Hair color is a form of pigmentation, determined by natural pigments produced within the hair follicles. The specific shade and tone of an individual’s hair are influenced by these pigments. These pigments can change over a person’s lifetime due to various internal and external factors, leading to shifts in hair color.
The Science of Hair Color
Hair color originates from specialized cells called melanocytes, located within the hair follicles. These cells produce melanin, the pigment responsible for coloring hair.
There are two primary types of melanin that determine hair color: eumelanin and pheomelanin. Eumelanin provides black and brown shades, with higher concentrations resulting in darker hair. Pheomelanin contributes to red and yellow tones. The combination and ratio of these two melanin types, alongside their total amount, create the diverse spectrum of human hair colors. Black and brown hair contain significant amounts of eumelanin, while red hair has a higher concentration of pheomelanin.
Why Hair Turns Gray or White
Hair often turns gray or white, a process primarily linked to the activity of melanocytes within the hair follicles. Hair turns gray or white when these melanocytes slow down or stop producing melanin altogether.
One factor in graying is the behavior of melanocyte stem cells (McSCs). These cells regenerate pigment-producing melanocytes in each new hair growth cycle. As individuals age, these stem cells can become “stuck” in the hair follicle, preventing them from maturing and migrating to produce new pigment cells. This means fewer melanocytes are available to color the growing hair strands.
Furthermore, the accumulation of hydrogen peroxide within hair follicles contributes to the loss of hair color. Hydrogen peroxide is a byproduct of metabolism, and its levels increase with age. The body’s ability to neutralize this compound declines because the enzyme catalase, which breaks down hydrogen peroxide, becomes less concentrated in aging cells. This excess hydrogen peroxide interferes with tyrosinase, an enzyme essential for melanin synthesis, effectively bleaching the hair from within. Genetics also plays a role in when and how quickly hair greys, influencing the timing and progression of these cellular changes.
Environmental and Lifestyle Influences
External factors and daily habits can influence hair color, though less dramatically than the natural graying process. Sun exposure, particularly UV radiation, can alter hair pigmentation. UV rays penetrate the hair shaft and break down melanin pigments, causing hair to lighten or fade. This lightening effect is often more pronounced in individuals with lighter hair colors, such as blondes and redheads, because their pheomelanin is more susceptible to UV damage. Darker hair may experience dulling or a loss of richness due to melanin degradation, though the change might be less noticeable.
While diet does not directly change existing hair color, severe nutritional deficiencies can impact hair health and appearance. Adequate intake of certain vitamins and minerals, such as copper, iron, and zinc, supports healthy melanin production. Copper, for example, is essential for the activity of tyrosinase, an enzyme vital for melanin synthesis. Deficiencies in these nutrients can contribute to premature graying or other pigmentation changes.
Hormonal and Medical Factors
Internal physiological changes and medical conditions can alter hair color. Hormonal fluctuations, such as during pregnancy or due to thyroid imbalances, can result in subtle changes to hair texture or color. These shifts are typically temporary and resolve once hormone levels stabilize.
Medical conditions can directly impact hair pigmentation. Vitiligo, an autoimmune condition where the immune system attacks melanocytes, causes patches of skin and hair to lose color, often turning white or gray. This can affect hair on the scalp, eyebrows, eyelashes, or beard.
Certain medications can cause hair color changes as a side effect. Chemotherapy drugs can alter hair color, and others, like chloroquine, have been associated with hair lightening. These drug-induced changes are often reversible once the medication is discontinued.