BEARD

Hair is a flexible thin keratin thread with great strength and elasticity. It is present on almost all surfaces of the human skin. The hair shaft has three major parts the cuticle, cortex, and medulla. The hair growth cycle has three-phase i.e. Anagen phase (growth phase), Catagen phase(lower follicle), Telogen phase (a period of rest and recovery )

Hair is classified based on shape, size, and color. Three major hair follicle types can be differentiated, including lanugo hair, vellus hair, and terminal hair.

• Lanugo hair – Very fine & soft hair. Mostly shed at birth and is replaced by vellus hair.
• Vellus hair – Short, soft, colorless hair fibers
• Terminal hairs – Located on the scalp face, chest (mainly for men) arm and legs, etc. varies with the body location and function.

Some hair follicles have the ability to move from one category to another at various times. Males have a beard during puberty which produces only vellus hairs and is capable of producing terminal hair thereafter.

Androgens stimulate more visible body hair during puberty (e.g., beard) and continue increasing various hair follicle and hair sizes for many years

Having a beard is Unhygienic?
No, beards are not unhygienic because human skin including the face has a lot of bacteria, and many are not harmful. A study was conducted on men having beards and without beards they found men having facial hair were less likely to be colonized with Staphylococcus aureus. Clean shaved men had 10% more Staphylococcus aureus bacteria on their faces when compared to beard men.

Why some men can’t grow beard?
Many men have a genetic problem. Androgens have the ability to grow facial hair. An enzyme is responsible in your body called 5-alpha reductase which converts the androgen hormone testosterone into another hormone called dihydrotestosterone (DHT). DHT binds to receptors on your hair follicles and stimulates the growth of facial hair. However, the strength of its effect is also determined by your hair follicles’ sensitivity to DHT. This sensitivity is largely determined by your genetics.
There is some reduction in the total number of hairs on the scalp with an increase in age, the most noticeable changes in hair patterns with an increase in age occur due to hair follicle miniaturization as a result of androgenetic alopecia, rather than hair follicle depletion due to senescence.
Certain class or group of people has less facial hair growth.
Few people suffer from Alopecia areata in this situation facial and head hair follicles are suffered and this causes hair loss. Few people may suffer from low testosterone levels also.

Why do men go bald, but still have facial hair (beards)?
Hair that grows on the face, usually chin, cheeks & upper lips region (i.e Beard & Mustache). It is typically a secondary sex characteristic of human males. The growth of this hair is hormone-driven or also called androgenic hair. Hormones responsible for the full growth of facial hair are testosterone & DHEA. The Growth of Androgenic hair is related to the level of androgen & density of androgen receptors in dermal papillae, both must reach the threshold for the proliferation of hair follicles. A decrease in the level of the hormone leads to a patchy beard or less beard volume.

Scalp hair referred to as hair on the head, grows without any hormonal factor. It basically works on different phases of the hair cycle i.e anagen and telogen ratio.

Irrespective of facial hair DHT plays an opposite role on scalp hair, it is the reason behind male pattern baldness and hair fall in male post-puberty.

 Women produce less testosterone than men and generally don't develop much facial hair. But both sexes are sensitive to testosterone in particular areas. Men and women both have underarm and pubic hair. While testosterone stimulates hair growth, it is genetics that determines how thick and dark hair will be. So if you are a man and go bald or can't grow a goatee, it's your family tree, not the hormone levels.

The average full-headed person has on the order of 100,000 scalp hairs. People lose up to 100 hairs a day, as evidenced by your comb or brush. Human hair occurs everywhere on the body, except for the soles of the feet, the palms of the hands, the lips, and the eyelids, apart from eyelashes. A person's hair has its own cycle of growth. Generally, hair grows for a few years, rests for a few months, sheds and new hair grows. The rate or speed of hair growth is about 0.5 inches per month or about 6 inches per year.

References:
1. FASEB Journal
2. Index Journal