Fitzpatrick Skin Types (I–VI), Melanin, and Sun Exposure Time
Content last reviewed: October 2026
Developed in 1975 by Harvard dermatologist Dr. Thomas B. Fitzpatrick, the Fitzpatrick skin phototype scale classifies human skin into six types (I through VI) according to constitutive pigmentation (baseline melanin content) and how the skin responds to ultraviolet radiation — specifically its tendency to burn (erythema) versus tan (melanogenesis).
1. How Melanin Competes with 7-Dehydrocholesterol for UV-B Photons
Eumelanin in the upper layers of the epidermis acts as a natural broadband optical filter. It absorbs and scatters incoming UV-B and UV-A photons before they reach the basal and spinous layers where DNA and 7-dehydrocholesterol reside. This provides vital natural photoprotection against DNA damage and sunburn — raising the Minimal Erythemal Dose (MED) from roughly 200 J/m² in Type I skin to 1,000 J/m² in Type VI skin. At the same time, because fewer UV-B photons reach the 7-DHC precursor per minute, darker skin requires more exposure time to synthesize the same quantity of previtamin D3 (though observational studies show the actual difference in vivo is somewhat smaller than the 5× ratio of MED values because melanin sits primarily above part of the epidermal synthesis layer).
2. Fitzpatrick Scale Reference Table (MED, Targets & Exposure Times)
The table below summarizes the standard Minimal Erythemal Dose (1 MED) used in VitaminDcalc for each phototype, the Holick vitamin D target (0.25 MED), the safety ceiling (0.80 MED), and the estimated exposure time at constant UVI 6 with 25% of the body surface uncovered (baseline age ≤ 20 / age 30 in parentheses, normal BMI).
| Phototype | 1 MED (J/m²) | 0.25 MED Target | 0.80 MED Limit | Time at UVI 6 (≤20y / 30y) |
|---|---|---|---|---|
| Type I: Pale white, always burns | 200 J/m² | 50 J/m² | 160 J/m² | ~14 min (~16 min) |
| Type II: White, burns easily | 250 J/m² | 62.5 J/m² | 200 J/m² | ~18 min (~20 min) |
| Type III: Light brown, burns moderately | 300 J/m² | 75 J/m² | 240 J/m² | ~21 min (~24 min) |
| Type IV: Moderate brown, rarely burns | 450 J/m² | 112.5 J/m² | 360 J/m² | ~32 min (~36 min) |
| Type V: Dark brown, very rarely burns | 600 J/m² | 150 J/m² | 480 J/m² | ~42 min (~48 min) |
| Type VI: Black, never burns | 1,000 J/m² | 250 J/m² | 800 J/m² | ~70 min (~80 min) |
3. How to Choose Your Skin Type Safely
Phototype depends on how your untanned skin reacts to the first 30–45 minutes of summer midday sun, not just on hair or eye color. If you are unsure between two adjacent types (for example, Type II vs. Type III), selecting the lighter type is the more conservative choice for preventing sunburn, while individuals with darker skin living at middle or high latitudes should pay special attention to the “vitamin D winter” when low UV-B levels make it difficult to reach higher MED targets through sunlight alone.
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