Hair Science

Hair is genuinely individual and cannot be summed up in a few facts & figures. That said, vital statistics can sometimes be useful. However, since every hair and head of hair is absolutely unique, the figures on this page are of course only averages.
  
Hair is the fastest growing tissue in the body, second only to bone marrow.

The diameter of an average single hair is 58 to 100 microns. However, since the cross section of a hair is elliptical, the term diameter is not totally accurate. A micron is one millionth of a meter, or one thousandth of a millimeter - it therefore takes 10 to 20 hairs "piled up" together to obtain a thickness of one millimeter.

The average number of hairs per square centimeter of scalp is 250. This figure varies between 200 and 300 according to the area of scalp in question as also the thickness of the hair.

The total surface area of an average head of hair 20 centimeters long would be 6 meters squared. This is an important figure, as when shampooing for example, this is the surface that must be washed. Since the surface area of the scalp is 600 cm², a head of hair 20 centimeters long therefore occupies an area 100 times greater than its place of origin.

The average speed at which hair grows is 1cm per month. This corresponds to a daily growth rate in excess of 0.3 mm per day and an annual growth of 12 centimeters per hair. By applying these figures to the entire head of hair, we see that it is produced at the rate of more than a 36 meters a day, some 1.1 kilometers per month, or more than 13 kilometers a year! In terms of weight, for the entire head of hair this represents 0.2 grams per day, 6 grams a month or 72 grams year. Since hair grows from its roots, the tip of a hair 12 cm long will be one year old. But as a single hair has on average a three-year growth cycle, it is rare to see hair longer than one meter, which represents over eight years of growth However, the world record for hair length stands at 4.2 meters. If this hair had grown at a normal rate, its tips would be 35 years old!

The average weight of a head of hair according to the length of the hair making it up is 5 to 200 grams. 30% of its own weight, the percentage of weight in water that a hair in good condition can absorb. If it has been weakened, this percentage can reach 45%

90% of scalp hairs are growing and 10% are resting at any one time.
 
It is normal to lose 100 hairs per day from the scalp and you can lose over 50% of your scalp hairs before it is apparent to anyone.
 
Many drugs can cause hair loss.
 
Thyroid imbalance and iron deficiency are reversible causes of hair loss.
 
Over 50% of men by age 50 have male pattern hair loss.
 
Forty percent of women by the time they reach menopause will have female pattern (hereditary) hair loss.
 
There are 100,000 hairs on the average adult head with blondes having most (120,000) and redheads least (80,000)
 
Hair grows faster in the summer, during sleep and between the ages of 16 and 24
 
Between the ages of 40 and 50 women tend to lose about 20 percent of their hair
 
Healthy hair is highly elastic and can stretch 20 or 30 percent before snapping
 
A human hair is stronger than copper wire of the same thickness & the combined strength of a head of human hair is capable of supporting the weight equivalent of 99 people