As far back as the ancient Greeks, people have documented a funny phenomenon among pregnant women: The skin on their faces sometimes changes color. Scientists never quite knew why that happened, though they suspected that it was linked to the spike in the body’s hormones during pregnancy. Now, a new study published this week in eLife found that two sex hormones, estrogen and progesterone, play a key role in regulating the body’s synthesis of melanin, the substance that gives skin pigment.
To test the relationship between hormones and skin pigment, the researchers administered doses of the hormone estrogen to a 3D array of cells designed to mimic the structure of human skin. The longer the cells were exposed to estrogen, the more melanin they produced; after four days, the cells produced up to 300 percent more melanin than before they were exposed to estrogen. The researchers did the same test with progesterone (a synthetic version, progestin, is in oral contraceptives), which the body also produces during pregnancy, and found that cells decreased their melanin production when exposed to that hormone.
That was intriguing, since the melanocytes (the cells that produce melanin) don’t have traditional hormone receptors.
When the researchers took a closer look at the molecular pathways, they discovered that the hormones activate special pathways in the melanocyte cell membranes that tell the cell to create more or less melanin. To test their hypothesis, the researchers eliminated those receptors from the cells and found that the hormones no longer changed how much melanin they produced, as they predicted.
This discovery could lead to treatments for skin pigment conditions such as vitiligo, in which skin loses pigment because melanocytes are destroyed. It could also help researchers develop non-toxic ways to alter skin tone for cosmetic purposes, like making a person look tan without exposure to UV rays or paler without using damaging bleach on the skin.
In fact, the researchers isolated one of the melanin-increasing compounds and applied it as cream to the inside of mice’s ears for three weeks, which visibly darkened their skin. What’s not yet clear is if these sorts of creams would have any side effects—for example, on fertility—if used on humans.
In future studies the researchers hope to investigate more pathways through which hormones can affect cells’ melanin production, according to a press release.