Hair Anatomy





Shabby Apple



Hair Anatomy.....A hair grows from a follicle extending from the dermis into the epidermis. It is a derivative of the epithelium.


Hair Structure and Follicles


There are three recognizable zones along the length of this body structure:

Bulb – consists of epithelial cells and is a swelling at the base where the hair originates in the dermis. The epithelium at the base of the bulb surrounds a small hair papilla, which is composed of a small amount of connective tissue containing tiny blood vessels and nerves.

Root – is the hair within the follicle internal to the skin surface.

Shaft – is that part that extends beyond the skin surface.

The root and the shaft are made up of dead epithelial cells. On the other hand, the hair bulb contains living epithelial cells. That is why it doesn’t hurt to have your hair cut because your hairstylist is cutting dead cells. However, if you pull one out by its roots you feel pain, because you are disturbing the live portion of it.

Production of this structure involves a specialized type of keratinization that occurs in the matrix, which is inside the bulb. Basal epithelial cells near the center of the matrix divide. This produces daughter cells that are gradually pushed toward the surface. The medulla, not found in all hair types, is a remnant of the soft core of the matrix. It’s composed of loosely arranged cells and air spaces, and contains flexible, soft keratin. The relatively hard cortex is formed by several layers of flattened cells closer to the outer surface of the developing hair. Stiffness is derived from the hard keratin contained within the cortex. Multiple cell layers around the cortex form the cuticle, which is the coating. The free edges of cuticle cells are directed externally.

Skin Section Through a Hair Shaft and Follicle
Skin Section Through a Hair Shaft and Follicle

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Cunningham, John...
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The follicle is an oblique tube that surrounds the root hair. The follicle always extends into the dermis and sometimes into the subcutaneous layer. There are two principal concentric layers of the cells of the follicle walls. There is an outer connective tissue root sheath, which originates from the dermis. There is also an inner epithelial tissue root sheath, which originates from the epidermis.

There are also two parts to the epithelial tissue root sheath: an internal root sheath and an external root sheath. Peripheral cells of the matrix produce the internal root sheath. This layer of cells is destroyed quickly so it doesn’t extend the full length of the follicle. The external root sheath generally contains the same epidermal cells as the skin surface and extends between the skin surface and the hair matrix. However, all of the cells resemble those of the stratum basale where this sheath joins the hair matrix.

There are thin ribbons of smooth muscle, collectively known as the arrector pili muscle, that extend from the dermal papillae. Emotional states such as rage or fear, or exposure to cold temperatures stimulates the arrector pili, pulling on the follicles and elevating the hairs. Thus, “goose bumps” are produced.

Columnar Epithelium X400 Hair Follicle Photomic
Columnar Epithelium X400 Hair Follicle Photomic

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Hair Type and Distribution


Hair anatomy.....Another name for a single hair is a pilus. Its shape is a slender filament, and is composed of keratinized cells growing from follicles that extend deep into the dermis. They often project into the underlying subcutaneous layer. Texture and pigmentation causes the primary differences in hair density.

There are three types produced during your life. These three kinds are called lanugo, vellus, and terminal.

Lanugo – This is the fine, unpigmented , downy kind that first appears on the fetus in the last trimester of development.

Vellus – This is a similarly fine, unpigmented or lightly pigmented ind that replaces the lanugo at birth.

Terminal – This is usually a coarser, pigmented, and longer kind than the vellus. It grows on the scalp, comprises the eyelashes and eyebrows. At puberty, terminal replaces vellus in the axillary, or underarm area, and the pubic regions. The beard that forms on males is also terminal, as well as on the male arms, legs, and trunk.

Little Irene, Portrait of the 8 Year-Old Daughter of the Banker Cahen D'Anvers, 1880
Little Irene, Portrait of the 8 Year-Old Daughter of the Banker Cahen D'Anvers, 1880

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Renoir,...
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Hair Color


The synthesis of melanin in the matrix adjacent to the papillae results in hair color. Genetically determined differences in the structure of the melanin are what cause the different variations in color. Other factors that influence color are environmental factors and hormonal factors. Pigment production decreases as you age. This results in lighter color. When there is gradual reduction in melanin production with the follicle, gray hair is the result. No pigment at all results in white color. Usually, color changes gradually.

Lady with Short Dark Hair Wearing a Skimpy Dress in White Silk or Satin
Lady with Short Dark Hair Wearing a Skimpy Dress in White Silk or Satin

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Serveau, Clement
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Function of Hair


There are millions of hairs on the surface of your body. They have important functions.

Protection – The scalp in protected from injury and sunburn by the ones on your head. The ones within the nostrils protect the respiratory system by preventing inhalation of large foreign particles. The external ear canal is protected from insects and foreign particles by the ones that are there. Eyelashes and eyebrows protect the eyes. The lashes protect the eye from particles and the brows from sweat running down the forehead.

Facial Expression – The eyebrows also function to enhance facial expression.

Heat retention - The ones on the head helps to prevent the loss of conducted heat from the scalp into the surrounding air. People with a full head of hair lose far less heat then those who have lost theirs. The only place where it is thick enough to retain heat is on the scalp.

Visual identification – Hair characteristics are important in determining species, age, and sex as well as identifying individuals.

Sensory reception - They have associated touch receptors or root plexuses that detect light touch.

Chemical signal dispersal – They help disperse pheromones, which are chemical signals involved in attraction of the opposite sex and in sex recognition. After pheromones are secreted by selected sweat glands, such as those in the axillary and pubic regions, they are released onto the hairs in these regions.

Girl with Long Hair
Girl with Long Hair

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Hair Growth


Hair anatomy .....One hair on the scalp normally grows about 1/3 of a millimeter or 13/1000 of an inch per day, for two to five years and may reach a length of about a meter or 3 and 1/4 feet. After this growth phase it normally enters a dormant phase of three to four months. A new one begins to grow inside the follicle internal to the older one. The new one eventually pushes out the old and it falls from the follicle.

The scalp normally loses about 10 to 100 per day, though the growth rate and duration of the growth cycle will vary. If a health problem exists it can cause continuous losses of more than 100 a day. Temporary losses may be caused by:

• Drugs
• Dietary factors
• High fever
• Radiation
• Stress


Alopecia is a thinning of the hair and can be caused by:

• Aging
• Drugs


Old Woman at Prayer
Old Woman at Prayer

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It can occur in either sexes.

Diffuse hair loss is a condition that is both dramatic and distressing. It's loss from all parts of the scalp. This condition is primarily seen is women and can be caused by:

• Drugs
• Hormones
• Iron deficiency


Male pattern baldness is a condition in males causing loss of hair first from only the crown region of the scalp rather than uniformly. It’s caused by a combination of genetic and hormonal influences. At puberty the testes begin secreting large amounts of male sex hormones, primarily testosterone.

As one effect of sex hormone production, males develop a typical pattern of underarm, facial, and chest hair. The relevant gene for male pattern baldness has two alleles, one for uniform hair growth and one for baldness. The baldness allele is dominant in males and is expressed only in the presence of a high level of testosterone.

In men who are either heterozygous or homozygous for the baldness allele, testosterone causes the terminal kind of the scalp to be replaced by thinner vellus, beginning on the top of the head and later on the sides.

The baldness allele is recessive in females.

This is a sex-influenced trait in which an allele is dominant in one sex and recessive in the other. Changes in the level of sex hormones found circulation in the blood can affect development on the scalp, causing a shift from terminal to vellus production.

Rexall, Hair Shampoo Tonic, USA, 1910
Rexall, Hair Shampoo Tonic, USA, 1910

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