• Hair color - what is it
• Hair color - what is it references

Hair color - what is it

Hair fiber has no color, bleach any hair and the fiber looks white simply because it reflects light. Hair color is provided by pigments produced by cells called "melanocytes". The pigments are called "melanin". Melanin actually means black so strictly speaking we should only use this word when talking about black hair. However, today scientists and dermatologists use the word melanin when talking about any kind of hair pigment blonde, red, brown, or black.

In humans, melanocyte cells are found diffusely scattered in the skin and also in little clusters in the hair follicles. Melanocytes respond to various stimulants to produce more or less melanin. Sunlight exposure makes the melanocytes in the skin produce more pigment and we get a tan (unless you are of Celtic ancestry like me). In some other mammals, such as rats and mice, melanocytes are exclusively found located in hair follicles and not in the skin between the hair follicles. Rats and mice cannot get sun tans. But I digress. The melanocytes of the skin and the melanocytes of the hair follicles are essentially the same. It is thought that the melanocytes in hair follicles can act like a storage depot for supplying the skin with melanocytes. This becomes very apparent then the skin is damaged and depleted of melanocytes. Studies show the melanocyte cells migrate from the hair follicles to repopulate the melanocyte deficient skin.

Melanocytes in hair follicles are primarily located in the hair bulb at the bottom of hair follicles. They sit in a group just above the dermal papilla along with the matrix cells that produce the hair fiber. For the melanocytes, this is the ideal location to produce pigment and have it incorporated into the growing hair fiber. There are melanocytes located in other regions of the hair follicle such as the root sheaths that surround the hair fiber. However, it is thought that these melanocytes do not significantly contribute to coloring the hair fiber.

Melanocytes produce melanin pigment proteins in their cell cytoplasm. The pigment is accumulated in membrane bound vesicles in the cell called "melanosomes". Melanocytes are usually very easy to identify in a skin biopsy because they are full of these melanosomes. In black hair producing follicles, the melanosomes in the melanocytes are very large oval shaped and gradually become densely filled with pigment proteins. People with lighter colored hair have less melanin protein in their melanosomes. Blonde haired people have melanosomes with a low density and patchy deposition of melanin. People with red and blonde hair have melanosomes that are smaller and spherical in shape and the individual melanin pigment granules inside the melanosomes are also smaller.

The matrix keratinocytes that produce the hair fiber cluster around the melanocyte cells. The melanocyte cells release their melanosomes to the keratinocytes through dendritic processes. The keratinocytes actively phagocytose the melanosomes (which means the keratinocytes "eat" the melanosomes by surrounding them and pulling them into the cell). Once the keratinocyte cells have melanosomes inside them they are then formed into the hair fiber and thus the hair fiber has color.

 

Above is a whole hair follicle that has been dissected from the skin of a man with dark brown hair. In the hair follicle bulb you can see a mass of brown melanin and above this the hair fiber. The melanocytes full of pigment and the adjacent keratinocytes are actually in an upturned cup shape (think in 3D) that sits over the pear shaped dermal papilla. You can the bottom of the pear shaped dermal papilla below the mass of brown pigment. As the hair fiber grows, the mass of brown pigment will be incorporated into the hair fiber cells.

Hair color - what is it references

• Commo S, Bernard BA. Melanocyte subpopulation turnover during the human hair cycle: an immunohistochemical study. Pigment Cell Res. 2000 Aug;13(4):253-9.
• Tobin DJ, Slominski A, Botchkarev V, Paus R. The fate of hair follicle melanocytes during the hair growth cycle. J Investig Dermatol Symp Proc. 1999 Dec;4(3):323-32.
• Horikawa T, Norris DA, Johnson TW, Zekman T, Dunscomb N, Bennion SD, Jackson RL, Morelli JG. DOPA-negative melanocytes in the outer root sheath of human hair follicles express premelanosomal antigens but not a melanosomal antigen or the melanosome-associated glycoproteins tyrosinase, TRP-1, and TRP-2. J Invest Dermatol. 1996 Jan;106(1):28-35.
• Schallreuter K, Slominski A, Pawelek JM, Jimbow K, Gilchrest BA. What controls melanogenesis? Exp Dermatol. 1998 Aug;7(4):143-50.
• Tobin DJ, Hagen E, Botchkarev VA, Paus R. Do hair bulb melanocytes undergo apoptosis during hair follicle regression (catagen)? J Invest Dermatol. 1998 Dec;111(6):941-7.
• Boissy RE and Nordlund JJ. Biology of melanocytes. In: Cutaneous Medicine and Surgery. Arndt KA, LeBoit PE, Robinson JK, and Wintroub BU, eds. W.B. Saunders Co: Philadelphia, 1996, pp.1203-1218.
• Slominski A, Paus R, Plonka P, Chakraborty A, Maurer M, Pruski D, Lukiewicz S. Melanogenesis during the anagen-catagen-telogen transformation of the murine hair cycle. J Invest Dermatol. 1994 Jun;102(6):862-9.
• Slominski A, Paus R. Melanogenesis is coupled to murine anagen: toward new concepts for the role of melanocytes and the regulation of melanogenesis in hair growth. J Invest Dermatol. 1993 Jul;101(1 Suppl):90S-97S.
• Ortonne JP, Prota G. Hair melanins and hair color: ultrastructural and biochemical aspects. J Invest Dermatol. 1993 Jul;101(1 Suppl):82S-89S.
• Prunieras M. Melanocytes, melanogenesis, and inflammation. Int J Dermatol. 1986 Dec;25(10):624-8.
• Jimbow K, Ishida O, Ito S, Hori Y, Witkop CJ Jr, King RA. Combined chemical and electron microscopic studies of pheomelanosomes in human red hair. J Invest Dermatol. 1983 Dec;81(6):506-11.
• Garcia RI, Szabo G. Modulation of melanosome ultrastructure in cultured embryonic pigment cells. J Exp Zool. 1983 Feb;225(2):285-91.
• Brown AC, Pollard ZF, Jarrett WH 2nd, Olkowski ZL. White hair: genetic and immunologic implications. Birth Defects Orig Artic Ser. 1982;18(1):1-20.
• Jimbow K, Roth SI, Fitzpatrick TB, Szabo G. Mitotic activity in non-neoplastic melanocytes in vivo as determined by histochemical, autoradiographic, and electron microscope studies. J Cell Biol. 1975 Sep;66(3):663-70.
• Kukita A, Sato S, Ito K. Electron microscopic observations of melanin transfer in human skin. Evidence for indirect melanin transfer. Acta Derm Venereol. 1974;54(5):349-57.
• Jimbow K, Fitzpatrick TB. Characterization of a new melanosomal structural component--the vesiculoglobular body--by conventional transmission, high-voltage, and scanning electron microscopy. J Ultrastruct Res. 1974 Aug;48(2):269-83.
• Hearing VJ, Phillips P, Lutzner MA. The fine structure of melanogenesis in coat color mutants of the mouse. J Ultrastruct Res. 1973 Apr;43(1):88-106.
• Mahrle G, Orfanos CE. [Hair colour and hair pigment. Electronmicroscopic investigations on natural and bleached hair] Arch Dermatol Forsch. 1973 Dec 5;248(2):109-22.
• Snell RS. An electron microscopic study of melanin in the hair and hair follicles. J Invest Dermatol. 1972 Aug;59(2):144-54.
• Snell RS. An electron microscopic study of melanin in the hair and hair follicles. J Invest Dermatol. 1972 Apr;58(4):218-28.
• Jimbow K, Takahashi M, Sato S, Kukita A. Ultrastructural and cytochemical studies of melanogenesis in melanocytes of normal human hair matrix. J Electron Microsc (Tokyo). 1971;20(2):87-92.
• Orfanos C, Ruska H. [Fine structure of human hair. 3. Hair pigment] Arch Klin Exp Dermatol. 1968;231(3):279-92.
• Hadley ME, Quevedo WC Jr. Vertebrate epidermal melanin unit. Nature. 1966 Mar 26;209(30):1334-5.