The mechanism of photoprotection by UVB/UVA filters in commercial sunscreen formulations involves the absorption, reflection, or scattering of ultraviolet UV radiation, preventing it from penetrating the skin and causing damage. There are two main types of filters used in sunscreens: organic chemical filters and inorganic physical filters.1. Organic filters: These filters consist of molecules that absorb UV radiation and convert it into a less harmful form of energy, such as heat. They are designed to absorb specific wavelengths of UV radiation, with some filters targeting UVB rays 290-320 nm and others targeting UVA rays 320-400 nm . Examples of organic filters include oxybenzone, avobenzone, octinoxate, and octocrylene.2. Inorganic filters: These filters, also known as physical or mineral filters, consist of small particles of minerals such as zinc oxide or titanium dioxide. They work by reflecting or scattering UV radiation, preventing it from reaching the skin. Inorganic filters provide broad-spectrum protection, meaning they protect against both UVA and UVB rays.To improve the photostability of UV filters and ensure greater protection against harmful UV rays, several strategies can be employed:1. Combination of filters: Using a combination of different UV filters with complementary absorption spectra can provide broader protection and improve photostability. This is because the filters can work together to absorb, reflect, or scatter a wider range of UV wavelengths.2. Photostabilizers: Adding photostabilizers, such as antioxidants or other stabilizing agents, can help to prevent the degradation of UV filters when exposed to sunlight. This can prolong the effectiveness of the sunscreen and provide better protection.3. Encapsulation: Encapsulating UV filters in micro- or nano-sized particles can help to protect them from photodegradation and improve their stability. This can also improve the distribution of the filters on the skin, providing more even protection.4. Formulation optimization: Optimizing the formulation of the sunscreen, such as the use of emollients, emulsifiers, and other ingredients, can help to improve the stability and performance of the UV filters. This can also enhance the feel and spreadability of the sunscreen, making it more user-friendly.5. Use of inorganic filters: As inorganic filters like zinc oxide and titanium dioxide are inherently more photostable than some organic filters, using them in sunscreen formulations can provide more stable and long-lasting protection.By employing these strategies, the photostability of UV filters in commercial sunscreen formulations can be improved, ensuring greater protection against harmful UV rays and reducing the risk of skin damage, premature aging, and skin cancer.