Freckles are an esthetic controversy. People who have lots of them usually wish they didn't. And those who don't have them are intrigued by them, perhaps wishing for some of their own. Something everyone can agree upon; however, is that freckles contain a high amount of melanin.
Produced by melanocytes, which are specialized cells, melanin is the protein responsible for pigment in skin, eyes and hair. Melanin in skin is produced in response to sunlight, darkening the skin to create a protective layer and block harmful UV rays. While melanin typically is produced evenly across skin, freckles occur when it develops in clumps.
Freckles are similar to lentigines, also known as liver spots; although lentigines are formed due to a higher concentration of melanocytes in given areas of skin, rather than the clumping of melanin.
These melanocytes still produce melanin but unlike melanin, melanocytes remain at the same skin site, produce permanent dark spots on skin.
A Clue Behind the Spots
While scientists understand how freckles are formed, they are unsure of the reason melanin is distributed unevenly in some individuals. As a SciShow episode explained, freckles are caused by MC1R, a gene that instructs certain cells to make melanin. MC1R decides how much of two melanin types a person will have in skin, hair and eyes:
1. Eumelanin, which produces darker brown skin and hair tones, and
2. Pheomelanin, which produces reddish yellow skin and hair tones.
"If your MC1R gene is working as it should, your body will produce more eumelanin, which results in darker hair and skin," explained Sarah Emerson at Motherboard. "However, if that gene is malfunctioning, you’ll produce more pheomelanin, making you more likely to have fairer skin, red or blonde hair and freckles."
However, obviously not all red-haired people have freckles, and not all freckled people have red hair even though the two are believed to be controlled by the same MC1R gene.
This means other factors are at play; for one, red hair is a recessive trait and freckles are a dominant trait. Looks like science has more dots to connect in this area.