Eveything you need to know about hair color and how genes affect hair color

Genetics of hair color
Parental Genes
Black Hair Color
Brown hair
Red Hair
Blonde Hair
Conditions affecting hair color
Aging or achromotrichia
Oxidative stress
Smoking and ultraviolet radiation effects
Medical conditions

Hair color is the pigmentation of hair follicles, more commonly known as the roots of the hair. Hair pigmentation is due to two types of melanin: eumelanin and pheomelanin.

Generally speaking, if there is more eumelanin, hair is darker. Pheomelanin is present when a person has lighter hair or skin. An abundance of eumelanin gives people black or brown hair, whereas an abundance of pheomelanin gives people red hair.

Melanin level is not constant. As it differs over time, it can cause hair color to change. It is also possible for one person to have hair follicles of more than one color.

As people grow older, fewer pigment cells will be around to produce melanin. Eventually, hair will look completely gray.

Some people’s hair turns gray at a very young age whereas others start to see their first gray hair in their 30s or 40s.

Hormones, certain medications, and chemicals such as hair relaxers can alter the characteristics of a person’s hair.

Many ongoing researches are trying to resolve the complex relationship between genetics and human hair.

Hair colors are also usually associated with ethnic groups. For example, people living in Northern and Eastern Europe mainly have blonde colors; whereas Asian, Melanesian and African people are characterized by darker colors.

Genetic factors appear to play a major role in the density, length, color and texture of hair. Studies suggest that different genes influence hair texture and thickness in people belonging to different ethnic backgrounds.

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Genetics of hair color

MC1R is the best-studied hair color gene in humans. The MC1R gene contains the information needed to make functional protein called the melanocortin 1 receptor, which plays a vital role in normal pigmentation.

The melanocortin 1 receptor is found mainly on the surface of melanocytes, the specialized cells that secrete the pigment called melanin.

Skin, hair, and eyes get their color from melanin. Melanin also plays a role in normal vision as it is also found in retina, which is the light-sensitive tissue at the back of the eye.

Melanocytes make both eumelanin and pheomelanin. When MC1R is activated, eumelanin is produced, which causes the hair to be dark. Known as a UV absorbent, Eumelanin protects the skin from damage by ultraviolet radiation. When MC1R is not activated or blocked, the melanocytes produce pheomelanin, which results in light or red hair.

This pigment lacks the feature of protecting the skin from sunlight. Pheomelanin is photounstable and may even promote carcinogenesis. MC1R is a key gene in normal human pigmentation, yet researchers believe that other genes also contribute to a person's hair and skin coloring. Some of these genes, including ASIP, DTNBP1, GPR143, HPS3, KITLG, MLPH, MYO5A, MYO7A, OCA2, SLC45A2, SLC24A5, TYRP1, TYR, ERCC6, GNAS, HERC2, IRF4, OBSCN, SLC24A4, TPCN2, and MITF, have a role in the production process of melanin in hair. Some genes are associated with gene transcription (DNA to RNA), DNA repair, the transport of substances (such as calcium) across cell membranes, or the structure of hair follicles.

Parental Genes

The genetics of hair colors are not yet firmly established, but we know each child inherits eight genes (four hair-color genes from each parent). Genes of eumelanin are either "off" or "on." For example, using the representative letter "A," a large A will be an "on" gene, while a lowercase a will be an "off" gene.

The mom contributes AAaa while the dad contributes AAAA. The result for the child will be AAAAAAaa, meaning a child will have dark hair. The more "on" A genes a child receives, the darker the resulting hair color will be and the tighter the granules will be packed together.

Phenomelanin is passed down via a different gene known as an allele.

Only European-Americans carry this gene. If a parent has these alleles (especially if she has blond or red hair), these alleles will likely be passed down. Yet, if a significant amount of eumelanin is present, this will be expressed more than the phenomelanin.

Hair color is based on the number of eumelanin or phenomelanin genes that are turned on — it’s a cumulative effect rather than all-or-nothing.

Black Hair Color

Throughout the world, black hair is the darkest and the most common of all hair colors, because many populations have this dominant genetic trait. It is found in people of all backgrounds and ethnicities, it has large amounts of eumelanin, and is denser than other hair colors. Most people in Asia, pre-Columbian Americas and Africa have black hair.

Brown hair

Brown hair is considered the second most common human hair color, after black. There are various shades of brown hair such as brown-ebony, brown-mahogany, brown-oak, etc. Brown hair varies from light brown to almost black hair.

It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment pheomelanin.

Brown hair is mainly seen among populations in the Western world, especially among those from Central Europe, Southeastern Europe, Eastern Europe, Southern Europe, Southern Cone, the United States, and also some populations in the Greater Middle East where it transitions smoothly into black hair.

Additionally, brown hair is common among Australian Aborigines and Melanesians.

Red Hair

Phaeomelain is predominant in both the hair and the skin of individuals with red hair. They also have a reduced ability to produce eumelanin. This is why they fail to tan and shouldn’t be exposed to ultraviolet radiation.

According to this study , more than 80% of individuals with red hair and/or fair skin that tans poorly had MC1R gene sequence variants, whereas fewer than 20% of individuals with brown or black hair had the gene, and it was also found in less than 4% of those who showed a good tanning response.

Red hair is the least common hair color in the world, as people with red hair represent only 1–2% of the population. Red hair is mainly associated with Celtic nations.

It is found in the British Isles, Scotland, which has the highest number of redheads, and in the northern and western fringes of Europe.

Blonde Hair

Blonde hair is very rare in humans. Blond hair people are only found in Europe and Oceania. Blonde hair has small portions of pheomelanin and eumelanin. In another way, if a small percentage of a person’s eumelanin and pheomelanin genes are activated and most are deactivated, he or she will produce only a little pigmentation and have blonde hair (or, if there’s some phaeomelanin thrown in, strawberry blonde hair).

Conditions affecting hair color

Aging or achromotrichia

Achromotrichia, which is the graying of hair with age, normally starts in the early to mid-twenties in men and late twenties in women. Hair graying is a natural age-associated process. This trait is closely related to chronological ageing, but its degree varies in all individuals.

As we grow old, hair turns grey, and then white. Genetics play a vital role in the age at which gray hair starts to appear.

Premature graying may occur alone as an autosomal dominant condition or in association with various autoimmune or premature aging syndromes.

Premature graying may reflect a genetically regulated early exhaustion of the melanocyte reservoir's seeding potential, or some defect in cell activation/migration associated with environmental factors, inflammation, or psychological stress.

Finding of this current study suggests that loss of melanocyte stem cells can be seen and temporarily precedes the loss of differentiated melanocytes in the hair matrix.

As the age of onset of premature graying is dependent more on the genotype of the individual, it is subject to racial variation. In caucasians, the average age of onset is 34 ± 9.6 years, whereas in black individuals it is 43.9 ± 10.3 years.

In japanese men, hair graying starts between 30 and 34, and between 35 and 39 in women. On an average, caucasians begin to gray in their mid-30s, Asians in their late 30s, and Africans, latest in their mid-40s.

A recent study reported that 6-23% of people have 50% gray hair by 50 years of age. Graying can be observed early in those with dark hair, but fair-haired individuals appear totally gray earlier. Both sexes are equally affected.

In men, graying usually begins at the temples and in the sideburns.

Later it spreads to the vertex and the remainder of the scalp, affecting the occiput last. Women usually start graying around the perimeter of the hairline.

Genetics identifies the rate at which a person turns gray.

It is common to observe kinships with marked early graying. The rate of graying varies, not only on different areas of the scalp but also in the body.

Beard and body hair are affected later. Chest, pubic, and axillary hair may remain pigmented even in old age.

Research findings suggested that temporal and occipital areas gray more in men than in women.

Graying usually begins in the temporal area in men but in the frontal area in women. The age of onset affects the involved scalp regions.

The parietal or occipital area was more involved at onset in early-onset group, whereas frontal area was more involved initially in late-onset group. Early onset did not mean faster progress.

But, grayness becomes very fast after the fifth decade regardless of age at onset. Graying of hair is usually continuous and persistent, but there are occasional reports of spontaneous repigmentation of gray hair, and partial, spontaneous reversal of premature graying may occur during the early stages of it.

Gray hair is believed to be rougher, stiffer, and less controllable than pigmented hair. Research findings suggested that gray hair is seriously harmed by UV damage and needs more UV protection than dark brown hair.

Gray hair often fails to hold a temporary or permanent set, and cannot properly absorb artificial color possibly due to changes in the underlying construction of the hair fiber.

Thickness, growth rate, and hair shaft elongation in non-melanized hair are significantly greater than in melanized hair.

White beard hair grows up to four times and has thicker hair shafts than pigmented beard hair. Besides, removing gray and white facial hair by laser becomes very complicated due to lack of melanin chromophore.

Oxidative stress

Experimental evidence showed that oxidative stress plays a major role in the ageing process.

Reactive oxygen species are activated by a large number of endogenic and environmental challenges.

Reactive oxygen species or free radicals are highly reactive molecules that can directly damage cellular structural membranes, lipids, proteins, and DNA.

The body possesses endogenous defense mechanisms, such as antioxidative enzymes and non-enzymatic antioxidative molecules, protecting it from free radicals by reducing and neutralizing them.

With age, the production of free radicals increases, while the endogenous defense mechanisms weaken.

This imbalance leads to the progressive damage of the structure of the cell, which results in the ageing phenotype.

As manifestation of hair aging, both melanocyte function and hair production or alopecia decrease.

There is strong proof that oxidative stress may be a main reason for both hair graying and hair loss.

New studies on how to overcome oxidative stress could help with the intervention and reversal of the hair graying process and age-dependent alopecia.

Smoking and ultraviolet radiation effects

Results of this research suggest that there is a relationship between smoking, hair graying and alopecia in men.

As for women, numbers were not sufficient to reach any significant conclusion.

An association of smoking status with androgenetic alopecia has been recently proved in an Asian community: smoking status, current number of cigarettes smoked, and smoking intensity were statistically detectable agents responsible for androgenetic alopecia in men after controlling for age and family history.

So far, there is no sufficient data about women or partners of heavy smokers via secondary inhalation.

When scalp hair gets thin due to age, the scalp becomes more vulnerable to ultraviolet radiation. While it has been recognized that at least 50% of ultraviolet radiation induced damage to the skin is due to the formation of free radicals, the effects of ultraviolet radiation on hair have received less attention.

This study suggested that photochemical impairment of the hair includes deterioration and loss of hair proteins as well as deterioration of hair pigment.

Findings of this study suggests that ultraviolet B radiation is responsible for hair protein loss and ultraviolet A radiation is responsible for hair color changes.

Medical conditions

Albinism is a group of inherited disorders, where there is little or no melanin in human hair, eyes, and skin.

The hair is often white or pale blond. African or Asian people suffering from albinism usually have yellow, reddish or brown hair color.

After exposure to normal minerals by early childhood, hair color may become darker.

Vitiligo is an acquired skin disorder caused by the disappearance of pigment cells from the epidermis that gives rise to well defined white patches on the hair and skin.

The shortage of melanin pigment makes lesions more vulnerable to sunburn.

Childhood malnutrition has been proven to be a reason for a reduction in the total melanin content of scalp hair.

Finding of this study suggests that a lack of melanin content is related to periods of malnutrition.

It is possible that reduced intake or availability of tyrosine, a key substrate in melanin synthesis, may decrease hair melanin content during periods of malnutrition.

Malnutrition is also known to cause hair to become lighter, thinner, and more brittle Werner syndrome is a rare progressive disorder whereby the process of aging is accelerated in an unusual manner.

According to National Organization for Rare Diseases (NORD), those with the disorder typically experience early graying and premature loss of scalp hair by age 25.

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