How Sunscreen Works to Protect the Skin from Ultraviolet Rays

Sunlight encompasses a spectrum of ultraviolet (UV) radiation, extending to visible light. The UV spectrum consists of UVA, UVB, and UVC, with wavelength ranges of 320-400 nm, 260-320 nm, and 200-260 nm, respectively. The primary function of sunlight is to fulfill the skin's vitamin D requirements and provide numerous other benefits; however, UV radiation can also have negative effects, including irritation and an increased risk of skin cancer. Protection from sunlight can be achieved physically by using UV-protective clothing, hats, and umbrellas, as well as chemically by applying sunscreen directly to the skin.

Sunscreen is a substance that can absorb at least 85% of the radiation emitted by the sun within the wavelength range of 290-320 nm, although radiation with wavelengths greater than 320 nm can still penetrate. The mechanisms of action in sunscreen can be categorized into two types: physical blocking (using ingredients such as ZnO, CaCO3, TiO2, kaolin, and MgO), which works by scattering or reflecting UV radiation to form a layer on the skin, and chemical blocking, which includes UVA filters such as benzophenone derivatives (dibenzoylmethane and oxybenzone) and UVB filters that work by absorbing UV radiation, thereby slowing the penetration process into the skin's epidermis.

In topically applied formulations, sunscreen is categorized into two mechanisms: those that reflect or scatter sunlight and those that absorb sunlight. The ability of sunscreen to block UV radiation is determined by its refractive index, particle size, dispersal state, and the thickness of the layer applied to the skin. A higher refractive index indicates a greater capacity of the sunscreen to reflect UV radiation. This type of sunscreen is commonly used as an inorganic sunscreen, making it safe for children due to its stability and low potential for allergies. Examples of active ingredients in this category include titanium dioxide (TiO2), zinc oxide (ZnO), kaolin, talc, and magnesium oxide (MgO). Kaolin, talc, and magnesium oxide can also be isolated from natural sources, as they are mineral-based.