Average Human Hair Diameter

The average human hair diameter is 99 um. A single um is equal to one millionth of a meter. It is also equivalent to one thousandth of a millimeter (0.001 mm). In inches, the diameter would be 0.001. In centimeters it would be 0.00254.


Human hair is protein filament which grows from the follicles in the skin. Hair can grow in many parts of the human body except the palms, the soles and lips. Hair is mostly concentrated in the following areas: the top of the head, the pubic area, armpits, legs, eyelashes, eyebrows, ears, nose and legs.


Human hair is divided into three areas: the bulb, the root and the shaft. The bulb is the swelling portion at the base of the hair. The root is the part of the hair which is under the surface. The part over the surface is the shaft.

There are three components in cross-section: the medulla, cortex and cuticle. The medulla is the part at the core which contains airspaces and loose cells. The cortex holds keratin while the cuticle is made of cells assembled like shingles on a roof.


No matter what the average human hair diameter is, human scalp will typically grow at 0.4 mm daily. Human scalp growth is four times quicker compared to human nails. This assumes that the human body is in good condition. Health issues can slow the growth of hair.

Facts and Trivia

On the average, a human head has 100,000 hairs. According to some studies, blonds have on average 140,000 hairs, brunettes 110,000 and redheads 90,000. The hair grows at an annual rate of 12 centimeters. Hair can grow to a maximum length of 90 cm.

Male hair is denser compared to females. Each hair has an average lifespan of 2 to 7 years. Weather affects hair; humidity will stretch it. There is also evidence that warm weather promotes faster hair growth. As people get older, hair loses its density and growth slows.

Hair Color

The color of the hair, skin and eyes are all determined by genetics. Cells known as melanocytes are responsible for passing these traits. They produce the pigments that make hair color. The mixture determines whether you have blond, red or black hair.

The average human hair diameter is just that, an average. Some people grow more hair, and in others they grow more slowly. Several factors can affect it such as genetics.

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