Have you ever noticed that freckles become more frequent when it’s warm outside, or that the older you get, the more often small brown spots start to appear on your skin?   This happens because, in the epidermis, or top layer of skin, there are small cells called melanocytes that produce the complex polymer responsible for skin pigment called melanin. Although every person has the same number of melanocytes, the amount of melanin they produce is up to the instructions found within each...