When the first few gray hairs pop up, they often cause full blown panic. Gray hair usually represents the first trumpets that herald the aging process.

A study published in 2012 reported that the average onset of graying occurs at age 40. The study also showed that the pattern of gray depends on your gender, your smoking habits and the age at which graying began.

The average onset may be 40, but some people go gray as early as puberty. In that case, going gray can’t just be because your hair follicles have gotten old. So why does hair turn gray?

First signs of gray hair

First signs of gray hair (Photo credit: Sean Dreilinger)

The Basics – Homeostatis

In order to understand what makes your hair turn gray, we need to start with understanding the basic underlying processes of the aging process. The first important concept in aging is homeostasis. Homeostasis is the name for the various processes your body goes through in order to keep everything running.

Homeostatic processes include:

  • Sweating or shivering to keep your body temperature in the optimal range
  • Replicating cells to heal wounds
  • Maintaining blood sugar levels

These things help to maintain a stable internal environment for your body. In order for your body to maintain the status quo at a cellular level, it needs a constant supply of new cells to repair injuries or other cellular damage. These new cells mainly come from adult stem cells that occur in adult tissues.

Stem cells normally come up in discussions about fetal development, but they play a big role in adult homeostasis as well. These cells have the potential to become any type of cell depending on the needs of the surrounding tissues. So say you get a cut that goes through several layers of skin; the stem cells in your skin tissues can grow into multiple types of skin cells or connective tissue in order to repair the damage.

Visible aging occurs when homeostasis cannot keep up with the amount of cells that need replacing. Certain cells types have different life spans, so often too many cells die all at once to be repaired by the stem cells available.

Are Melanocyte Stem Cells Responsible For Graying Hair?

melanocyte and melanin

Melanocyte and Melanin (Photo credit: Wikipedia)

Hair color is controlled and maintained by cells in the hair follicles called melanocytes. Melanocytes have the sole purpose of producing melanin. Melanin causes the different colors found in human skin, eyes and hair.

Melanocytes in terms of hair occur in the base of the hair follicle. The melanocytes transfer pigmentation to the newly growing hair stalk from the very bottom. Many people seem to think that graying occurs because of a malfunction in the cells of the follicle, but a review published in 2007 from the Department of Medicine at Stanford University reports that this is not the case. The review collects studies that point to melanocyte stem cells as the more likely offender.

About half-way up the hair follicle from the melanocyte region, an area called “the bulge” contains the melanocyte stem cells used to regenerate dead or injured melanocytes.

These melanocyte stem cells have the ability to maintain themselves in a way fully mature melanocyte cells do not. This causes them to survive longer than the functional melanocytes and stay available to replace any of them. The stem cells also have the ability to completely repopulate an entire set of melanocytes during the beginning stages of the hair follicle growth cycle.

Hair Aging

However, your body only has so many melanocyte stem cells. When a melanocyte dies or gets damaged, a stem cell must descend from the bulge in order to replace it. Damage can occur in a number of ways, from physical injury to the hair follicle to over exposure to sunlight. Over the course of a lifetime, your hair follicles go through a lot and have to replace a huge number of melanocyte cells.

Leaving damage aside, normal hair follicles go through several full death and re-growth cycles in a life time. Each growth cycle means that the melanocyte cells get completely replaced by their stem cells. All of these replenishments use up a lot of stem cells. Eventually, the follicle runs out.

When the follicles run out of stem cells, the melanocytes continue to die, but no longer get replaced. This leads eventually to the hair follicle lacking the ability to add color to the hair stalks that continue to grow from the follicle.

How Your Hair Turns Gray

Gray hair begins to grow simply because it contains no melanin and therefore no color at all. Most often this happens around the 7th to 15th growth cycle of the follicle, which can happen any time between ages 36 to 50. This depends on many factors, such as gender and smoke habits as mentioned before, as well as race and behaviour.

This can help explain why some people go gray earlier than others. It mainly depends on how many melanocyte stem cells you are born with, and how quickly that stockpile depletes from normal aging or damage, not from malfunctioning cells.

Even though we can lay the blame on lack of stem cells for hair graying, some things remain unclear. As of the publishing of the 2007 review, no one really knows what exactly causes more rapid damage of the fully mature melanocyte cells. If the main source of damage to melanocytes was more well understood, it could lead to treatments or prevention of damage to those cells. People could stave off gray hair and keep their natural hair color as long as possible.

As it is though, most people turn to chemical dyes in order to add pigment to their gray hair to cover up the aging process, or simply because they want a different pigment than the one described in their genes. It works well enough, but I suspect that many people would throw ridiculous amounts of money at any treatment that let them keep their hair color in a more natural way.


Jo, S. J., Paik, S. H., Choi, J. W., Lee, J. H., Cho, S., Kim, K. H., Eun, H. C. & Kwon, O.S. (2012) Hair graying pattern depends on gender, onset age and smoking habits. Acta Derm Venereol 92(2) 160-161.

Sarin, K. Y. & Artandi, S. E. (2007) Aging, graying and loss of melanocyte stem cells. Stem Cell Rev. 3(3) 212-217.