How Long Unprotected Skin Takes to Burn
Every phototype has its own natural UV tolerance before redness starts.
- 10 min: Type I baseline (placeholder reference value)
- 20 min: Type III baseline (placeholder reference value)
- 60 min: Type VI baseline (placeholder reference value)
- Fitzpatrick: Scale used (six-category skin phototype)
Why baseline time varies by phototype
Melanin density changes how fast unprotected skin reacts to UV.
How SPF Multiplies Your Safe Exposure Window
SPF is a multiplication factor applied to the baseline burn time.
- ~93%: SPF 15 blocks (placeholder UV transmission estimate)
- ~97%: SPF 30 blocks (placeholder UV transmission estimate)
- ~98%: SPF 50 blocks (placeholder UV transmission estimate)
- ~99%: SPF 100 blocks (placeholder UV transmission estimate)
The multiplication principle
Higher SPF numbers block a larger share of incoming UV rays.
Calculating the Extended Safe Sun Window
Baseline time multiplied by SPF gives the theoretical safe window.
- baseline×SPF: Formula (placeholder simplified model)
- SPF30 → 10h: Example type III (placeholder illustrative figure)
- sweat/water: Real-world factor (placeholder caveat note)
- 2h max: Cap applied (placeholder practical limit)
Theoretical vs practical exposure time
Real skin protection is capped well below the raw multiplication result.
Why Sunscreen Must Be Reapplied Regularly
Sunscreen film degrades from sweat, water, and rubbing over time.
- 2 hours: Standard interval (placeholder general guideline)
- immediately: After swimming (placeholder guideline note)
- immediately: After toweling (placeholder guideline note)
- 40-80 min: Water-resistant label (placeholder test duration)
The decay of protective film
Coverage thins unevenly, so a fixed reapplication cycle is safest.
Combining SPF and Phototype into One Safe-Sun Plan
The safest guidance blends SPF strength with individual skin phototype.
- shade + high SPF: Fair skin advice (placeholder guidance summary)
- moderate SPF ok: Dark skin advice (placeholder guidance summary)
- reapply on cycle: Everyone (placeholder guidance summary)
- SPF30+ daily: Best practice (placeholder guidance summary)
Personalizing the safe exposure plan
Combine both sliders to get a realistic personal recommendation.