Skin types: how long until sunburn?

Raydrop · July 19, 2026

Two people standing side by side, under the same sun, at the same time: one turns pink in twenty minutes, the other cruises through the whole afternoon. That's not luck, it's skin type. It's exactly why Raydrop asks for yours the moment you set up a profile: without it, a single alert threshold means nothing for the whole crew.

The Fitzpatrick scale, in short

Skin type sorts sun sensitivity on a scale from I to VI, fairest to darkest. The UV APIs that power sun-tracking apps lean on this exact same scale to estimate safe exposure times per UV index and skin type. In practice, the lower you sit on the scale (very fair skin, fair hair, frequent sunburn, rarely tans), the faster your skin reacts to a given dose of radiation. On the flip side, a higher skin type (deeper skin tone, sunburn is rare) tolerates a longer stretch at the same UV index. Most people land somewhere along that gradient, and recent sun exposure history nudges sensitivity around too.

The six skin types, roughly:

• I: very fair skin, freckles easily, burns almost every time, basically never tans.
• II: fair skin, burns easily, tans a little and gradually.
• III: fair to medium skin, burns moderately, tans fairly steadily.
• IV: olive skin, rarely burns, tans easily and fairly fast.
• V: brown skin, burns very rarely, tans deeply.
• VI: deeply pigmented skin, almost never burns, natural pigmentation offers the best baseline protection of the group.

Time to sunburn: an estimate, not a guarantee

Here's the important part: skin type only gives you an estimate. It says nothing about last night's bad sleep, a photosensitising medication you're taking without thinking about it, or the fact that you already burned the same patch of skin last week, which leaves it more fragile than usual. Raydrop combines your declared skin type with the real UV index of the moment to adjust its reminder pace, but that number stays a cautious guideline, not a medical stopwatch. No app, no sensor, replaces actually paying attention to your own skin while you're out there.

What SPF actually does: it multiplies time, it doesn't excuse reapplying

This is the most common mistake: thinking a high SPF means you can slather up once in the morning and forget sunscreen until evening. A higher SPF protects better while it's on your skin, but that doesn't mean it stays on, or protects, for longer. SPF 50 doesn't last twice as long as SPF 25: it protects better over the same stretch of time, which is a different thing entirely. The dermatological consensus is consistent on this: whether you're wearing SPF 15, 30, or 100, the reapplication schedule stays the same.

Why every two hours

The two-hour outdoor rule isn't an arbitrary convention: it's the benchmark dermatologists settle on, and it accounts for two separate things. First, sunscreen filters degrade with time and with UV exposure itself: the protection wears off chemically, even if you never move off your towel. Second, the layer of sunscreen wears off mechanically: friction from clothes, contact with sand, sweat. Net result, two hours is already a generous ceiling on a dry, low activity day. The moment you swim, sweat, or towel off, reapply sooner: a swim can weaken and all but wash off protection in under an hour, even with a so-called water-resistant formula, which buys time without eliminating the problem.

What Raydrop does with all of this

Raydrop asks for everyone's skin type when their profile gets set up, along with the SPF they normally use. From there, the app cross-references that profile with the real UV index at your location to tighten or loosen the reminder pace: sooner if the index climbs or the profile is sensitive, later if the sky clouds over. The two-hour ceiling stays the default, automatically shortened when you flag activity or a swim in the app. Every member of the crew keeps their own timer: the fairest skin type in the family doesn't set the pace for everyone else, and vice versa.

Apply that same logic to kids, and it gets even more useful, since their skin behaves differently. That's exactly what the last article in this series covers.

Raydrop helps you remember sunscreen; it doesn't replace medical advice. If you're on photosensitising medication or have at-risk skin, ask your doctor.