What stimulates the production of melanin in skin cells?

Melanin production in skin cells is primarily stimulated by exposure to ultraviolet (UV) radiation from sunlight. When the skin is exposed to UV rays, melanocytes, which are specialized cells in the skin, respond by increasing the production of melanin. This process serves as a natural defense mechanism to protect the skin from potential damage caused by UV light. Increased melanin results in a darker pigmentation, which aids in absorbing some of the harmful rays and reducing the risk of skin damage.

While artificial light can also have some effects on skin, it typically does not emit UV radiation to the same extent as natural sunlight, making it a less effective stimulus for melanin production. Other factors like humidity and temperature do not have a direct role in stimulating melanin synthesis; rather, they may influence skin condition or comfort but do not provoke the same biological response as UV exposure. Thus, the natural and primary stimulus for melanin production remains sunlight.