People with darker skin produce more eumelanin (which provides brown to black pigmentation), while those with lighter skin produce less and comparatively more pheomelanin (which gives a red to yellow pigmentation). Environmental factors like sun exposure can increase melanin production and lead to tanning or darkening of the skin.

Factors like prolonged sun exposure, hormonal changes, aging, and skin damage can disrupt melanin production, leading to dark spots, hyperpigmentation, or blotchy skin. Additionally, inflammation or irritation from acne and other skin conditions can also contribute to an uneven complexion.

These are primarily caused by an overproduction of melanin, which can be triggered by factors such as sun exposure, hormonal changes, or skin injury. 

When the skin is frequently exposed to UV rays, it produces extra melanin as a protective response, which can lead to freckles and dark spots.

UV damage from the sun can break down collagen and elastin fibers in the skin, leading to premature signs of aging like fine lines, wrinkles, and age spots. Prolonged exposure can significantly damage skin cells as well as its appearance and texture.