Overexposure to the sun’s harmful untraviolet (UV) radiation can cause serious health effects, including skin cancer (melanoma and non-melanoma), premature aging of the skin and skin disorders, cataracts and immune system suppression. According to the Skin Cancer Foundation, over 90% of all skin cancers are caused by overexposure to the sun. UV radiation is comprised of UV-A (320-400 nm), UV-B (290-320 nm), and UV-C (<290 nm) UV-B rays pose the greatest risk of skin cancer. The lowest UV-B dose necessary to develop a sunburn depends distinctly on the skin sensitivity of the person (i.e. skin types).

The photosensitive compositions change color irreversibly from blue to colorless when a certain dose (equal with the minimum dose to cause a sunburn) of UV-B has been received. The compositions can be part of an indicator system in the form of a patch that can be applied on skin, hats, items of clothing, swimwear or other objects (e.g. sunglasses).

The change in color of the patch will alert a user when overexposed to UV rays and compositions can be formulated for different types of skin. In addition, sunscreen can be applied on the patch surface, with the color change indicating when the sunscreen is no longer active. The problem with the sunscreen products is that users are not aware of when the sunscreen has worn off, and should be reapplied to maintain protection.

The patches can be used all year-round, as during the winter, the reflection from the snow intensifies UV radiation.