An evaluation of photographic methods to demonstrate the uniformity of sunscreen applied to the skin.
Sunscreen is used to help provide some protection from the harmful effects of the sun. Each sunscreen identifies its sun protection factor (SPF) which indicates the degree of protection offered by the product. However, the SPF is dependent upon an internationally agreed amount of 2 mg/cm2 being applied. Studies have shown that people rarely use sufficient sunscreen to offer protection from the sun. A simple photographic technique is described which demonstrates the uniformity of sunscreen applied by users. By employing an ultraviolet fluorescence photographic technique with a sunscreen known to exhibit fluorescent characteristics, it can be shown that in many instances sunscreen is not applied in an even layer. The SPF for the product may therefore not be achieved over the entire area of skin which was intended to be protected by the user. This photographic method could be used in a clinical setting to demonstrate application techniques of skin preparations where uniformity of product on the skin is of utmost importance.