Sunscreen agents protect the skin from harmful ultraviolet UV radiation by employing a combination of physical and chemical mechanisms. The two primary types of UV radiation that reach the Earth's surface are UVA 320-400 nm and UVB 280-320 nm . UVA penetrates deeper into the skin and contributes to skin aging and DNA damage, while UVB causes sunburns and is the primary cause of skin cancer. Sunscreen agents can be classified into two main categories: physical inorganic and chemical organic sunscreens.1. Physical inorganic sunscreens: These sunscreens contain mineral-based ingredients such as zinc oxide and titanium dioxide. They act as physical barriers that protect the skin by reflecting and scattering UV radiation. Physical sunscreens are effective against both UVA and UVB radiation. They form a protective layer on the skin's surface, preventing UV radiation from penetrating the skin. Physical sunscreens are less likely to cause skin irritation and are often used in sunscreens for sensitive skin or children.Mechanism of action: Physical sunscreens work by reflecting and scattering UV radiation. When UV radiation hits the sunscreen particles, the particles bounce the radiation back, preventing it from reaching the skin. This is a physical process that does not involve any chemical reactions.2. Chemical organic sunscreens: These sunscreens contain organic compounds that absorb UV radiation and convert it into a less harmful form of energy, such as heat. Common chemical sunscreen ingredients include avobenzone, oxybenzone, octinoxate, and octisalate. Chemical sunscreens are often formulated to provide broad-spectrum protection, meaning they protect against both UVA and UVB radiation.Mechanism of action: Chemical sunscreens work by absorbing UV radiation. When UV radiation hits the sunscreen molecules, the molecules absorb the energy and undergo a chemical reaction that transforms the energy into a less harmful form, such as heat. This process is called "photochemical quenching." The sunscreen molecules then return to their original state, ready to absorb more UV radiation. This cycle continues until the sunscreen molecules are depleted or washed away.In summary, physical sunscreens protect the skin by reflecting and scattering UV radiation, while chemical sunscreens protect the skin by absorbing UV radiation and converting it into a less harmful form of energy. Both types of sunscreens play a crucial role in preventing skin damage, premature aging, and skin cancer caused by exposure to harmful UV radiation. The choice between physical and chemical sunscreens depends on individual preferences, skin type, and specific needs.