Gradual tanning lotions contain dihydroxyacetone (DHA), a colorless sugar molecule that reacts with amino acids in the skin to produce a temporary tan. Erythrulose, another sugar, is sometimes used as an alternative to DHA due to its longer-lasting effects. The Maillard reaction, a chemical process that occurs when DHA and erythrulose interact with the skin, results in the production of brown pigments known as melanoidins. Gradual tanning lotions are applied topically and gradually develop a tan over several hours or days, providing a natural-looking glow without the harmful effects of sun exposure.