What Causes Grey Hair?

Of all the physical changes we experience, finding that first strand of grey hair is often one of the most memorable. It seems to appear overnight, a silvery interloper in a field of familiar color. For centuries, this transformation has been associated with wisdom, stress, or simply the inevitable march of time. But what is actually happening at a biological level to cause our hair to lose its color? The answer is a fascinating interplay of genetics, cellular biology, and lifestyle factors.

The process doesn’t actually involve hair “turning” grey. Rather, each new hair that grows from a follicle has the potential to grow with or without pigment. The color of your hair is determined by specialized cells called melanocytes, which are located at the base of each hair follicle. These tiny cellular factories produce a pigment called melanin. As a new hair shaft is constructed from keratin proteins, these melanocytes inject melanin into it, giving the hair its specific shade—be it black, brown, blonde, or red.

There are two main types of melanin that combine to create your unique hair color: eumelanin, which is responsible for black and brown shades, and pheomelanin, which produces red and yellow tones. The specific ratio and concentration of these pigments, dictated by your genes, determines the exact color of your hair. A grey hair, therefore, is simply a hair with a very minimal amount of melanin, while a white hair is one with no melanin at all. The appearance of “grey” is often an optical illusion, created by the mixture of these unpigmented hairs among the still-pigmented ones.

So, the central question is not what turns hair grey, but what causes the melanocytes to stop producing and transferring melanin to the hair shaft?

The Primary Driver: Genetics and Natural Aging

By far the most significant factor in when you will start to go grey is your genetic inheritance. Think of your hair follicles as having a pre-programmed biological clock. Your genes dictate the timeline for when your melanocytes will begin to slow down their production and eventually expire. This is why a tendency to grey early or late often runs in families. If your parents went grey in their thirties, there is a strong probability that you will follow a similar pattern.

This genetic timeline is also linked to ethnicity. On average, people of Caucasian descent tend to begin greying in their mid-30s. Those of Asian descent typically see their first grey hairs in their late 30s, while people of African descent often don’t see significant greying until their mid-40s.

This process is intrinsically linked to natural aging. Over time, the population of melanocyte stem cells that reside within the follicle begins to dwindle. These stem cells are responsible for replenishing the follicle with new, pigment-producing melanocytes for each hair growth cycle. As we age, these stem cells get exhausted or damaged. Eventually, the reservoir runs dry. When a follicle is left with no melanocytes, any hair it produces from that point on will be white.

The Role of Stress in Accelerating the Process

The long-held belief that a sudden shock or a period of intense stress can cause someone to “go grey overnight” has some basis in science, though not in the way most people imagine. Stress does not cause existing colored hairs to lose their pigment. What it can do is accelerate the depletion of those precious melanocyte stem cells.

When the body is under stress, it activates the “fight-or-flight” response, releasing a chemical called norepinephrine into the follicle. Recent research has shown that this chemical can cause the melanocyte stem cells to activate and convert into pigment-producing cells far too rapidly. This essentially burns through the follicle’s entire reserve of stem cells prematurely. The existing hair falls out as part of its natural cycle, but when the new hair begins to grow, there are no stem cells left to create new pigment cells. The result is a new hair that grows in white. This is also linked to a condition called telogen effluvium, where significant stress causes a large number of hairs to fall out at once. When they regrow, they may appear greyer because the newly grown, unpigmented hairs are more noticeable.

Lifestyle and Health Factors

While you can’t change your genes, certain external factors and health conditions can influence premature greying.

Oxidative stress is a key contributor. This occurs when there is an imbalance between free radicals—unstable atoms that can damage cells—and the antioxidants that neutralize them. This cellular damage can impact the health and longevity of melanocytes. Factors that increase oxidative stress include smoking, pollution, and a poor diet. In fact, numerous studies have shown a direct link between smoking and the onset of premature greying before the age of 30.

Specific nutritional deficiencies can also disrupt melanin production. A lack of Vitamin B12 is one of the most well-documented culprits. Deficiencies in minerals like copper, iron, and zinc can also interfere with the biochemical pathways required to create melanin. In some cases, if the greying is caused by a correctable deficiency, restoring proper nutrient levels may help return color to new hair growth.

Finally, certain medical conditions, particularly autoimmune diseases that attack the skin and hair like alopecia areata and vitiligo, can damage melanocytes and lead to patches of white hair. Thyroid disorders have also been linked to premature greying.

Ultimately, going grey is a natural and complex biological process, guided primarily by the genetic hand you were dealt. While we can’t stop time, understanding the science behind it reveals that this change is more than just a cosmetic shift—it’s a window into the intricate cellular mechanics that define how we age.