When exposed to much sunshine, our skin darkens. This is due to the skin pigment that is known as:

Melanin

The correct answer is Option (4) – Melanin

To protect itself from the damaging effects of the sun, your skin increases its production of the brown pigment called melanin.

The extra melanin makes your skin look darker or sun-tanned.

Sometimes the sun causes an uneven increase in melanin production, which produces irregular coloring (pigmentation) of the skin.