What’s the construction of hair and the way does it develop?

For many individuals, hair is a pure a part of their look and an expression of their persona. Hair may provide safety: As an example, it helps to maintain the solar’s rays from reaching our scalp. Eyelashes and eyebrows hold mud, grime and sweat out of our eyes. Even the hairs in our nostril and ears assist to maintain out germs and different overseas objects. Physique hair helps to manage our physique temperature: The hairs arise when it’s chilly, holding the air that’s warmed by the physique near the physique – like a warming layer of air.

Various kinds of hair

Apart from a number of locations, just like the palms of our arms or the soles of our toes, the whole floor of our physique has hair on it. The 2 most important sorts of hair are the shorter and thinner “vellus” hairs (peach fuzz) discovered on the physique and the longer and thicker “terminal” hairs. Examples of terminal hairs embody the hair in your head, facial hair, eyelashes, eyebrows, pubic hair, chest hair and stomach hair.

How a lot of every hair sort you have got varies from individual to individual and in addition is dependent upon your age and intercourse. Kids’s our bodies largely have vellus hair, for example. About 30 p.c of the physique’s floor is roofed with terminal hair in girls, in comparison with about 90 p.c in males.

Hair construction

Every hair has a hair shaft and a hair root. The shaft is the seen a part of the hair that stands proud of the pores and skin. The hair root is within the pores and skin and extends right down to the deeper layers of the pores and skin. It’s surrounded by the hair follicle (a sheath of pores and skin and connective tissue), which can be related to a sebaceous gland.

Every hair follicle is hooked up to a tiny muscle (arrector pili) that may make the hair arise. Many nerves finish on the hair follicle too. These nerves sense hair motion and are delicate to even the slightest draft.

On the base of the hair, the hair root widens to a spherical hair bulb. The hair papilla, which provides the hair root with blood, is discovered inside the underside of the hair bulb. New hair cells are consistently being made within the hair bulb, near the papilla.

Illustration: Structure of a hair – as described in the article

How does hair develop?

New cells are consistently forming within the hair bulb. These cells stick collectively and harden. The complete strand of hair develops from this group of hardened hair cells. As a result of new hardened cells carry on attaching to the hair from under, it’s step by step pushed up out of the pores and skin. On this approach, a single hair in your head grows at a charge of about 1 cm per thirty days. Facial hair, and particularly eyelashes, eyebrows and physique hair grows at a slower tempo.

Whether or not it’s straight or curly will depend upon the cross-sectional form of hair. Spherical hair grows straight out of the pores and skin. The extra oval-shaped the cross-section is, the curlier the hair can be.

The colour of the hair is decided by the quantity of melanin within the hardened cells. This may differ quite a bit from individual to individual, and it modifications over the course of a lifetime. The quantity of melanin sometimes decreases as individuals become older, and extra air will get trapped contained in the hair – it then loses its shade and turns white. Relying on somebody’s authentic hair shade and the variety of white hairs that develop, the hair on their head then turns grey or white.

Hair development cycle

So long as new hair cells proceed to develop within the hair bulb, the hair continues to develop longer. This development part can be known as the anagen part. At any time limit, about 90 p.c of an individual’s whole quantity of hair is on this development part.

Relying on the place on the physique a hair grows, the expansion part will last more or shorter: As an example, the expansion part of hair in your head can final a number of years,, so it will probably develop to over a meter in size if you do not have it reduce. The expansion part is particularly quick for eyelashes, eyebrows, nasal hair and ear hair. These hairs solely develop for about 100 to 150 days, to allow them to’t get that lengthy.

On the finish of the expansion part, the hair root separates from the papilla. Then a transitional part known as the catagen part begins, lasting about two to 4 weeks. When the hair has separated utterly from the papilla, the availability of blood is reduce off within the last resting part, which can be known as the telogen part. The hair is step by step pushed out of the pores and skin and finally falls out. The resting part can final a number of months.

New hair cells then begin to multiply on the base of the “empty” hair follicle to type a brand new hair, and the expansion part of the hair development cycle begins once more.

What causes elevated hair loss?

As a result of hairs proceed to enter the resting part after which fall out, we’re consistently dropping hair. A wholesome grownup could lose about 70 to 100 hairs on their head per day. However as a result of new hairs are all the time rising and changing them, this pure hair loss is not noticeable.

The speed of hair loss could enhance noticeably if the hair roots are broken through the development part or if plenty of hairs go into the resting part on the similar time. If no new hair grows and replaces the hair, that a part of the pores and skin turns into bald. This kind of hair loss is known as alopecia – no matter how massive the bald spot is or whether or not it impacts the scalp or physique hair. In some sorts of alopecia, the hair could develop again. However baldness can be everlasting – one typical instance is gradual hair loss in males (male sample hair loss).


  • Lippert H. Lehrbuch Anatomie. Munich: City und Fischer; 2017.

  • Menche N (Ed). Biologie Anatomie Physiologie. Munich: City und Fischer; 2016.

  • Pschyrembel. Klinisches Wörterbuch. Berlin: De Gruyter; 2017.

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