Sunscreens and UVA protection: a major issue of minor importance.

The ultraviolet A (320-400 nm) (UVA) exposure of sunscreen-protected skin depends not just on the absorption characteristics of the product but also on a number of other factors. These include the amount of sunscreen applied and how it is spread over the skin. The importance of the spectral absorption of a sunscreen compared with these other two variables in controlling cutaneous UVA exposure is examined here using an analysis of variance approach. The results demonstrate that by far the most important factor is the application of a liberal quantity of sunscreen. Less important is to spread it uniformly, and least important is the precise shape of the sunscreen-absorption spectrum, providing, of course, the spectrum extends into the UVA region.