You can classify grey hair into two types:
1.) Grey hair that occurs with increasing age
2.) Premature grey hair that occurs long before the appropriate age sets in. Some say premature greying is considered applicable where over 50% of your hair is grey before the age of 40.
The causes of grey hair in each of these instances often differ.
What age is normal for hair to go grey?
There comes an age when it is expected to see a grey hair or two without it being considered “premature greying”.
Whilst it’s true that this age differs from person to person depending on their genetics and race, statistics show that around a white-skinned person’s late 20s to early 30s, the first grey hairs are often seen. Dark-skinned races often have an extra grace period of about 10 years before their first greys set in.
Past the age of 30, each decade sees an increased 10-20% risk of gaining grey hairs.
Whilst it is considered premature greying for a person to have 50% grey hair before the age of 40, if this is the case by the age of 50, it is considered quite normal.
But why do hairs go white with age?
Causes of grey hair with increasing age
In order for hair to have colour, it must have the pigment molecule melanin in the hair follicle. Melanin is produced by special cells called melanocytes. The melanocytes pass the pigments they make to the nearby cells called keratinocytes whose job it is to build the pigments into the hair.
With increasing age, it has been observed that melanocytes die off, so that they no longer pass pigment to the hair. Without a pigment present, the hair appears white. The question is:
Why do the melanocytes die as you get older?
To answer this question we first need to ask: What makes the melanocytes?
The answer is: stem cells.
Stem cells are special cells because they are often pluripotent, meaning that they have the potential to turn into a wide range of other cells (pluri = many; potent = potential). In other words, stem cells are like an immature bud-cell which can grow up to become one of many cell types. One of the cell types that it can become is the melanocyte.
When melanocytes die as you get older, what happens to the stem cells from which they grow? Researchers have found that as people grow older, the number of stem cells in the location where they differentiate into melanocytes, also decreases.
Why do these stem cell numbers decrease with age?
Research is still trying to come up with answers.
One clue may be in a recent discovery of the role of a protein called Wnt, which is important for the interaction and signalling between stem cells. Insufficient Wnt protein has been associated with inhibition of melanocyte stem cell activation.
If decreased Wnt signalling is behind grey hair, it’s a good question to ask: Why would Wnt signalling at these stem cells be decreased with increasing age?
Wnt may be inhibited from being formed or it may be inhibited from carrying out its functions in spite of being around, but these questions are still under research.
If you’d like to have a go at solving the great Wnt mystery, you can start by reading more about the Wnt signalling pathway here although it gets extremely technical.
The bottom line on why do we get grey hair as we get older
At the time of this article, we don’t really know! But it seems to be something to do with the reasons behind Wnt protein signalling pathways being disrupted with age.
Theories about why we adapted to get grey hair with age
Although we don’t fully understand the biological mechanisms, this doesn’t stop us from hypothesizing about why it might be a beneficial evolutionary change to have grey hair with increasing age.
The main theory regarding why older humans have grey hair parallels one of the main theories of why we age.
This theory of ageing is that the longer we are around on Earth, the more time there is for oxidation, and wear and tear of cells to build up over time.
It could be that the drivers behind hair pigment formation (melanocytes, melanocytes stem cells and components of the Wnt signalling pathway) are also affected by accumulating cell damage that occurs with age. In this sense, greying hair may be a mechanism brought on by the removal of damaged cell components somewhere deep in the pathway that determines hair coloration. Since the removal of damaged cell components is protective of the body, it may be that the greying of hair is therefore a side effect of this safety mechanism in our body.
This theory is consistent with the fact that grey hair happens as we reach more mature years (by which time we are more likely to accumulate DNA damage). It is also consistent with the observation that greying of hair increases with smoking, hair-bleaching and excess sun exposure, all of which increase risk of oxidation, DNA and cell damage.
If oxidation is the driver behind the greying of hair, then avoidance of oxidizing activities that produce free radicals should reduce greying of hair. Such activities include smoking, excess sun exposure, exposure to hydrogen peroxide, excess exposure to ozone, exposure to radiation e.g. X-rays, excess consumption of oxidizing minerals like iron and copper (although you need sufficient levels for good health), and excess consumption of pro-oxidative foods like sugar.
Even if it doesn’t reduce grey hair, avoiding free radical formation is good practice for maintaining optimal health. Similarly, eating plenty of antioxidants may also be helpful.
You can read more about drivers of greying hair in the companion article on premature greying. It may be that some drivers of premature greying also contribute to greying of hair at more appropriate ages.
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