Melanin is a natural pigment in our body, which is produced by melanocytes. Its concentration depends on several factors but mostly on your genes. Melanocyte concentration is equal in almost everyone but some of them make more melanin than others. So, it depends on your genes. This means, if your parents have a light shade of hair and eyes, you probably look like them.

It also gives protection against ultraviolet rays (UV) by increasing melanin concentration. But sometimes, melanin concentration increases due to many reasons like excessive sun exposure or some medical conditions. Due to more melanin concentration in your skin, your eyes may appear darker. It can be a condition called melasma, in which brown patches appear on the face. It may be due to hormones, birth control pills or excessive sun exposure.

Your skin appears dark with patches. You can cure this by consulting a dermatologist. Also, you can consider applying sunscreen regularly, wearing hats and scarves, consuming food having antioxidants (Flavonoids and Carotenoids), and avoiding over-exfoliation and scrubbing.