What is the reason behind greying of hair with age?
SAPNA PRASAD, Chennai
The reason for hair greying is that it is either due to intrinsic factors such as genetic defects, hormones, age etc or extrinsic factors such as climate, pollutants, toxins, chemical exposure etc. Hair greying is a physiological process and is not always related to one’s age as grey hair can occur in teens and range into late 50’s and even older. Premature hair greying is basically hereditary and inherited from parents or grandparents.
Hair follicle is composed of specialized group of cells called melanocytes and keratinocytes and undergoes a cyclic process of degeneration and regeneration regulated by endocrine and paracrine mediators. Melanocytes are responsible for the melanotic pigment production and for the delivery of melanin to the keratinocytes of the hair follicle. Keratinocytes produce keratin, the chief protein in hair.
The natural colour of hair depends upon the amount and type of melanin pigments. Made from two aminoacids such as tyrosine and phenylalanine, melanin pigments are produced by melanocytes by a process called melanogenesis. There are two types of melanin : eumelanin, which is dark brown or black, and pheomelanin, which is reddish yellow. They blend together to form a wide range of hair colours and pass the melanin to the keratin – producing cells called keratinocytes.
This process employs the enzymes such as tyrosinase, tyrosinase-related protein 1, and tyrosinase –related protein 2, and takes place inside of organelles called melanosomes. Melanin production has been shown to occur only during the anagen phase ( a period of growth ) of the follicular cycle.
When the keratinocytes die, they retain the melanin. When failure of melanocyte stem cells (MSC) to maintain production of melanocytes occur or melanocytes die, then the hair turns grey. With age melanocytes lose their ability to make pigment then the colour is absent from new hair. The control of this pigment production is complex but there are genetic factors. One factor is MCIR gene and alleles of this gene are associated with red hair in humans. Thus hair follicle has a ‘melanogentic clock’ which slows down or stops melanocyte activity, thus decreasing the pigment our hair receives.
Due to the presence of superoxide dismutase ( SOD ) enzyme each of hair cells produce a tiny bit of hydrogen peroxide on their own. As we get older and due to reduction of the enzyme catalase, these tiny bits becomes a big bits and begin to damage hair follicles and block the melanin production.
So, hair bleaches itself from within and the pigmentation becomes grey, then to white. In younger people catalase breaks the hydrogen peroxide down into water and oxygen and removes it from the body. As we age, we lose some of this enzyme and buildup of hydrogen peroxide occur. Stress causes the release of numerous neurotransmitters in our fight or flight response and long term production of this can cause DNA damage and promote aging and greying of hair.
DR. SAINUDEEN PATTAZHY
Kollam, Kerala
COURTESY: The Hindu, June 3, 2015
