On average, humans have up to 150,000 hairs on their head and five million over our bodies. From our eyebrows and beards to tiny hairs in our noses and ears, they all grow in the same way. Each of these individual hairs has gone through four growth phases:
We lose an average of 50 to 200 hairs per day for normal, healthy adults although this can vary depending on factors such as health, diet, medications, genetics, aging, or other factors.
Each phase of hair growth is part of an important cycle that repeats as hair grows and eventually falls out (sheds). Hair growth begins beneath the surface of the skin as a follicle where the root is made up of protein. The bulb of the hair shaft receives blood supply and hormones and begins to grow through the pores of the skin and scalp.
Interestingly, on a microscopic level, there are different shapes of follicles that determine whether hair is curly, wavy, or straight and these shapes can change over time.
In the simplest terms, our hair-growth cycle is one of growth, death, and regrowth but each phase is more complex than this and each phase is a crucial part of having a healthy head of hair.
The Anagen Phase
During the anagen phase, hair is actively growing. The average rate of hair growth is .5 inches per month and the anagen phase lasts anywhere from four to six years, depending on the individual. For body hair, the anagen phase is believed to be much shorter.
The hair follicle is fed nutrients from the blood vessels in the scalp and begins to grow. As it grows, it passes by an oil gland in the pore before getting pushed up through the surface of the skin, although once past the skin, the hair shaft is actually dead (which is why it does not hurt to cut hair).
For men and women who experience Androgenic Alopecia, a hormone called Dihydrotestosterone (DHT) shortens the length of the anagen phase resulting in thinner hair for women and receding hairlines and crown thinning for men (what is commonly referred to as male pattern baldness).
The Anagen phase can be shortened by factors such as stress, diet, aging, or other conditions varying from person to person.
The Catagen Phase
After the Anagen phase ceases, the catagen phase begins. During the catagen phase, each hair detaches from the blood vessels under the skin and stops growing. The hair begins to die because of the lack of blood and oxygen from the blood vessels. The Catagen phase lasts for approximately two weeks.
The Telogen Phase
During the Telogen phase, hair is simply resting in the scalp. This phase lasts for approximately 100 days for hair on the scalp but considerably longer for other body hair.
Telogen Effluvium is caused when a shock to the system such as childbirth, crash dieting, severe stress or other shock causes the hair to shed for excessive amounts of time resulting in thinner hair. It's more common in women than men and is usually reversible.
The Exogen Phase
This phase is an extension of the Telogen phase where the hair follicle is shed and new hair simultaneously begins to grow, beginning a new anagen phase. From here, the cycle repeats.
Not every hair is always in the same stage of growth which is why we don't all experience baldness every few years. Depending on your diet, medications, health, age, gender, and other important factors, any one of these phases can be either enhanced or disturbed and if you are experiencing any kind of hair loss, the best way to determine what is causing it is to speak with a professional.
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