MadSci Network: Anatomy |
Mayra, What you report is what we experience here with patients who spend months (notice the plural) in more tropical climates and return to the Northeast USA. You are not imagining the deepening of hair color darkness in response to lengthened light stimulus. It is quite real, especially if you are of olive or darker skin complexion. Perhaps a refresher note on melanocyte and hair pigmentation would be appropriate. For brevity, we will leave out graying of hair. Melanocytes do not color hair as it is originally formed. Fresh hair, under the skin has no color, it picks up color as it lengthens. The hair is going to grow no matter if the hair is colored or not. The hair shaft develops in the follicle, surrounded by melanocytes. The melanocyte pigments enter the hair shaft cortex by diffusion through the cuticle and keratin. So the important fact is that the melanocytes act independently of the growth of hair. Melanocytes simply behave as melanocytes and the pigment is “picked up” adventitiously by the growing hair. There are two types of pigment that gives hair its color, eumelanin (brown/black), and pheomelanin(yellow/red). A low concentration of eumelanin in the hair and low concentration of pheomelanin will result in ash blond color, more eumelanin, “dirty blond” or light brown color. Higher eumelanin will result in deep black pigmented hair. Pheomelanin in low concentrations causes a yellow tone, increasing to strawberry red to higher concentrations causeing increasing red color effects. Pheo- and eu- melanins usually occur paired and create the many varied effects we see, such as auburn hair. Pheomelanin breaks down more slowly than eumelanin when oxidized, which accounts for darker hair turning red to orange to yellow during the bleaching process. That is also the reason why mummies all have red hair. Color producing melanocytes are not sensitive to light stimulus, per se. However, keratinocytes are very sensitive to light. When exposed to sunlight, keratinocytes release melanocyte-stimulating hormone (MSH), which binds to the melanocyte activating receptor, Mc1r on the melanocyte. Thus the melanocytes are activated and produce pigment. Melanocytes increase their production of pheo- and eu- melanins, as programmed by the genetic make up of the individual. For your first Question: If one changes geography to a climate of longer day time, assuming they spend a long enough time there to notice, ie: greater than 6 months, will experience increased hair follicle melanocyte production of the respective melanins. That will be noticed by pronounced hair color change. Whether that is a deepening or an apparent bleaching of color is dependent on the melanins produced by melanocytes that are responding to MSH. MSH, light time and your genetics are the cumulation of your hair color deepening while in Brazil. Enjoy! Thank you for this very interesting question! On your second question: I have asked a number of my collegues. We are a bit stymied by your second question and are most curious. We collectively can not think of a rationale or reference to this phenomenon. Sorry. Perhaps you should re-post it to the moderator in an effort to locate an adequate answer. Thank you very much! Peter Ref: http://fo cus.hms.harvard.edu/2006/101306/dermatology.shtml http://www.ishrs.org/articles/hair-color.htm http://www.ncbi.nlm.n ih.gov/entrez/query.fcgi? cmd=Retrieve&db=PubMed&list_uids=12894999&dopt=Abstract http://www.pubmedcentral.nih.gov/articlerender.fcgi? artid=1201498
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