MadSci Network: Anatomy |
Your question is good. I'm not certain of the answer, but I think there is a distinction to be made between freckles, which come and go based on sun exposure, and moles, which are basically darker, permanent skin marks (also called beauty marks). Both are dark due to the production of the pigment melanin, which as you said is made by melanocytes. There are melanocytes spread evenly throughout your skin, which give you your background skin color. In some spots (moles) there is a bunch of melanocytes together, which continuously are making melanin, giving you the mole. For the case of freckles, melanocytes in a little area started temporarily making more melanin due to sun exposure, but stop when the sun exposure stops (i.e. in the winter). The melanin then fades away from the freckles as the skin cells naturally turnover and get replaced by new ones, leaving you without a freckle in this spot (until next summer!). Moles have the potential for changing over the course of one's lifetime. Often the change is not dangerous, but sometimes the mole changes into a cancer called melanoma. The chance of melanoma increases if you spend lots of time in strong sun without any sunscreen. If a mole changes in shape, color, or becomes raised, you should see a doctor about whether it may need removal. Hope this helps, BRIAN E.
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