The main purpose of sunscreen is to protect the skin from the harmful effects of ultraviolet (UV) radiation emitted by the sun. Sunscreens work by either absorbing, reflecting, or scattering UV rays, thus preventing them from penetrating the skin and causing sunburn, skin damage, and increasing the risk of skin cancer. Proper and regular application of sunscreen is essential for maintaining skin health, especially during prolonged sun exposure. It's recommended to choose a broad-spectrum sunscreen with an appropriate SPF level, reapply every two hours, and use additional sun protection measures like wearing hats and seeking shade.