How does melanin function in the skin?

Melanin plays a crucial role in the skin by providing pigmentation, which is responsible for the color of the skin, hair, and eyes. Additionally, one of its key functions is to protect the skin against the harmful effects of ultraviolet (UV) radiation from the sun. When the skin is exposed to UV light, melanin production increases, resulting in a tan that serves as a natural defense mechanism. This helps to absorb and dissipate UV radiation, reducing the risk of DNA damage that could lead to skin cancers.

The other choices do not accurately represent the primary functions of melanin. While melanin does influence hair color, its main role is not the direct darkening of hair. Hydration of the skin is primarily maintained by lipids and moisture factors, whereas melanin itself doesn't provide hydration. Lastly, although sunlight does aid in the production of vitamin D in the skin, the role of melanin does not include vitamin D synthesis. Instead, melanin is more concerned with protecting the skin from the sun's harmful rays. Therefore, the correct understanding of melanin's function emphasizes its protective properties against UV radiation while providing pigmentation.