This is the most common cause of hair loss. It may involve from 5% to 15% of hairs. Upon close examination, the patient’s overall hair appears to be thinning. Casual observers are rarely aware, because about half of ones hairs need to be lost to be noticeable. But patients themselves see large quantities of hair falling when they comb or brush, & are scared to death.
The normal activity of each hair follicle progresses through 2 main phases:
- Anagen: Hair strand grows continuously for 3-6 years (~90% of hairs)
- Telogen: Resting phase lasting 1-6 months (~10% of hairs)
The hair is shed at the end of Telogen, and Anagen resumes with a new strand. At birth, follicles gradually begin their activity, cycles are not synchronized, so Telogen hairs don’t all fall out together. However, various physical or psychological stressors can cause many follicles to suddenly enter Telogen all at once.
Such triggers can include significant illness, surgery, injury, after childbirth, sudden weight loss, starting or stopping certain medications (in particular birth control or acne pills), and major psychological trauma. I’ve had two friends experienced this upon leaving home. New medications may be another possibility; there’s no good data, but those implicated have included beta-blockers, anticoagulants, retinoids, propylthiouracil, carbamazepine, and immunizations.
Telogen Effluvium occurs 3 to 6 months after its trigger. It usually resolves within 6-12 months. A chronic form of the condition can persist longer, with ongoing diffuse hair thinning, but not total baldness. This is much less common.
Our diagnosis is made clinically (without tests): Diffuse, non-focal hair loss without any evidence of scalp disease. It’s nice if we can identify a trigger event. Dermatologists have a variety of diagnostic tricks involving pulling out hairs, but I don’t refer patients. I might order blood tests such as a thyroid test (TSH), a complete blood count (CBC), ferritin level (for iron-deficiency), and a Vitamin D level. I’d rule out other possibilities by history.
Even if I can’t pinpoint the trigger, I reassure patients that:
- Most people aren’t able to notice;
- Nobody becomes totally bald; and
- Hair will begin to grow back normally within 6 months. If not, I send to Dermatology [have never had to].