What is MED?
MED (Minimal Erythemal Dose) is the smallest amount of UV radiation that produces visible reddening of the skin 24 hours after exposure. Think of it as your skin's threshold — the point where you go from "fine" to "starting to burn."
Everyone's MED is different. Fair-skinned people (Type I) reach their MED much faster than dark-skinned people (Type VI). The UV Index tells you how intense the sun is right now. Together, your skin type and the UVI determine how many minutes you have before burning begins.
Time to burn = MED ÷ UV Index
D-Minder uses this exact formula with your personal skin type and real-time UV conditions to calculate your safe exposure window. The values below are the same ones the app uses — validated over 14 years with 500,000+ users.
MED Values by Skin Type
Type I — Very Fair
Always burns, never tans. Light skin, light eyes, often freckles.
MED 67
Type II — Fair
Burns easily, tans minimally. Fair skin, blue or green eyes.
MED 100
Type III — Medium
Sometimes burns, gradually tans. Cream to light brown skin.
MED 200
Type IV — Olive
Rarely burns, tans easily. Moderate brown skin.
MED 300
Type V — Brown
Very rarely burns, tans darkly. Dark brown skin.
MED 400
Type VI — Dark
Almost never burns. Deeply pigmented dark brown to black skin.
MED 500
Burn Time Chart
Estimated minutes until first visible reddening (MED ÷ UVI). D-Minder applies an additional 20% safety margin — your session will end before you reach these times.
| Skin Type |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| I — Very Fair 67 |
67 | 34 | 22 | 17 | 13 | 11 | 10 | 8 | 7 | 7 | 6 | 6 | 5 | 5 | 4 |
| II — Fair 100 |
100 | 50 | 33 | 25 | 20 | 17 | 14 | 13 | 11 | 10 | 9 | 8 | 8 | 7 | 7 |
| III — Medium 200 |
200 | 100 | 67 | 50 | 40 | 33 | 29 | 25 | 22 | 20 | 18 | 17 | 15 | 14 | 13 |
| IV — Olive 300 |
300 | 150 | 100 | 75 | 60 | 50 | 43 | 38 | 33 | 30 | 27 | 25 | 23 | 21 | 20 |
| V — Brown 400 |
400 | 200 | 133 | 100 | 80 | 67 | 57 | 50 | 44 | 40 | 36 | 33 | 31 | 29 | 27 |
| VI — Dark 500 |
500 | 250 | 167 | 125 | 100 | 83 | 71 | 63 | 56 | 50 | 45 | 42 | 38 | 36 | 33 |
These are estimates. Individual sensitivity varies based on medications, recent UV exposure, altitude, reflection from water/sand/snow, and time of day. When in doubt, err on the side of less exposure. D-Minder uses your actual real-time conditions for the most accurate personalized burn warning.
How D-Minder Uses MED
When you start a sun session, D-Minder calculates your estimated burn time using your skin type's MED value divided by the current UV index at your location. It then applies a 20% safety margin — your burn warning fires at 80% of the calculated time.
For example, if you're Type II (MED 100) and the UV index is 8:
- Burn time: 100 ÷ 8 = 12.5 minutes
- Safe exposure (80%): 10 minutes
- D-Minder warns you at 10 minutes and reminds you to turn over or seek shade
The science: MED values are based on the Fitzpatrick skin type classification system, developed by Harvard dermatologist Thomas Fitzpatrick in 1975. D-Minder's specific MED values have been validated with Solarmeter UV measurements and refined through 14 years of real-world use by over 500,000 users.
UV Index Scale
The UV Index (UVI) is a standardized measure of UV radiation intensity at the Earth's surface, developed by the World Health Organization.
1-2
Low
3-5
Moderate
6-7
High
8-10
Very High
11+
Extreme
What Happens After MED?
A common question: if I stay out past my MED time, do I keep producing vitamin D?
The answer is nuanced. Vitamin D production in your skin follows a photodegradation curve:
Before MED (~first 15-20 minutes in high UV): Your skin converts 7-dehydrocholesterol (7-DHC) into previtamin D3 at full speed. This is when you're producing the most vitamin D.
After MED: UV radiation begins converting previtamin D3 into inactive photoproducts — lumisterol and tachysterol. Production doesn't stop completely, but drops to roughly 15% of the pre-MED rate. This is your body's built-in safety mechanism against vitamin D toxicity.
The skin can only convert approximately 15% of available 7-DHC into previtamin D3. Once that threshold is reached, further UV exposure drives the photochemical equilibrium toward inactive products rather than more vitamin D.
This is why D-Minder tracks MED: The app calculates your full production rate before MED and the reduced rate (15%) after. Staying out longer than your MED produces diminishing returns for vitamin D while increasing your sunburn risk. The optimal strategy is to get your vitamin D dose within your MED window, then cover up or apply sunscreen.
This photodegradation mechanism was first characterized by Dr. Michael Holick in 1989, showing that "sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation." It's the reason you cannot get vitamin D toxicity from sun exposure alone — no matter how long you stay out.
References
- Fitzpatrick TB. The validity and practicality of sun-reactive skin types I through VI. Arch Dermatol. 1988;124(6):869-871. PubMed
- Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281. PubMed
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930. PubMed
- World Health Organization. Ultraviolet radiation and the INTERSUN Programme — UV Index. WHO
- Sachdeva S. Fitzpatrick skin typing: applications in dermatology. Indian J Dermatol Venereol Leprol. 2009;75(1):93-96. PubMed
- McKenzie RL, Liley JB, Björn LO. UV radiation: balancing risks and benefits. Photochem Photobiol. 2009;85(1):88-98. PubMed
- Webb AR, Engelsen O. Calculated ultraviolet exposure levels for a healthy vitamin D status. Photochem Photobiol. 2006;82(6):1697-1703. PubMed
- Holick MF, et al. Sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation. J Clin Invest. 1989;84(5):1527-1531. PubMed
- Webb AR, et al. The action spectrum for vitamin D3: initial skin reaction and prolonged exposure. Photochem Photobiol Sci. 2016;15(7):896-909. PubMed
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