DermUV

Minimal Erythemal Dose (MED)

MED is the smallest dose of UV that produces visible redness on a given person's skin, measured in J/m².

Minimal Erythemal Dose (MED) explained

MED varies by Fitzpatrick type: Type I ≈ 200 J/m², Type VI ≈ 1000 J/m². It is the reference point used when estimating exposure times. 1 MED is the threshold for sunburn — but DNA damage begins at well below 1 MED, which is why daily SPF matters even on low-UV days.

Related terms

Terms related to Minimal Erythemal Dose (MED) connect the UV and sunscreen topic cluster.

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Continue with reference material and live city UV forecasts.

Context behind Minimal Erythemal Dose (MED)

Burn-time figures come from minimal erythemal dose (MED) values published for each Fitzpatrick skin type, divided by the erythemal irradiance at a given UV index. Personal MED varies by roughly 20 percent, so treat every number as a planning range.

Sunscreen labels are tested at 2 mg/cm². Typical real-world application is closer to half that, so DermUV assumes about half the labelled SPF when it estimates protected time.

Cloud cover is not protection. Thin or broken cloud can still pass most incoming UV, and light cloud edges can briefly scatter more UV toward the ground than a clear sky.

Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.

Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.

UV scale reference

The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.

A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.

Keep exploring DermUV

These pages give more depth around minimal erythemal dose (med), from UV-scale reference material to definitions and city forecasts.

All figures on DermUV are educational estimates built from public UV data and published dose literature. They are not personal advice.