What is the primary active ingredient in most sunscreens that protects against UV radiation?

The primary active ingredient in most sunscreens that provides protection against UV radiation is zinc oxide. This substance is a physical (or mineral) sunscreen agent that works by sitting on the skin's surface, where it reflects and scatters harmful UV rays, preventing them from penetrating the skin. Zinc oxide is effective against both UVA and UVB rays, which are responsible for skin damage, including sunburn and increased risk of skin cancer.

While other ingredients may appear in sunscreens, they do not serve the primary function of UV protection. For instance, alcohol is often used in cosmetic products for its antimicrobial properties, but it does not offer UV protection. Essential oils may provide fragrance or other skin benefits, but they lack the efficacy needed for sun protection. Glycerin, a humectant, helps to keep skin moisturized but does not function as a UV blocker. Thus, zinc oxide stands out as the clear choice for UV protection in sunscreens.