The conditions under which most outdoor sports are practiced alter the effectiveness of a sunscreen to protect the skin. Under these sports conditions, certain factors become more relevant than when under non-active conditions. When lying on a beach towel next to the water you may only require an SPF15 sunscreen to see you safely through an afternoon of sun exposure.
However, when practicing sport your environment changes dramatically, as do the elements you are exposed to. So on the same afternoon that you can safely sunbathe with SPF15, an SPF30 or 45 might well be required for sufficient sun protection while you are practicing sport. The extent to which a sunscreen is both waterproof and sweatproof to ensure lasting protection during sport therefore becomes extremely important.
Water greatly affects the sun’s UV intensity, so it is especially important to apply a quality sunscreen for water sports. Not only does water have the tendency to wash sunscreen from your skin to leave you unprotected, water droplets on the skin also magnify the sun’s rays and increase their intensity. Reflection from the water surface greatly increases the UV intensity, while under water the UVA to UVB ratio is altered so that UVA becomes much stronger.
Sweat is a natural part of all sport. Not only does sweating remove moisture from the skin, it can also remove sunscreen leaving you unprotected. Sweat droplets on the skin also act to magnify the intensity of the sun’s UV radiation.