Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotective topical product for the skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, foams (such as an expanded foam lotion or whipped lotion), sticks, powders and other topical products. Sunscreens are common supplements to clothing, particularly sunglasses, sunhats and special sun protective clothing, and other forms of photoprotection (such as umbrellas). Sunscreen is on the World Health Organization's List of Essential Medicines.

Sunscreen products may be classified according to the type of active ingredient(s) present in the formulation (inorganic compounds or organic molecules) as:

Medical organizations such as the American Cancer Society recommend the use of sunscreen because it aids in the prevention of squamous cell carcinomas. The routine use of sunscreens may also reduce the risk of melanoma. To effectively protect against all the potential damages of UV light, the use of broad-spectrum sunscreens (covering both UVA and UVB radiation) has been recommended.

Early civilizations used a variety of plant products to help protect the skin from sun damage. For example, ancient Greeks used olive oil for this purpose, and ancient Egyptians used extracts of rice, jasmine, and lupine plants whose products are still used in skin care today. Zinc oxide paste has also been popular for skin protection for thousands of years. Among the nomadic sea-going Sama-Bajau people of the Philippines, Malaysia, and Indonesia, a common type of sun protection is a paste called borak or burak, which was made from water weeds, rice, and spices; it is used most commonly by women to protect the face and exposed skin areas from the harsh tropical sun at sea. In Myanmar, thanaka, a yellow-white cosmetic paste made of ground bark, is traditionally used for sun protection. In Madagascar, a ground wood paste called masonjoany has been worn for sun protection, as well as decoration and insect repellent, since the 18th century, and is ubiquitous in the Northwest coastal regions of the island to this day.

In 1820, Sir Everard Home, an English physician, conducted observational experiences that suggested there is something other than heat from the sun that causes sunburns. He also documented the protective effect of having dark skin on sun burns. The link between UV rays and skin burns was established experimentally by Erik Johan Widmark in 1889, which initiated research into substances capable of blocking or absorbing UV radiation for skin protection. The first commercial sunscreen was under the names Zeozon for sunburn prophylaxis and Ultrazeozon against glacier burn from Kopp & Joseph produced with aesculin derivatives. Once Wilhelm Hausser and Wilhelm Vahle had determined the wavelength responsible for sunburn on the skin at 297 nm, all that remained was to find substances that absorb in this specific wavelength range. It was Emil Klarfeld who identified two substances Salicylicacidbenzylester and Benzylcinnamic acid ester that absorb in the requested range. He formulated a product with these two ingredients and the company Lehn & Fink launched the product under the Dorothy Gray brand. Followed by the first sunscreen, invented in Australia by chemist H.A. Milton Blake, in 1932 formulating with the UV filter Tannic acid at a concentration of 10%. Its protection was verified by the University of Adelaide. Research into new products continued unabated in the 1930s. In Germany, the physicist Erich Merkel (1886-1974) and his colleague Christian Wiegand (1901-1978), a chemist, wanted to find out whether it was possible to form pigment on human skin through solar radiation without sunburn. They thought that a substance that absorbs between 320 nm and 290 nm should prevent the skin from reddening but allow the tanning rays to pass through. Merkel and Wiegand worked at IG Farben in the physics laboratory in Elberfeld. Merkel tested the first filter substances identified by Wiegand in practice. He climbed Corvatsch and the Jungfraujoch to do this. The experiments were encouraging. Now the researchers tested their further developments on female employees in the laboratory. They stuck jars of the substances on their backs, forearms, or thighs and measured the effect; novantisolic acid turned out to be the best candidate. The substance was patented as a sunscreen protection agent in Germany in 1933 and a year later in the United States. IG Farben founded a subsidiary, Drugofa, with the aim of launching a product with the active ingredient on the market under the name Delial. In 1936, L'Oreal released its first sunscreen product, formulated by French chemist Eugène Schueller.

The US military was an early adopter of sunscreen. In 1944, as the hazards of sun overexposure became apparent to soldiers stationed in the Pacific tropics at the height of World War II, Benjamin Green, an airman and later a pharmacist, produced Red Vet Pet (for Red Veterinary Petrolatum) for the US military. Sales boomed when Coppertone improved and commercialized the substance under the Coppertone girl and Bain de Soleil branding in the early 1950s. In 1946, Austrian chemist Franz Greiter introduced a product, called Gletscher Crème (Glacier Cream), subsequently became the basis for the company Piz Buin, named in honor of the mountain where Greiter allegedly received the sunburn.

In 1974, Greiter adapted earlier calculations from Friedrich Ellinger and Rudolf Schulze and introduced the "sun protection factor" (SPF), which has become the global standard for measuring UVB protection. It has been estimated that Gletscher Crème had an SPF of 2.

Water-resistant sunscreens were introduced in 1977, and recent development efforts have focused on overcoming later concerns by making sunscreen protection both longer-lasting and broader-spectrum (protection from both UVA & UVB rays), more environmentally friendly, more appealing to use, and addressing the safety concerns of petrochemical sunscreens (i.e., FDA studies showing their systematic absorption into the bloodstream).