Diffuse hair shedding is distressing. In many cases, the patient notes an increase in hair on the pillow, or when brushing, or in the shower drain.1 It is usually recognized more readily by women than men.1,2 However, diffuse hair loss can affect both sexes at any age.
In this article, we review the triggers of diffuse hair loss and outline an approach to diagnosis and management.
THE NORMAL HAIR CYCLE
Normally, each hair follicle cycles independently, so that while some hairs are growing, others are resting and others are shedding. Thus, the density of the scalp hair and the total number of scalp hairs remain stable. Most people have about 100,000 scalp hairs, and normally 10% to 15% of these are in the telogen phase.6 Shedding of 100 to 150 telogen hairs per day is normal.5 Anagen hair loss is never normal.
The most common type of diffuse shedding is telogen effluvium, in which anagen-phase hair follicles prematurely transition to the telogen phase, resulting in a noticeable increase in hair shedding at the end of the telogen phase 2 to 3 months later.2,4 Telogen effluvium is a sign of an underlying condition and, thus, is not itself a complete diagnosis.
THE DIFFERENTIAL DIAGNOSIS OF DIFFUSE HAIR LOSS
Telogen Hair Loss
Telogen effluvium has many triggers, and these determine the characteristics of the telogen hair loss.
Telogen effluvium can be acute (lasting < 6 months), chronic (6 months or more), or chronic-repetitive.1,7 If a trigger is acute and short-lived, the telogen effluvium will likely be acute and will resolve. If a trigger is ongoing, if repeated or sequential triggers occur, or if a trigger is not reversed, then the telogen hair shedding can be ongoing.7
Rule out androgenetic alopecia. Important in the differential diagnosis of telogen hair loss is early androgenetic alopecia (pattern hair loss). Early androgenetic alopecia can present as episodic telogen hair shedding before the distinctive pattern of hair loss is seen.8 Androgenetic alopecia is a distinct condition, but the signs of telogen hair shedding can be noted.
Anagen hair loss
Anagen hair shedding is due to the premature termination of anagen hair growth or anagen arrest, after an acute, severe metabolic insult.9 It is most often iatrogenic, caused by treatment with cytotoxic drugs9,10 or radiation.9
Rule out alopecia areata. Important in the differential diagnosis of anagen hair loss is alopecia areata. A detailed history and physical examination to identify the temporal association of possible triggers and any underlying systemic disease should be done in patients with a history of hair shedding. In some cases, further workup is required.
TRIGGERS OF DIFFUSE TELOGEN HAIR LOSS
Triggers of telogen effluvium are numerous.2,4,11–13
Physiologic stress such as surgical trauma,4 high fever,4 chronic systemic illness,4 and hemorrhage11 are well known to cause telogen effluvium 2 to 3 months after the insult. Telogen hair shedding can be experienced 2 to 4 months after childbirth (telogen gravidarum).4
The relationship between emotional stress and hair loss is difficult to ascertain, and hair loss itself is stressful to the patient.14 Historically, acute reversible hair loss occurring with great stress has been reported.11 However, the relationship between chronic diffuse hair loss and psychological stress is controversial.11,14 Evidence for this association appears to be weak, as everyday stresses are likely not enough to trigger hair loss.3,14
Both hypothyroidism and hyperthyroidism can cause diffuse telogen hair loss that is usually reversible once the euthyroid state is restored.9,11 Chronic systemic disorders such as systemic amyloidosis,14 hepatic failure,4 chronic renal failure,4 inflammatory bowel disease,4,14 and lymphoproliferative disorders2 can cause telogen hair shedding. Telogen hair loss has also been reported in autoimmune diseases such as systemic lupus erythematosus and dermatomyositis,14 as well as in chronic infections such as human immunodeficiency virus type 19 and secondary syphilis.11 Inflammatory disorders such as psoriasis, seborrheic dermatitis, and allergic contact dermatitis can all cause diffuse telogen hair loss.7,15
Nutritional causes of diffuse telogen hair loss are zinc deficiency and iron deficiency.11,14 Severe protein, fatty acid and caloric restriction with chronic starvation2,11,14 and crash dieting12 can also induce diffuse telogen hair loss. Malabsorption syndromes and pancreatic disease can precipitate telogen hair shedding.11 Essential fatty acid deficiency can also be associated with diffuse telogen hair shedding usually 2 to 4 months after inadequate intake.11 Vitamin D is an essential vitamin in cell growth, and vitamin D deficiency may be associated with diffuse hair loss.1,7 Biotin deficiency can result in alopecia, but this is a very rare cause of hair loss.14