How long in the sun
How long in the sun for vitamin D with fair skin
You need the least of anyone. The usual advice overshoots for you, and the cost of overshooting is a burn.
Between 5 and 15 minutes, depending on the month.
The dose you need and the dose that hurts are close together
Fair skin has little melanin to absorb ultraviolet, so it makes vitamin D quickly — and reddens quickly for the same reason. In midsummer the gap between having enough and starting to burn is a matter of minutes, not hours. The advice that circulates was written around a darker default, so following it costs you nothing in vitamin D and buys you sun damage you did not need. Cumulative ultraviolet exposure is the main modifiable cause of skin cancer, and fair skin carries the highest baseline risk, which makes the short answer the safe one rather than the lazy one.
Fitzpatrick I and II: skin that always burns and never tans, or burns easily and tans a little.
What these numbers assume
- 25% of your skin uncovered — roughly arms and face
- age 35, because synthesis slows as skin ages
- a target of 1000 IU in one session
- latitude 40°, clear sky, at sea level
1000 IU is this tool's choice, not a settled consensus: national bodies recommend anywhere from 600 to 2000 IU a day, and which one you pick changes every number on this page.
Month by month
The quickest and slowest of the band, on the strongest and weakest day of each month.
- January: not possible at any length of exposure
- February: 12–20 min
- March: 8–15 min
- April: 6–10 min
- May: 5–7 min
- June: 5–6 min
- July: 5–6 min
- August: 5–8 min
- September: 6–11 min
- October: 9–19 min
- November: 15–20 min
- December: not possible at any length of exposure
The months when no amount of sun works
At this latitude the sun does not climb high enough in January, December. That is not a matter of staying out longer: below a UV index of 3 the wavelength that makes vitamin D barely reaches the ground at all, so the answer is the same at five minutes and at five hours.
How this compares with burning
On the strongest day of the season you need about 5 min, against roughly 21 min to reach visible redness. The vitamin D is done long before the damage starts — which is the point: there is nothing to gain by staying out until you burn.
The six types in detail
- Type 1: 5–12 min
- Type 2: 6–15 min
- Type 3: 7–18 min
- Type 4: 11–27 min
- Type 5: 19–45 min
- Type 6: 30–72 min
Not your skin?
The band the generic advice was written for, unlabelled.
Type 3–4: 7–27 min
Several times longer, and the season closes earlier than the calendar suggests.
Type 5–6: 19–72 min
Where the numbers come from
Solar elevation is computed for each day of the year, the UV index from it using the Madronich model with van Heuklon's ozone column, and the exposure time from Holick and Dowdy (2010) with the photodegradation ceiling that makes long sessions stop paying. Nothing here is typed in by hand — change the model and this page changes with it.
This is an estimate for a clear sky at a stated latitude, not medical advice, and it cannot know your skin, your medication or your blood levels. If you think you are deficient, that is a question for a doctor and a blood test, not for a calculator.