See also chemistry of hair explained

Kemin Technologies

The hair follicle is a dynamic tissue that cycles between an on-state (anagen) and off-state (elogen). There are three major compartments, the hair shaft (medulla, cortex and cuticle), the inner root sheath (cuticle, Husley’s lyaer and Henle’s layer) and most peripheral, the outer root sheath.  At the common base of these compartments are the pluripotential matrix cells that give rise to teh hair shaft and inner root sheath through differentiation. Beneath these matrix cells are a group of mesenchymal-derived cells that form the dermal papilla which play an important role in inducing hair follicle neogenesis. (Bertolino, “Differential Expression of Type I Hair Keratins” J Invest Dertmatol 94: 297-303, 1990).

Hair Saft

The hair shaft consists of an outer cuticle surrounding a central cortex which may contain a central medulla. (Folin, Forensic Science International 83 (1996) 191-199).

Hair consists of : (1) an outer cuticle wrapping and protecting the hair fiber: (2) a cortex (the hair fiber itself): The cortex is composed mainly of 3 different types of proteins: fibrous keratins which constitute filaments, non-fibrous matrix proteins and cell membrane peripheral proteins. (3) a central medulla. 

Cortex: of animals hairs, which represents about 85% of the fiber weight, is made up of microfibrils embedded in a matrix of high-sullphur and high-glycine and tyrosine proteins. Microfibrils are composed of closely packed intermediate filaments (IF) arising from the interaction of type I and Type II keratins. Comparisons of the amino acid sequences of keratins show that the central rod domains, containing about 310 amino acid reisudes, are highly conserved while the N- and C-terminal end domains of Type II deratins exhibit appreciable species specific differences, which can be exploited to produce monoclonal antibodies that react exclusively with the hair fibers from a given animal. For example, Paluzzi (“anti-keratin monoclonal antiboides for identifying animal hair fibers” Textile Research Journal 2004, 74: 458) dislose large difference in the immunoreaction with keratins from cashmere compared with those from wool.

Cuticle: In the hair follicle the uticle develops as a thin layer of cells between the hair shaft cortex and the inner root sheath. Once the cuticle cells begin to differentiate they accumulate cysteine rich, glycine rich keratins in their cytosol (Jenkins, J Invest Dermatol, 1994, 103(3), 310-7).

surface of hair: is composed of the protein Keratin, containing both acidic and basic amino acids. The amino acid composition of keratin is such that at natural pH values, the hair possesses a net negative charge. (US2,067,499).

Hair Follicle (HF): 

The part of the hair base embedded in the skin is called the hair follicle and consists of plural different tissues. It is involved in the differentiation and growth of hairs. HFs regenerate by repetitive hair growth cycles (see below) and produce hair fibers during postnatal life.

Dermal papilla (DP): is envoloped by the dermal sheath in the hair bulb of a hair folicle (HF). The DP consists of specialized mesenchymal Dermal papilla cells (DPC) which control the development of hair folicles via-cell-cell interactions and extracellular molecules. The DP controls the hair growth cycle and directs hair bulb matrix epithelial cells to differentiate to produce hair fiber. Secretion factors of DPs also participate in controlling the HF morphogenesis and regulate the phase transition of hair growth cycle, such as fibroblast growth factor.

Hair Growth Cycle:

Anagen: The first cycle, known as anagen, the follicle is generated and new hair grows. When a new hair cycle is initiated, it is thought that a signal from the dermal papilla stimulates the stem cells, which are thought to reside in the permanent portion of the follicle, to undergo a phase of downward proflieration and genesis of a new bulbous base contianing matrix cells which then surround the dermal papilla. As a new anagen state progresses, these hair matrix cells produce a new hair. Each follicle appears to be under completely asynchronous control, resulting in a continuum of follicles in anagen, catagen, and telegen phases, leaidng to a relatively homeogenous hair distribution.

Catagen: During the second stage, the follicle elongation ceases and the follical regresses because the matrix cells stop proliferating. At this stage, the lower, transient half of the follicle is eliminated due to terminal differentiation and keratinization, and programmed cell death. Also during catagen, although the dermanl papilla remains intact, it undergoes several remodeling events, including degradation of the extracellular matrix that is deposited during analgen. At the close of catagen, the hair is only loosely anchored in a matrix of keratin, with the dermal papilla located just below. The catagen stage occurs at a genetically predetermined time, which is specific for each hair type in a species.

Telogen: is characterized by the follicle entering a quiescent phase, during which the hair is usually shed.

Hair Care:

Protect your hair by shampooing every other day instead of daily. Shampoos and excess shampooing can strip hair of moisture. Use warm water and a mild shampoo with sunscreen. Apply extra conditioner to keep your hair hydrated, shiny, and soft. Don’t overstyle with the blow dryer or flat iron. And protect your hair from the elements by wearing a hat.