Sun exposure, sunburn and vitamin D

This page exists because "I need the vitamin D" is the most common reason people decline sun protection, and the trade is a poor one.

Sunscreen prevents skin cancer and photoaging, and the evidence is strongest for squamous cell carcinoma and for preventing sunburn and actinic damage. The evidence for melanoma is more mixed but there is a randomised trial showing reduced melanoma incidence with regular sunscreen use in adults. Reapplication matters more than the SPF number: an SPF 30 applied properly outperforms an SPF 50 applied thinly, and most people apply a quarter of the quantity used in the testing.

Vitamin D can be obtained without burning. The amount of sun needed for vitamin D synthesis is small and is not the amount that burns — a few minutes of midday exposure for a fair-skinned person is enough, and for many people at high latitude in winter, none is enough and supplementation is the reliable route. The recommendation is to supplement rather than to burn, because the dose-response for vitamin D from sun is capped by the skin's own regulation while the DNA damage from sunburn is cumulative.

Sunburn is a thermal and radiation burn. Cool it, hydrate, take an anti-inflammatory early, and do not apply benzocaine-containing products (a documented risk of a serious reaction) or greasy ointments while the skin is hot. Blistering sunburn over a large area is a burn and should be treated as one.

The measures with the best evidence. Sunscreen, protective clothing, shade, and avoiding the peak UV hours. Hat and sunglasses for the face and eyes. Never a sunbed — the melanoma risk is established, and the "safe tan" claim does not exist.

Vitamin D supplementation. 600-800 IU daily for adults, more for documented deficiency under supervision. Do not mega-dose, because very high intermittent dosing has been associated with increased falls and fractures.

Medication photosensitivity. Some drugs make the skin much more sun-sensitive: tetracyclines (doxycycline notably), fluoroquinolones, amiodarone, some diuretics, isotretinoin, and St John's wort. Anyone on one of these needs to know, and this list interacts directly with the herbal section of this handbook.