Marilyn Monroe Well Known Blonde HairCredit: photo courtesy of Gentlemen Prefer Blondes trailer

Why is it that a beautiful head of long blonde hair on a five year old disappears as the child ages?  It all has to do with the genetics.  Those natural blonde locks don’t often stay that way as people age thanks to the hair color gene being “switched on.”  Not all blonde hair will darken with age, but in many cases it does.

 Brief Explanation of Genetics

 All known forms of life require three major macromolecules; proteins, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Both DNA and RNA are made of long chains of nucleotides.  RNA carries information from DNA to the sites of protein synthesis in the cell; the ribosome.  The ribosome translates or “reads” the RNA code to make a protein based on the instructions from the RNA.

 The DNA contains all of the genetic instructions used in the development and functioning of all known living organisms except RNA viruses. The segments of DNA which carry the information are called genes.  Chromosomes are long structures of DNA within cells.  As cells divide, the DNA is replicated and the chromosomes are duplicated as well, thus providing each cell a set of chromosomes.  Chromosomes are like a cookbook and genes are the recipes.  The cell has to read the gene in order to do what it is supposed to do.

 Switching on a Gene

 Genes have to be turned on or off by a specific type of protein called a transcription factor (TF).  At their simplest, TFs can either turn genes on or off.   When they turn the gene on, it is called an activator.  The TF in activator mode leads the cellular gene-reading machinery to the code.  TFs are repressors when they shut off a gene.  Basically, the TF repressors make the code invisible to the cellular gene-reading machinery.  Hair color (and eye color by the way) can darken over the years due to the respectivMaureen O’Hara with Red HairCredit: Photo courtesy of film Mcclintocke genes being turned on or off.

 The color of hair is determined by the amount of pigment melanin.  The more melanin produced in the hair follicle, the darker the color.  The genes control the amount of melanin produced according to the coding.  When the TF activates the code, more melanin is produced and the hair darkens; when it represses the code, less melanin is produced and results in lighter hair color.[2]

 It is not only blonde hair that darkens with age; red hair often darkens as well.  As people age, and the hair turns gray or white, less melanin is produced.  Geneticists continue to study what makes the TF decide to activate or repress the gene coding.  The process is more complicated, but this is a simple explanation of why hair darkens with age and then turns gray or white.


 The copyright of the article Why Does Hair Darken With Age is owned by Cheryl Weldon and permission to republish in print or online must be granted by the author in writing.

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