Freckles are small brown spots on the skin caused primarily by an overproduction of melanin, the pigment responsible for skin and hair color, triggered by exposure to ultraviolet (UV) radiation from the sun

. When skin is exposed to UV-B radiation, melanocytes (the cells that produce melanin) increase melanin production, causing freckles to become darker and more visible

. Genetics also play a significant role in the development of freckles. Variants of the MC1R gene influence the type of melanin produced—pheomelanin or eumelanin. People who produce more pheomelanin tend to have lighter skin, red or blonde hair, and are more prone to freckles because pheomelanin offers less protection against UV radiation. Conversely, eumelanin provides better protection and is more common in individuals with darker skin and hair, who are less likely to freckle

. Freckles typically appear on sun-exposed areas such as the face, arms, neck, and chest, and they often become more pronounced with increased sun exposure, especially during summer months. People with lighter skin tones and certain genetic backgrounds are more susceptible to developing freckles

. In summary, freckles are caused by a combination of genetic predisposition and sun exposure, which stimulates melanin production in the skin