Melanin, in people with naturally pigmented skins, offers a high level of photoprotection against the adverse molecular and clinical effects of solar ultraviolet radiation but, in contrast, has a modest inhibitory effect on vitamin D synthesis. Tanning in those with light skin offers relatively modest photoprotection. Sunscreens have the potential to offer high levels of protection in people who lack melanin. In theory, sunscreens can give protection comparable with that of deeply pigmented skin. This depends on the labeled sun protection factor (SPF) which in turn depends on how well the sunscreen is applied. In most cases, this will not achieve the desired SPF. The threshold dose for vitamin D synthesis is much lower than that for sunburn, such that vitamin D synthesis is still possible with sunscreen application.