Skip over navigation to text  The Library of Congress >> Researchers >> Science Reference Services  
Everyday Mysteries: Fun Science Facts from the Library of Congress  
<< HOME           << See More Everyday Mysteries>>       << Ask a Question >>   
Find in
 
Question:

    Why does hair turn gray?

Answer:    

    It is well known that gray hair results from a reduction of pigment, while white hair has no pigment, but why this happens remains somewhat of a mystery.

Parents often cite having teenagers as the cause of gray hair. This is a good hypothesis, but scientists continue to investigate why hair turns gray. In time, everyone’s hair turns gray. Your chance of going gray increases 10-20% every decade after 30 years.

Initially, hair is white. It gets its natural color from a type of pigment called melanin. The formation of melanin begins before birth. The natural color of our hair depends upon the distribution, type and amount of melanin in the middle layer of the hair shaft or cortex.

Hair has only two types of pigments: dark (eumelanin) and light (phaeomelanin). They blend together to make up the wide range of hair colors.

Melanin is made up of specialized pigment cells called melanocytes. They position themselves at the openings on the skin’s surface through which hair grows (follicles). Each hair grows from a single follicle.

The process of hair growth has three phases:

  • Anagen: This is the active growth stage of the hair fiber and can last from 2- 7 years. At any given moment 80-85% of our hair is in the anagen phase.

  • Catagen: Sometimes referred to as the transitional phase, which is when hair growth begins to “shut down” and stop activity. It generally lasts 10- 20 days.

  • Telogen: This occurs when hair growth is completely at rest and the hair fiber falls out. At any given time, 10-15 % of our hair is in the telogen phase, which generally lasts 100 days for scalp hair. After the telogen phase, the hair growth process starts over again to the anagen phase.

As the hair is being formed, melanocytes inject pigment (melanin) into cells containing keratin. Keratin is the protein that makes up our hair, skin, and nails. Throughout the years, melanocyctes continue to inject pigment into the hair’s keratin, giving it a colorful hue.

With age comes a reduction of melanin. The hair turns gray and eventually white.

So why does our hair turn gray or white?

Dr. Desmond Tobin, professor of cell biology from the University of Bradford in England, suggests that the hair follicle has a “melanogentic clock” which slows down or stops melanocyte activity, thus decreasing the pigment our hair receives. This occurs just before the hair is preparing to fall out or shed, so the roots always look pale.

Moreover, Dr. Tobin suggests that hair turns gray because of age and genetics, in that genes regulate the exhaustion of the pigmentary potential of each individual hair follicle. This occurs at different rates in different hair follicles. For some people it occurs rapidly, while in others it occurs slowly over several decades.

In a February 2005 Science article (Nishimura, et al.) Harvard scientists proposed that a failure of melanocyte stem cells (MSC) to maintain the production of melanocytes could cause the graying of hair. This failure of MSC maintenance may result in the breakdown of signals that produce hair color.

There are other factors that can change the pigmentation of hair, making it lighter or darker. Scientists have divided them by intrinsic (internal) and extrinsic (external) factors:

Intrinsic factors:

  • Genetic defects
  • Hormones
  • Body distribution
  • Age

Extrinsic factors:

  • Climate
  • Pollutants
  • Toxins
  • Chemical exposure

In 2009, scientists in Europe described how hair follicles produce small amounts of hydrogen peroxide. This chemical builds on the hair shafts, which can lead to a gradual loss of hair color. (Wood, J.M et al. Senile hair graying: H2O2 mediated oxidative stress affect human hair color by blunting methionine sulfoxide repair. FASEB Journal, v. 23, July 2009: 2065-2075).

Hair-raising facts:

  • An average scalp has 100,000-150,000 hairs.

  • Hair is so strong that each hair can withstand the strain of 100 grams (3.5 ounces). An average head of hair could hold 10-15 tons if only the scalp was strong enough!

  • Human hair grows autonomously, that is each hair is on its own individual cycle. If all our hair were on the same cycle, we would molt!

  • Hair has the highest rate of mitosis (cell division). An average hair grows 0.3 mm a day and 1 cm per month.
Standard DisclaimerRelated Web Sites

Library of Congress Web SiteFurther Reading
  • Brallier, Jess M. Hairy science. New York, Planet Dexter, c2000. (Juvenile)
    (Science fair projects involving hair)
  • Morioka, Kiyokazu. Hair follicle: differentiation under electron microscope: an atlas. Tokyo, New York, Springer, c2005. 150 p.
  • Nishimura, Emi K., Scott R. Granter, and David E. Fisher. Mechanisms of hair graying: incomplete melanocyte stem cell maintenance in the niche. Science, v. 307, Feb. 4, 2005: 720-723.
  • Robbins, Clarence R. Chemical and physical behavior of human hair. New York, Springer, c2002. 483 p.
  • The Science of hair care. Edited by Claude Bouillon and John Wilinson. Boca Raton, Taylor & Francis, 2005. 727 p.
  • Steingrimsson, Eirikur, Neal G. Copeland, and Nancy A. Jenkins. Melanocyte stem cell maintenance and hair graying. Cell, v. 121, April 8, 2005: 9-12.
  • Tobin, Desmond J. and R. Paus. Graying: gerontobiology of hair follicle pigmentary unit. Experimental gerontology, v. 36, 2001: 29-54.
  • Tobin, Desmond J. Biology of hair pigmentation. In Skin, hair, nails: structure and function. Edited by Bo Forslind, Magnus Lindberg, and Lars Norlen. New York, Basel, Switzerland, Marcel Dekker, c 2004: 319-363.

SearchFor more print resources...
Search on "hair" and "Hair care and hygiene" in the Library of Congress Online Catalog.

Drawing of young hair follicle.
From MedlinePLus Encyclopedia, NIH


Drawing of old hair follicle.
From MedlinePLus Encyclopedia, NIH

 

Drawing of melanin and  melanocyte.
From MedlinePLus Encyclopedia, NIH


Victorian era ad with  women in hoop skirts standing  beneath  gothic style arches.
Circassian Hair Dye. From the Prints &
Photographs Division, Library of Congress.


Victorian era ad - color painting with lady seated at mirror and woman combing her long hair.
Kendall's amboline for the hair. From the
Prints and Photographs Division, Library of Congress.


Photo of a woman in a long dress with  long hair down to her knees.
From Prints and Photographs
Division, Library of Congress.


Ad for Mary T. Goldman's Gray Hair Color Restorer, with  woman with half black hair, half gray hair.
Photo courtesy of the National
Library of Medicine.

Top of page

Top of Page

 
<< HOME           << See More Everyday Mysteries>>       << Ask a Question >>
   
 The Library of Congress >> Researchers >> Science Reference Services
  September 27, 2013
Legal | External Link Disclaimer
Contact Us