Wherein I spake of most disastrous chances,
Of moving accidents by flood and field,
Of hair-breadth ’scapes i’ the imminent deadly breach.

Today we know that it takes not 48 but more like 300-400 average-diameter hairs, laid side by side, to make one linear inch. Moreover, we are aware that the diameter of all adult human hairs will vary according to the nationality, color, age, and sex of the individual, as well as the locality from which the specimen is taken.

Except for the hair on the scalp, eyebrows and eyelashes, the hairs on young people up to the age of six or seven are so fine, short, and colorless, they are near invisible. These vellus hairs, which succeed the even tinier (lanugo) hairs that cover most of the body at birth, remain the same small diameter throughout childhood, about .0381 mm to .0432 mm.

The fine vellus hairs in the armpits and on the pubes are replaced by progressively coarser terminal hairs during adolescence. Over a several-year period, less pronounced changes appear on the chest, abdomen, arms, legs, and other parts of the body. The coarsening of hair is more pronounced in males, particularly in the beard and moustache areas. The chemical composition of hairs is similar in all persons, but the diameter and contour of hairs varies greatly.

Through genetic inheritance, Chinese beard and scalp hairs are coarser than those of Caucasian or Negro origins. The hair of New Zealand’s Maori people is coarser than that of South American Indians. In turn the hair of Indians is coarser than that of Europeans. The diameter of Maori hairs will vary between .056 mm and .127 mm, depending on what part of the anatomy they are taken from; the hairs of Indians will measure between .0560 mm and .0847 mm; and those of the Europeans will be from .0462 mm to .0635 mm. The average diameter of all the hairs when taken together is close to .0635 mm (or 1/400 of an inch).

To give a better idea of size; it would take around 158 of the average-size hairs, laid side by side, to measure one linear centimeter. Nevertheless, when taken in the aggregate, the amount of surface area that these superfine filaments can cover is quite incredible. For instance there are about 100,000 strands of hair on the human scalp. If we were to cut a foot-long hank of this hair from every citizen of New York, and lay each strand down on the ground, one immediately alongside the other, we would have a footpath of hair 47,624 km in length. That’s long enough to belt the earth at the equator – and have enough left over to carpet every sidewalk in Boston!

Common opinion to the contrary, the hair of men is generally finer than that of women of the same nationality by as much as .0169 mm. Some of the first in-depth studies relating to the variances in hair-shaft sizes of hairs from different body locations on different types of people, were conducted by English physician, Dr. Erasmus Wilson, around 1876. Dr. Wilson (who became mildly famous for moving a Cleopatra’s Needle from the banks of the Nile, in Egypt, and setting it up back home on the banks of the Thames), carefully examined 2,000 hairs removed from the scalps of 18 men and 18 women. Among other things, it was found that even on the same head there is a great difference in the size of the hair shafts.

From Dr. Wilson’s observations it was ascertained that flaxen hairs are the finest, having an average diameter of .0553 mm (1/460 inch); slightly coarser are red hairs, averaging about .0600 mm (1/424) in diameter; third are dark brown hairs, about .0678 (1/375 inch); black hairs are fourth, averaging around .0681 mm (1/373). In fifth place is light brown hair, which contains the broadest range of fine to very coarse hairs. The average of which is .0760 mm (1/334 inch) in diameter.