Safe sun time by skin type and UV level

By Trung Hieu Lam, developer of UV Tracker · Published 1 September 2026

What "safe sun time" means

"Safe sun time" is how many minutes of unprotected sun exposure stay below your sunburn threshold — the point at which skin starts to redden, known clinically as the Minimal Erythemal Dose (MED). It is not a claim that shorter exposures cause no UV damage at all; UV exposure and skin cancer risk accumulate over a lifetime regardless of whether any single session causes a visible sunburn. Think of the number below as "how long before sunburn risk", not "how long is completely safe".

The tables

Minutes of safe sun time (before sunburn risk), by Fitzpatrick skin type and UV index. Types I–III below; IV–VI follow.

UV index	Type I	Type II	Type III
1	133	167	233
2	67	83	117
3	44	56	78
4	33	42	58
5	27	33	47
6	22	28	39
7	19	24	33
8	17	21	29
9	15	19	26
10	13	17	23
11	12	15	21

UV index	Type IV	Type V	Type VI
1	300	400	667
2	150	200	333
3	100	133	222
4	75	100	167
5	60	80	133
6	50	67	111
7	43	57	95
8	38	50	83
9	33	44	74
10	30	40	67
11	27	36	61

Not sure which type you are? See the learn section for the Fitzpatrick scale, or check the app.

How the numbers are computed

The UV index is defined as erythemally-weighted irradiance in W/m² × 40, so 1 UVI equals 25 mW/m², or 1.5 J/m² of erythemal dose per minute. Safe sun time is simply your skin type's MED divided by that rate:

minutes = MED ÷ (UV index × 1.5 J/m²/min)

The MED values used above, in J/m²: Type I 200, Type II 250, Type III 350, Type IV 450, Type V 600, Type VI 1000 — the standard values from Fitzpatrick's original classification. Worked example: at UVI 8, Type II's MED of 250 gives 250 ÷ (8 × 1.5) ≈ 21 minutes, which is the anchor UV Tracker's own calculation uses.

What changes the number

These tables assume the UV index you're using is accurate for where you're actually standing. Cloud cover, shade, altitude and reflective surfaces like sand, water or snow all move the real figure — often by more than people expect. See what changes the real number, or measure your actual sky with the app's sky scan.

With sunscreen

Sunscreen extends these numbers, in theory, by roughly its SPF factor — but only if applied at the tested thickness and reapplied on schedule, which most people don't do. Try the safe sun time calculator for a rough sunscreen-adjusted estimate, and see SPF, explained for why the label number rarely matches real-world protection.

UV Tracker measures the UV where you stand — sky scan for local conditions, one photo for your skin type, and your safe sun time on one card. Free forever.

References

World Health Organization, Global Solar UV Index: A Practical Guide. Accessed 2026-09-01.
US Environmental Protection Agency, UV Index Scale. Accessed 2026-09-01.
Fitzpatrick TB. "The validity and practicality of sun-reactive skin types I through VI." Archives of Dermatology, 1988.
CIE/ISO 17166:2019, Erythema reference action spectrum and standard erythema dose.

UV forecast data in the app: Open-Meteo.

This article is general information, not medical advice. Sun-exposure estimates are approximations. If you have concerns about your skin, or a history of skin cancer in your family, see a doctor or dermatologist.

UV index	Type I	Type II	Type III
1	133	167	233
2	67	83	117
3	44	56	78
4	33	42	58
5	27	33	47
6	22	28	39
7	19	24	33
8	17	21	29
9	15	19	26
10	13	17	23
11	12	15	21

UV index	Type IV	Type V	Type VI
1	300	400	667
2	150	200	333
3	100	133	222
4	75	100	167
5	60	80	133
6	50	67	111
7	43	57	95
8	38	50	83
9	33	44	74
10	30	40	67
11	27	36	61

UV index	Type I	Type II	Type III
1	133	167	233
2	67	83	117
3	44	56	78
4	33	42	58
5	27	33	47
6	22	28	39
7	19	24	33
8	17	21	29
9	15	19	26
10	13	17	23
11	12	15	21

UV index	Type IV	Type V	Type VI
1	300	400	667
2	150	200	333
3	100	133	222
4	75	100	167
5	60	80	133
6	50	67	111
7	43	57	95
8	38	50	83
9	33	44	74
10	30	40	67
11	27	36	61

UV index	Type I	Type II	Type III
1	133	167	233
2	67	83	117
3	44	56	78
4	33	42	58
5	27	33	47
6	22	28	39
7	19	24	33
8	17	21	29
9	15	19	26
10	13	17	23
11	12	15	21

UV index	Type IV	Type V	Type VI
1	300	400	667
2	150	200	333
3	100	133	222
4	75	100	167
5	60	80	133
6	50	67	111
7	43	57	95
8	38	50	83
9	33	44	74
10	30	40	67
11	27	36	61