Hair color is determined by the melanocytes found only in the matrix area of the follicle at the base of the cortex directly above the follicular papilla. Melanocytes transfer packages of melanin (melanosomes) to the cortical cells during anagen. Eumelanin is the dominant global pigment and confers black/brown hair. Pheomelanin, a mutation of eumelanis, is the predominant pigment found in blonde or red hair. Graying of hair is a normal manifestation of aging and illustrates progressive reduction in melanocyte function. The proportions of eumelanin and pheomelanin and the total amount of melanin determine the fi nal natural color of the hair.
Black and dark brown hair are the prevalent natural hair colors of peoples of all regions, accounting for more than 90% of all human hair. Dark hair is characterized by very high levels of the dark pigment eumelanin.
Blonde hair frequency is reported as 1.8% worldwide. Blonde hair is characterized by low levels of the dark pigment eumelanin and higher levels of the pale pigment pheomelanin. Shades range from light brown to pale blonde. In certain European populations, the occurrence of blonde hair is more frequent, and often remains throughout adulthood, leading to misinterpretation that blondeness is a uniquely European trait. Based on recent genetic information, it is probable that humans with blonde hair became more numerous in Europe about 10,000 to 11,000 years ago during the last ice age, as a result of Fisherian runaway mechanisms. Prior to this, early Europeans had dark brown hair and dark eyes, as is predominant in the rest of the world. In humans of many ethnicities, lighter hair colors occur naturally as rare mutations, but at such low rates that it is hardly noticeable in most adult populations. Light hair color is commonly seen in children, and is curiously common in children of the Australian Aboriginal population.
Lithuania has the highest percentage of people with blonde hair. Bleaching of hair is common,
especially among women. Bleached blonde hair can be distinguished from natural blonde
hair by exposing it to ultraviolet light, as heavily bleached hair will glow, while natural blonde
hair will not.
There are no comparable data for red hair, but in the areas of obvious frequency (the fringes of Western and Eastern Europe) it is at a maximum of 10%. In Scotland, 35% of the population carries the recessive gene for red hair. Eighty percent of redheads have the melanocortin-1 receptor gene anomaly. Controversial estimations of the original occurrence of the red-haired gene at 40,000 years ago are probable.
Red hair is associated with the melanocortin-1 receptor, which is found on chromosome 16. Red hair may be an example of incomplete dominance. When only one copy of the red-hair allele is present, red hair may blend with the other hair color, resulting in different types of red hair including strawberry blonde (red-blonde) and auburn (red-brown).
