Re: Re: Would black hair change color after 5 months exposure to sun in a desert?

Ric,

Yes it would. However, how it does so is dependent upon many factors. 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 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 give hair its color; these are eumelanin (brown/black) and pheomelanin (yellow/red). A low concentration of eumelanin in the hair and low concentration of pheomelanin will result in an ash blond color; while more eumelanin, will result in a “dirty blond” or light brown color. Even higher eumelanin will result in deep black pigmented hair. Pheomelanin in low concentrations causes a yellow tone, increasing to strawberry red, with higher concentrations causing 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.

So yes, the hair color would change, but that change may depend on the physical and genetic makeup of the individual.

Thank you for your interesting question! What is the riddle? I’ve never heard it.
Peter

References:
http://focus.hms.harvard.edu/2006/101306/dermatology.shtml
http://www.ishrs.org/articles/hair-color.htm
Botchkareva NV, Botchkarev VA, Gilchrest BA. Fate of melanocytes during development of the hair follicle pigmentary unit. J Investig Dermatol Symp Proc. 2003 Jun;8(1): 76-9. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi? cmd=Retrieve&db=PubMed_uids=12894999&dopt=Abstract

Andrzej Slominski, Jacobo Wortsman, Przemyslaw M. Plonka, Karin U. Schallreuter, Ralf Paus, Desmond J. Tobin Hair Follicle Pigmentation J Invest Dermatol. 2005 January; 124(1): 13–21. http:// www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1201498

Ana Carolina Santos Nogueira and Ines Joekes (2004) Hair color changes and protein damage caused by ultraviolet radiation Journal of Photochemistry and Photobiology Volume 74, Issues 2-3, 27 May 2004, Pages 109-117
MadSci Anatomy Message ID Number: 1168123740.An