The mechanism of action for the photochemical properties of active ingredients in a selected sunscreen agent typically involves the absorption, reflection, or scattering of ultraviolet UV radiation. Sunscreen agents contain organic chemical and/or inorganic physical compounds that protect the skin from the harmful effects of UV radiation.Organic compounds, such as oxybenzone, avobenzone, and octinoxate, absorb UV radiation and convert it into a less harmful form of energy, such as heat. These compounds contain conjugated double bonds that allow them to absorb UV light in the UVA and/or UVB range. Upon absorption, the molecules undergo a conformational change, which leads to the release of energy in the form of heat or fluorescence.Inorganic compounds, such as zinc oxide and titanium dioxide, are physical blockers that primarily reflect and scatter UV radiation. These compounds form a protective barrier on the skin's surface, preventing UV radiation from penetrating the skin.The efficacy of a sunscreen agent is affected by various factors, including the wavelength of light and the concentration of the active ingredient:1. Wavelength of light: Sunscreen agents are designed to protect against UVA 320-400 nm and UVB 280-320 nm radiation. UVA radiation penetrates deeper into the skin and is responsible for skin aging, while UVB radiation causes sunburn and can lead to skin cancer. The efficacy of a sunscreen agent depends on its ability to absorb or reflect these specific wavelengths of light. Broad-spectrum sunscreens contain a combination of ingredients that protect against both UVA and UVB radiation.2. Concentration of the active ingredient: The concentration of the active ingredient in a sunscreen agent affects its sun protection factor SPF . Higher concentrations of the active ingredient generally provide better protection against UV radiation. However, there is a limit to the increase in protection with increasing concentration, as the relationship between concentration and SPF is not linear. For example, an SPF 30 sunscreen blocks about 97% of UVB radiation, while an SPF 50 sunscreen blocks about 98%.Other factors that can affect the efficacy of a sunscreen agent include the formulation, the presence of additional ingredients such as antioxidants and stabilizers , and the user's application technique. It is essential to apply a sufficient amount of sunscreen and reapply it regularly, especially after swimming or sweating, to ensure adequate protection against UV radiation.