1. Definition
Hair loss, or clinically known as alopecia, is the thinning of hair on the scalp. Alopecia can be temporary or permanent. It occurs gradually with age in both men and women, but usually more pronounced in men.
There are three phases to a hair cycle: anagen, catagen and telogen. Anagen is described as the growing phase, whereas cell division occurs. These hairs have long, indented roots covered with intact inner and outer root sheaths, and they are fully pigmented.
At the base of the follicle, the amount of pigment decreases to form a keratinized layer surrounding the hair. Here, the hair enters the transitional phase, catagen. Cell division reduces and hair starts to grow upward. Telogen is the resting phase of the hair, in which hair stops growing and rooted by a club-shaped root in the follicle.
When the anagen phase starts again, it forces the roots of the old hair to be removed and the cycle repeats. The characteristic of the hair cycle is not synchronous across every single hair strand, but varies between the site of the head and the age of patients. In the scalp, for example, the average length of the anagen phase is 1000 days; the catagen phase lasts only a few days; and the telogen phase lasts 100 days.
Normal adults have 100,000 – 150,000 hair strand of average, and 90% of them are in anagen (growing) phase at any given time. While it is normal to experience loss of up to 100 hair strands per day, any number higher than that is considered clinical hairloss.
Hair loss can be categorized by the stage in which it occurs.
– Telogen effluvium is defined as the early and excessive loss of hair, usually caused by trauma or stress factors that speeds up the cycle. The result is when a new cycle begins early, it pushes the old club hair out, causing thinning of the scalp hair.
– Anagen effluvium is caused by damages to the dividing process of the cell. It is normally a side effects of chemotherapy or an underlying disease, such as thyroid diseases, atopic dermatitis or psychiatric disorders.
2. Epidemiology
The prevalence of the condition is dependent on the patterns of alopecia.
Most common pattern occurs in men and women are androgenetic alopecia, caused by genetic and hormone imbalance. The condition increases in prevalence with age, affecting almost half of the men over 50 and approximately a third of Caucasian women over 70. The variation in ethnicity is significant, with men and women of Oriental origin have less chance of getting the pattern.
Alopecia areata, an autoimmune disease that cause the immune system to attack the body’s hair follicle, is the second most common pattern. It is most common between the age of 15 and 29, affecting approximately 15 per 10,000 of the population in the UK.
3. Causes & risk factors
Each types of alopecia have different causes, some are more well-understood than others. The most common causes of hair loss are:
– Genetics
– Immune system imbalances, caused by autoimmune diseases such as hyperthyroidism or diabetes. Patients with Down syndrome are also reported to be susceptible to alopecia areata
– Chemotherapy
– Intense emotional or physical stress
– A long term illness, such as cancer or liver disease
– A sudden change in diet
– Certain medications, such as beta-blockers or anti-coagulants
Sources:
http://www.nhs.uk/Conditions/Hair-loss/Pages/Introduction.aspx
http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/definition/con-20027666
https://www.nlm.nih.gov/medlineplus/ency/article/003246.htm