An average person’s scalp contains 250,000‒500,000 hair follicles. Each follicle undergoes repeated cycles of three phases (Santos 2015):
- anagen, the growth phase, during which hair elongates;
- catagen, the regression phase, during which the follicle shrinks and detaches from its hair; and
- telogen, the resting phase.
On a healthy scalp, about 90–95% of hair follicles are in the anagen phase at any given time (Qi 2014; Santos 2015). Under normal circumstances, scalp hair shedding of 50‒150 hairs per day is matched by new hair growth at the same rate, so there is no net loss or gain (Fiuraskova 2003; Ahanogbe 2015).
Cells at the base of the hair follicle, in a region called the dermal papilla, are responsible for initiating and regulating the hair follicle cycle (Driskell 2011). These dermal papilla cells are regulated by hormones, growth factors, and inflammatory cytokines (Santos 2015; Inui 2013).
Types of Hair Loss
Androgenetic alopecia, also called male and female “pattern” hair loss, is the most common type of alopecia in men and women. Male pattern hair loss typically causes thinning and recession along the front hairline and temples, as well as the crown of the head. Female pattern hair loss usually causes thinning at the crown of the head (Qi 2014).
Male pattern hair loss is triggered mainly by the effects of the androgen (male hormone) dihydrotestosterone (DHT) on the dermal papilla cells of the hair follicle. DHT is made from testosterone by the enzyme 5-alpha reductase. DHT shortens the anagen phase in genetically predisposed hair follicles, resulting in smaller and shorter hairs (Fiuraskova 2003; Qi 2014). Female pattern baldness may involve a follicular sensitivity to DHT (Herskovitz 2013); however, the drop in estrogen after menopause may also contribute to changes in hair follicles that result in increased hair loss (Levy 2013).
Other types of alopecia include (Qi 2014; Hawit 2008; Mayo Clinic 2015):
- Alopecia areata. Alopecia areata, an autoimmune condition in which the immune system attacks hair follicles, can affect children and adults of both genders. It causes round patches of balding, mostly on the scalp and beard region.
- Telogen effluvium. Telogen effluvium is a condition in which 20–50% of scalp hair follicles abnormally transition into the telogen (resting) phase and shed their hair. Telogen effluvium is often triggered by physical or psychological stress, or illness. More women than men have telogen effluvium.
- Anagen effluvium. Anagen effluvium is a condition in which the shafts of hairs in the anagen (growth) phase are weakened and break. It is most commonly triggered by radiation therapy and cancer chemotherapy, but may also be related to heavy metal toxicity or exposure to other poisons (Harrison 2009).
- Cicatricial (scarring) alopecias. Hair loss that involves scarring is usually related to an underlying condition or disease. Chronic pressure to the scalp from certain hairstyles can result in traction alopecia, while application of chemicals can also cause long-term inflammation and scarring. Unlike other types of hair loss, cicatricial alopecias are often permanent.
Medical Conditions Associated with Hair Loss
Cardiovascular disease and metabolic syndrome. Androgenetic alopecia may be an indicator of cardiovascular risk. In one study, 80 men and 70 women with early-onset androgenetic alopecia had significantly higher triglyceride as well as total and LDL-cholesterol levels, and lower HDL cholesterol, than men and women without hair loss (Arias-Santiago 2010). In another study, male androgenetic alopecia was correlated with high blood pressure (Ahouansou 2007).
Early onset of pattern hair loss may be a stronger predictor of cardiovascular disease than later-onset androgenetic alopecia. In one study, men with early-onset androgenetic alopecia were more than three times as likely to need coronary artery bypass surgery before age 60 than men with later-onset hair loss and those without hair loss (Matilainen 2001). In addition, early-onset androgenetic hair loss has been linked to an increased risk of metabolic syndrome in men (Banger 2015; Gopinath 2016), while female pattern hair loss has been associated with metabolic syndrome in women (Herskovitz 2013).
Prostate conditions. Research has not consistently found a connection between androgenetic alopecia and benign prostate enlargement, even though both are related to high levels of DHT (Arias-Santiago 2012; Dastgheib 2015; Qi 2014; Carson 2003). However, a review of studies concluded male pattern hair loss occurring at the crown of the head was associated with a 25% increase in prostate cancer risk (Amoretti 2013). Additional evidence found a 56% increase in prostate cancer deaths in men with any balding and an 83% increase in men with moderate balding, pointing to a relationship between male pattern hair loss and fatal prostate cancer (Zhou 2016). Further evidence for this connection is found in research showing that use of finasteride, a 5-alpha reductase inhibitor that reduces serum DHT levels, is associated with reduced overall prostate cancer risk (Wilt 2008; Chau 2015); although it may be less effective at preventing high-grade than low-grade prostate cancers (Hoque 2015).
Because some evidence suggest androgenetic alopecia may correlate with increased prostate cancer risk, men experiencing male pattern hair loss, especially those whose hair loss began at an early age, should monitor their prostate health and take steps to prevent prostate cancer. More information about keeping your prostate healthy is available in the Prostate Cancer Prevention protocol.