Your hair follicle adheres to a genetically programmed schedule that includes growth, resting and hair shedding, then the regrowth of new hair. During its lifetime, a human hair goes through three stages:

Stage 1 - Anagen

Scalp hair follicles enter the hair growth phase and synthesize hair for a period of 2 - 5 years at a rate of about 6 inches (15 cm) per year. Thus a hair 2 feet (60 cm) in length would be about four years old at the end, and only a month or so old near the scalp. In general, 85% of the scalp hair is in the anagen phase. Eyelash follicles, and the follicles for hair on your arms and legs, have a growth stage lasting only a few months, the resultant hairs that they produce are short.

Stage 2 - Catagen

This is a short transitional stage, The follicle becomes physically smaller as the lower portions of the follicle are absorbed by the body, and ceases to make hair.

Stage 3 - Telogen

A resting stage lasting two to four months, after which it sheds the hair shaft. Only 15% of your hair is resting at any one time. The hair follicle relaxes its hold on the hair shaft bulb, and the bulb of the hair shaft moves closer to the surface of the skin. Over time the hair shaft loosens and eventually the hair is shed. At the end of the resting stage, the old hair falls out, the follicle enlarges, and a new growth cycle starts and a new hair shaft begins to grow.

The Structure of Hair

Mature hairs are biologic filaments composed primarily of proteins (88%) of a hard, tough, insoluble, fibrous type known as keratin. Proteins are built up from individual amino acids to form long chains where each amino acid is a link in the chain. Two amino acids are joined together by a "peptide bond", and the correct number of amino acids placed in their correct order will form a specific protein; i.e. keratin, collagen, elastin, and so on. The keratin found in human hair is also a major protein in fingernails. Three layers of keratin form every hair. The outer sheath of cuticle forms overlapping scales.

Hair proteins have a high sulfur content from the amino acid cysteine which can easily form cross-links to other cystines in the hair molecule. These bonds are responsible for the hair's toughness and abrasion resistance and the cross-links hold the hair fibers together. As long as this organization is not disrupted, the fiber is strong and appears "healthy". The breaking and re-linking of cysteines in the hair protein is used to "perm" the hair to change its shape and add curl to the hair.

Chemicals applied to hair and mechanical flexing of hair can sometimes damage the structure of these biologic filaments and cause the hair to have an undesirable appearance, be less manageable, or be more vulnerable to breakage.

Hair Length and Growth

Hair grows at a faster rate in the spring and summer than in autumn and winter - a fact that often is used to "prove" that certain hair growth remedies stimulate hair growth. The growth rate is however very much related to the individual person, his age, diet etc. The lifetime of the anagen phase is responsible for the maximum of hair length you can have. Waist length hair takes about 5 years to grow out from a short hair cut, periodic trims included. If your hair has a lifecycle of 2 years, you will never achieve a nice waist length mane. In rare families, long hair cycles are combined with rapid hair growth - producing floor length hair in women. At right is the person with the longest well documented record for hair length who is Diane Witt, a mother of two who lives in Worcester, MA. Her hair measured over 12 ft. 8 in. in March 1993. Witt has not measured (or cut) her hair since then.

Hair Color: Blonde, Red, Brown, and Black

The hair roots or follicles contain pigment cells that, depending on your genetic background, creates a black pigment called melanin or eumelanin and a reddish pigment, produced by a separate gene, called heomelanin (or sometimes called phaeomelanin). The greater the amount of pigment sent to the hair, the darker the hair becomes. if the amount of pigment is reduced, the hair color turns brown and then reddish or blond. Color changes with age. Most "towheaded children" who have blonde-whitish hair turn into brunet adults.

The shades of hair color are influenced by how light bounces off the hair proteins, but basically depends upon pigment contained within the hair shaft center or cortex. Eumelanin is the pigment found in brown or black hair and to lesser degrees in blonde hair. Heomelanin, produces red hair while and mix of eumelanin and heomelanin produces a blonde-red mixture or "strawberry blonde". When pigment is significantly diminished, the hair appears gray and when it is absent, the hair is white.

Under severe stress hair or malnutrition, hair can lose its color. In the trench warfare of World War I, there were cases of young men whose hair turned gray within two months after prolonged episodes of severe fighting and artillery bombardments. Copper is the key nutrient in pigment (melanin) production in the skin and hair. A lack of sufficient dietary copper can cause hair to lose its color.

Hair Biology and Care

Hair Follicles as the Source of Hair

The Structure of Hair

Care of Hair Fibers

Secrets of Growing Long Hair

The Functions of Head and Facial Hair

Hair Procedures and Recovery

The Truth about Hair Relaxers