The hair is made up of two structures:
what’s visible above the scalp and what is not visible beneath it (the follicle). The follicle produces the protein called keratin, which makes up all hair. As old keratin cells die and new ones are produced, the dead cells are strung together and pushed through your scalp, creating the visible hair that you grow, cut, and style.
The cycle of hair growth consists of three distinct stages
anagen, catagen, and telogen. Any individual hair strand may be in a different hair growth stage at any time. Hair loss usually occurs when one or more of these phases is disrupted by another condition.
- During the anagen stage – the active hair growth phase – the hair cells are dividing quickly and regularly. This phase lasts from 2 to 7 years. Once the hair has stopped growing, it transitions into the next phase.
- The catagen stage is a transitional stage, lasting for about 2 to 3 weeks where growth stops and hair detaches from the root, moving outward toward the scalp.
- The telogen stage is the resting phase, lasting for approximately 2 to 4 months, where the hair sheds to allow hair regrowth to begin.
There are a number of ways people can lose their hair. The most common types of hair loss are:
Involutional alopecia, a natural condition that causes the hair to gradually thin as you age. This causes a greater number of hair follicles to go into the resting (telogen) phase, while the remaining hairs become shorter and fewer in number.
Androgenic alopecia, a genetic hair loss condition that can affect both men and women.
Men can experience androgenic alopecia (also known as “male pattern baldness”) as early as their teens or early 20s. Men with this condition may notice a receding hairline and gradually thinning hair around the crown of the head and the front of the scalp.
Alternatively, women can experience “female pattern baldness” which shows no noticeable thinning until at least age 40. It’s common for women to begin losing hair across the entire scalp, most extensively at the crown.
Alopecia areata is most common in children and adolescents. This condition may cause you to experience sudden hair loss. It may result in patchy hair loss, complete baldness (alopecia totalis) or total body hair loss, including eyebrows and eyelashes (alopecia universalis). The large majority of people with alopecia areata regrow hair within a few years.
Trichotillomania (hair-pulling disorder) is a psychological, self-inflicted condition in which you repetitively pull out your own hair. This condition is most commonly diagnosed in children.
Telogen effluvium is a temporary bout of thinning hair which occurs due to changes in the growth cycle of hair. When a large number of hairs enter the resting (telogen) hair growth phase at the same time, you can experience excess shedding and thinning.
Scarring alopecia is a type of alopecia that results in permanent hair loss. Inflammatory skin conditions – such as folliculitis, acne, and other various skin disorders – often result in scar tissue that destroys the hair follicles and, thus, the ability of the hair to regrow.
Traction alopecia is a type of gradual hair loss that is caused by constant pulling or tension of the hair that can create inflammation and eventually scarring, which can prevent future hair growth.