, altitude and medications shrink them.
What the Fitzpatrick scale actually is
In 1975, dermatologist Thomas Fitzpatrick classified skin into six phototypes based on how it responds to UV — not how it looks indoors, but what it does in the sun:
- Type I — always burns, never tans. Often very fair skin, freckles, red or blond hair.
- Type II — burns easily, tans minimally and slowly.
- Type III — burns moderately, tans gradually to light brown. The most common type in the US and Europe.
- Type IV — burns minimally, tans easily to olive or moderate brown.
- Type V — rarely burns, tans deeply and easily.
- Type VI — almost never burns visibly, deeply pigmented skin.
Two people on the same towel at the same beach can have a 5× difference in burn time. That's why generic advice like "limit sun to 20 minutes" is nearly useless — it's dangerously long for a Type I and needlessly cautious for a Type VI.
The math: MED ÷ UV intensity
Dermatology quantifies sunburn with the minimal erythema dose (MED) — the amount of UV energy, in joules per square metre, that produces the first visible reddening of your skin. Typical reference values run from about 200 J/m² for Type I up to 1000 J/m² for Type VI.
The UV index, in turn, is a linear measure of how fast UV energy is arriving right now. Divide one by the other and you get your burn window:
burn minutes ≈ MED ÷ (UV index × 1.5)
Worked example: Type III skin (MED 350) at UV 5 → 350 ÷ 7.5 ≈ 47 minutes to first redness. The table above bakes in exactly this arithmetic per UV band. Double the UV and your window halves — which is why UV 8 afternoons end so many holidays early.
Find your type (the honest way)
Don't guess from a mirror. Answer these the way your skin actually behaves:
- What happens after 30 unprotected minutes of strong summer sun — blistering burn, red then brown, or just brown?
- Do you freckle? Did you as a kid?
- What's your natural hair and eye color?
- How does your skin look in winter — porcelain, cream, olive, brown, deep brown?
- Do burns peel into new burns, or fade into tan?
- Any history of unusual sun sensitivity or reactions?
If you land between two types, round toward the more sensitive one — burning because you flattered yourself is the classic mistake. (UV Buddy's in-app quiz does exactly this: six questions, ties resolved toward the safer type.)
Shadow rule: if your shadow is shorter than you are, the UV is high enough to burn most skin types. Check the number before you settle in.
What changes your real burn time
- SPF — correctly applied sunscreen multiplies your window (SPF 30 ≈ 30× in theory; real-world application is thinner, so treat it as much less and reapply every 2 hours).
- Water, sand and snow — reflection adds up to 25% (water), 15% (sand) or even 80% (fresh snow) extra UV on top of the index.
- Altitude — roughly +10% UV per 1000 m. A UV 6 forecast in the valley can behave like UV 8 on the mountain.
- Medications — some antibiotics, retinoids and diuretics are photosensitizing. Check the leaflet.
- Existing tan — a real tan adds modest protection (roughly SPF 2–4), far less than people assume.
Your burn window, computed live
UV Buddy runs this exact MED model against the real UV index at your location, minute by minute. Take the six-question quiz once, and every timer, tan session and alert is sized to your skin — not a generic average.
Mini-FAQ
Can my skin type change?
Your phototype is genetic and stable. What changes seasonally is your current melanin level and conditioning — which shifts your practical tolerance a little, not your type.
Is a burn time of 0 possible?
At extreme UV with Type I skin, meaningful damage starts in under 5 minutes — effectively "before you find your towel." That's what "extreme" means on the scale.
Does darker skin need sunscreen at all?
Yes. Types V–VI burn far more slowly, but UV still drives photoaging and skin-cancer risk — and burns at UV 11+ happen in half an hour even for Type VI.
UV Buddy is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If you're worried about a burn, mole, or skin reaction, see a qualified clinician. Sources: Fitzpatrick TB (1988), Arch Dermatol; WHO Global Solar UV Index guidance.
Know your number before the sun does
Six questions to find your skin type — then live burn windows, sunscreen alarms and guided tan sessions, sized to you.
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