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. Zinc oxide (also known as Zinc Gelatin, ZnO, CI 77947; Nogenol; Pigment white 4) is used in concentrations of up to 25%. Its job is to physically block UVB and some UVA rays, as opposed to filter them. It’s stable in sunlight, and is not known to cause irritation in skin. It’s an ideal addition to broad spectrum sunscreens and is approved in both the US and Canada. 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.