Understanding the active ingredients in sunscreen is a bit like learning a foreign language that uses a different alphabet. Suffice it to say in short that sunscreens are made up of a combination of two types of ingredients: those that reflect ultraviolet (UV) rays and those that absorb UV rays. Although that might sound simple enough, there are also two types of rays: UVA rays and UVB rays. UVB causes sunburn at the outer layers of skin, but UVA causes sun damage that reach deeper layers of skin. Both UVA and UVB radiation can contribute to the development of skin cancer. Sulisobenzone (also known by Benzophenone-4; BP4; Uvinul MS40; Escalol 577) is approved by the FDA in concentrations of 5% and in Canada is approved by Health Canada at 6% concentrations. It works to filter out both UVA and UVB rays. It’s an excellent addition to broad spectrum sunscreens. Keep in mind that a sunscreen’s Sun Protection Factor (SPF) is a gauge of how well the formula protects the skin from UVB rays. It does not gauge protection from UVA rays.