Water resistance and extended wear sunscreens.

The effectiveness of a sunscreen product can be reduced by sweating, friction, water immersion, or any other force that has the potential to remove the product from the surface of the skin. Substantivity (resistance to removal by water or sweat) along with durability (resistance to removal by wear) during physical activity are important aspects of sunscreen performance along with the fundamental protection provided against sunburn and ultraviolet-induced skin damage. Standards for measuring substantivity and other performance characteristics are available in regulations or guidelines around the world, but these regulations vary concerning the labeling and communication of product performance to consumers. Sunscreens alone should not be relied on to prevent all of the possible harmful effects of sun exposure. Variation between individuals, the substantivity and durability of products, and exposure conditions all play a role in the performance of sunscreens.