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. Octinoxate is the most commonly used UVB blocking ingredient in sunscreens. It does not filter UVA rays. When octinoxate is exposed to sunlight, it loses its effectiveness, which is a glaring limitation considering that its purpose is to protect the skin from sunlight. That is why it is usually combined with other sunscreen ingredients. An odd combination, though, is when octinoxate is combined with avobenzone, it degrades even faster. Octinoxate is easily absorbed into the skin, which can be toxic because it produces estrogen-like effects. However, there is little agreement on what concentration is toxic. The maximum recommended by the FDA is 7.5%. Bottom line: More research is needed. Given that it isn’t even very stable in sunlight, sunscreens that don’t contain octinoxate might be a better choice. 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.