Sunscreen agents, also known as ultraviolet UV filters, protect the skin from harmful UV radiation by employing a combination of physical and chemical mechanisms. UV radiation is divided into three types based on wavelength: UVA 320-400 nm , UVB 280-320 nm , and UVC 100-280 nm . Sunscreen agents primarily protect against UVA and UVB radiation, as UVC is mostly absorbed by the Earth's atmosphere.The mechanism of action for sunscreen agents can be categorized into two types: physical inorganic and chemical organic protection.1. Physical inorganic sunscreen agents:Physical sunscreen agents, such as titanium dioxide TiO2 and zinc oxide ZnO , are inorganic compounds that act as a physical barrier on the skin's surface. They protect the skin by reflecting, scattering, and absorbing UV radiation. These agents are often referred to as "mineral sunscreens" or "physical blockers."The mechanism of action for physical sunscreen agents involves:a. Reflection: The inorganic particles in physical sunscreens reflect a portion of the incident UV radiation, preventing it from penetrating the skin.b. Scattering: The particles also scatter UV radiation, causing it to change direction and reducing the amount of radiation that reaches the skin.c. Absorption: Physical sunscreen agents can also absorb some UV radiation, converting it into a less harmful form of energy, such as heat.2. Chemical organic sunscreen agents:Chemical sunscreen agents, such as avobenzone, oxybenzone, and octinoxate, are organic compounds that absorb UV radiation and convert it into a less harmful form of energy. These agents are often referred to as "chemical absorbers" or "organic filters."The mechanism of action for chemical sunscreen agents involves:a. Absorption: When UV radiation strikes the skin, the chemical sunscreen agents absorb the energy and undergo a temporary molecular transformation, known as an excited state.b. Energy dissipation: The excited molecules then release the absorbed energy in the form of heat or by emitting lower-energy, longer-wavelength radiation such as visible light or infrared radiation , returning to their original molecular structure.c. Photostability: A good chemical sunscreen agent should be photostable, meaning it can undergo multiple absorption-dissipation cycles without breaking down or losing its protective capabilities.In summary, sunscreen agents protect the skin from UV radiation through a combination of physical and chemical mechanisms, including reflection, scattering, and absorption of UV radiation, as well as the dissipation of absorbed energy in the form of heat or lower-energy radiation. By reducing the amount of harmful UV radiation that penetrates the skin, sunscreen agents help prevent sunburn, premature aging, and skin cancer.