3 Main Phases of the Hair Cycle
1) Anagen- actively growing hair; most hair is in this stage (hair length depends on the duration of anagen)
2) Catagen- in between phase that lasts 2-3 weeks where the hair growth stops and the follicle shrinks; ~ 1-3% of hair is in this stage
3) Telogen- resting phase that lasts for 1-4 months; ~ 10% of hair is in this stage
Anagen Effluvium occurs when hairs are shed during the anagen stage. This occurs suddenly and will present as short broken off hairs or slightly tapered.
Common causes of Anagen Effluvium
· Autoimmune processes
· Medications such as cytotoxic/chemo drugs (if medication is removed hair growth can return to normal within 3-6 months)
· Loose/Short Anagen Syndrome- will present typically during childhood; child will present with normal hair growth; however, the hair will not grow past a certain length and remains short
· Radiation treatments
Telogen Effluvium happens approximately 2-6 months after an event that causes active hair growth to stop. The telogen hair has a bulb at the end known as club hair.
Common causes of Telogen Effluvium
- Recent pregnancy/breast feeding
- Surgical Procedures
- Acute Blood loss
- Traumatic events
- Psychological stress
- Nutritional and Iron Panel
Androgenic Alopecia in Men (Male patterned hair loss)
· Physiologic reaction induced by androgens in genetically predisposed men.
o 2 types of scalp follicles- 1) Androgen sensitive follicles on the top of the scalp. 2) Androgen independent follicles on the sides and the back of the scalp
o So under the influence of androgens, the androgen sensitive follicles gradually miniaturize and hair density decreases.
· Thinning of hair begins between 12-40 yoa; half the population expresses this trait before 50 yoa
· Triangular frontotemporal recession happens in most men and women after puberty; however first signs of balding are noted with increased frontotemporal recession and midfrontal recession. Followed by hair loss on the vertex. The density of the hair decreases over the top of the scalp.
Androgenic Alopecia in Women (Female patterned hair loss)
· Affects 40% of women by the age of 50
· Typically presents with thinning on the top and crown of the scalp. Usually begins with widening of the central hair part. Pt usually retains the normal hairline without frontotemporal recession
· Androgenic Alopeciea (AGA) is a condition affecting men AND women. Although the exact cause is unknown, it is believed to be related to a genetic sensitivity to DHT (dihydrotestosterone). In an affected person, the hair follicles of the scalp are sensitive to DHT, and binding of this hormone to the follicle causes shrinking or miniaturization. Over time, this shortens the follicles lifespan and the ability to grow hair.
· Although the process is the same in men and women, the pattern of hair loss is very different. Men tend to have thinning and erosion of the vertices of the scalp first which then extends to the vertex/crown and eventually the entire superior aspect of the scalp. Women tend to maintain their hairline, but become very thin in the frontal and vertex/crown area. The scale for grading loss in men and women is known as the Norwood/Hamilton scale