When considering the important question of how much sun is safe, it is helpful to know what skin you are wearing! This is an old, but reliable categorisation of skin types, devised by Dr. Thomas Fitzpatrick at Harvard Medical School. Subsequent charts are available, taking account of parent and grand-parent skin types (for instance, if your grandmother was from Mali and your grandfather from Ireland, but you appear to have Type 3 skin, you may not fit perfectly into that group, depending on what you inherited from each). This is a good place to start anyway…
Type 1 skin: extremely fair, pale skin. Eye colour is usually blue or hazel, with red or blonde hair colour. Freckles are common and the sun tends to burn, not tan the skin. Skin cancers are most prevalent in this group and this group includes albinos.
Type 2 skin: fair, with blue eyes. A slight tan from the sun is possible, but these people burn easily. Hair is usually blonde or brown and this type include Scandinavians and Northern Europeans.
Type 3 skin: A darker white skin that burns in hot sun, and will see a change to skin after even short exposure to sun, tanning to a light brown. Hair colour tends to be brown, eye colour is usually brown or green and the group includes darker Caucasians.
Type 4 skin light brown skin that doesn’t easily tan, but will turn medium brown in prolonged exposure. This is the largest group and includes American Indians, Hispanics, Mediterraneans, and Asians. Hair is most often dark brown or black and eyes are brown, occasionally green.
Type 5 skin: brown skin which tans very slowly to a medium/dark brown and rarely burns. Hair is almost always dark brown or black and eyes dark brown. This group contains Hispanics, Middle Easterners , and some African Americans.
Type 6 skin: dark brown with very dark pigmentation. Eyes are dark brown and hair is usually black. There is little sensitivity to sun and sunburn is rare. This group are least prone to skin cancers and are mostly African Americans and dark-skinned Asians.
Minimal Erythemal Dose (MED)
There is a vast difference between the groups in terms of safe sun-exposure, as, clearly, group 6 have plenty of protective melanin, whereas group 1 have very little. This is important when calculating the MED, this is the amount of sunshine that will cause the skin to burn. As the natural darkness of skin increases, the MED gets longer. So, someone with Type 1 skin may expect to burn after 10 minutes, a Type 6 skin, in the same light, would remain unaffected after an hour, with roughly 7 times the protection, in terms of burning. Time in the sun is not the only factor, however and the following should be taken into account: time of the year, time of the day, altitude, latitude, ground surface and reflective surfaces.
The MED is useful in calculating how much sunshine is necessary to absorb a reasonable amount of Vitamin D for the body to remain healthy, (1,000 IU). The lighter the skin, the faster Vitamin D is absorbed. Very roughly, the Vitamin D requirement is achieved at a quarter of the MED time, so if a burn occurs after 15 minutes, only 4 minutes are necessary for adequate Vitamin D. There is some strong evidence to suggest that Vitamin D is preventative for ovarian cancers, although no definitive results have yet been published.