What is the primary cause of variations in individual skin tone?

The primary cause of variations in individual skin tone is melanin production. Melanin is the pigment produced by melanocytes in the skin, and it plays a crucial role in determining the color of the skin. Different individuals have varying levels of melanin, which can be influenced by genetic factors. Higher concentrations of melanin lead to darker skin tones, while lower levels result in lighter skin tones. This variance provides protection against harmful effects of UV radiation and is an important factor in evolutionary adaptation.

While sun exposure can affect skin tone temporarily by increasing melanin production in response to UV radiation, it does not fundamentally change an individual's base skin tone, which is determined primarily by genetic factors. Skin thickness and hydration levels can influence the appearance of the skin and its overall health but do not directly affect the biological pigment composition responsible for skin color. Thus, melanin production is indeed the foundational reason for the differences in skin tone among individuals.