Diffuse Hair Loss: Growth Cycle, Causes, and Treatments

Diffuse hair loss is a common complaint and cause of significant emotional distress. Education about the hair growth cycle and informing patients that hair growth requires a long period of time are essential to help limit the patients’ anxiety.^[1]

Hair Growth Cycle

Hair development is a continuous process, with each hair follicle undergoing 10 to 30 cycles in its lifetime.^[2]

The hair growth cycle consists of 4 distinct phases

• Growth (anagen)
• Regression (catagen)
• Rest (telogen)
• Shedding (exogen).

Each hair follicle cycles independently, so that while some hairs are growing, others are either resting or shedding. This process keeps the density and the total number of hair strands stable. Most people have about 100,000 scalp hairs at a time, and normally 10% to 15% of these are in the telogen phase. It is considered normal for individuals to shed about 100 to 150 telogen hairs per day.^[2]

Anagen (growing) phase

The anagen phase can last 2 to 8 years. During each anagen phase, hair follicles produce an entire hair shaft from root to tip. Anagen hair shedding is never normal and results in premature termination of anagen hair growth or anagen arrest secondary to an acute severe metabolic insult. Hair loss during the anagen phase is most commonly caused by chemotherapy or radiation therapy.^[2] Over time, the length of the anagen phase decreases, resulting in weaker and thinner hair after each cycle.^[3]

Catagen (regression) phase

The catagen phase lasts about 2 weeks. During this phase, each hair follicle regresses and detaches from the dermal papilla, resulting in apoptosis of epithelial cells in the bulb of the hair follicle.^[3,4]

Telogen (resting) phase

The telogen phase lasts 2 to 3 months, with around 10% to 15% of the total scalp hair in this phase at any time. During this phase, while the old hair is resting, new hair may be starting to develop at the base of the hair follicle. Many anagen hairs entering the resting phase prematurely with excessive shedding and noticeable thinning is known as telogen effluvium.^[3]

Exogen (shedding) phase

The exogen phase coincides with the end of the telogen phase and the start of a new anagen phase. During this period the new developing hair continues to move upward pushing the old hair, resulting in shedding of the old hair. Approximately 100 to 150 hairs normally fall out daily.^[3]

Telogen Effluvium

Telogen effluvium is a form of diffuse, nonscarring hair loss that can present either as a transient or chronic loss of hair.^[5] It is a frequent reason for hair loss. In telogen effluvium, the number of hair follicles in the telogen phase increases, resulting in premature shedding of hair.

Hair loss can be due to a wide variety of causes: childbirth, infection, lack of appropriate nutrition, endocrine disorders, drugs, environment, and stressful situations.^[6] Because telogen effluvium is a nonscarring alopecia, hair regrowth is possible.

Acute vs. chronic telogen effluvium

Classic acute telogen effluvium is generally self-limiting and resolves within 6 to 9 months. However, in some patients, hair shedding may be continuous, lasting longer than the average period of time. Chronic telogen effluvium contrasts with the more common acute telogen effluvium by its persistence and its tendency to fluctuate over many years. Despite the prolonged period, like acute telogen effluvium, chronic telogen effluvium does appear to be self-limiting.^[7]

Diagnosing telogen effluvium

A careful clinical history is essential and may be the most important tool for physicians to determine the cause of the patient’s hair loss. In patients complaining of increased hair shedding, clinicians should investigate for potential triggers 3 months prior to the development of hair loss, including drug intake, systemic illness, or weight loss.^[8]

While examining the scalp, the degree and pattern of hair loss should be noted. The scalp should be examined for inflammation, erythema, and scaling, indicating a possible underlying inflammatory process.

Physicians may also perform the hair-pull test, where they hold a small section of hair, about 50 strands, from different parts of the scalp and gently tug on it. If more than 10% of the hair strands fall out, the test is positive for active hair loss. In telogen effluvium, patients will have a positive hair-pull test.^[1] Hair pull tests are done when the hair has not yet been washed for the day.

Aside from a physical exam, blood tests such as complete blood count with ferritin level, thyroid stimulating hormone level, and complete metabolic panel may be ordered if there is suspicion for iron deficiency, thyroid disease, or vitamin or mineral deficiency. For example, compared to normal controls, serum zinc levels were shown to be significantly lower in women with hair loss and were improved with zinc supplements.^[9] If syphilis or a systemic autoimmune disease is suspected, serological testing may be required.

If other diagnostic testing have not identified the cause and the patient continues to suffer from hair loss, the physician may consider doing a scalp punch biopsy to examine the tissue under a microscope for histopathological information.^[10]

Treatment of Hair Loss

Overall approach

Our current treatments for hair loss slow down the process by either keeping anagen-hair in the anagen phase for longer periods of time or accelerating the telogen- anagen transition phase so that the hair follicle can start to grow a new hair shaft and push the old resting hair out. In cases where there is inflammation, anti-inflammatory medications may be used to reduce inflammation.

Treating telogen effluvium

The main treatment for telogen effluvium is to determine the triggering factor. Once the trigger has been identified, removed, and/or treated, hair loss will generally decrease but can persist for up to 6 months, with regrowth following afterwards.^[11]

Nutritional supplementation

If a lack of certain nutrients was determined to be contributing to the hair loss, supplementation can help decrease hair loss and promote hair growth. For example, in one study, patients were given a 6-month supplementation of omega 3, omega 6, and antioxidants ((lycopene, vitamin C, and vitamin E). It was shown that this supplementation improved hair density, reduced the percentage of hair in the telogen phase, and 89.9% of subjects self-reported a reduction of hair loss at 6 months.^[12] Of note, patients with telogen effluvium were specifically excluded in this study.

What is the role of topical minoxidil?

Another common treatment for hair loss is minoxidil. Minoxidil (known by the brand name Rogaine®) is a hair loss treatment approved by the U.S. Food and Drug Administration for androgenic alopecia that is available over the counter. Minoxidil also appears to reduce hair shedding in telogen effluvium.^[13] The product is available in either liquid or foam. Applying topical minoxidil to the scalp at least once daily can be useful for chronic diffuse telogen hair loss.^[2]

It is important that patients use the product consistently to see result. Perhaps more importantly, continued use of the minoxidil is imperative to maintain any results and discontinuation will lead to a return the original trajectory of hair loss prior to use. Scalp irritation and unwanted hair growth on the face and neck are some possible side effects.

Practical Tips

• Hair loss treatment are aimed at reducing inflammation, prolonging the anagen (growth) phase, and acclerating the telogen-anagen (resting to growth) transition of the hair cycle
• Recalling events that occurred 2 to 3 months prior to onset of hair loss to determine possible triggering factors for telogen effluvium
• Minoxidil has also been shown to be an effective treatment to help reduce hair shedding and must be used continuously