Telogen effluvium is a common form of temporary hair loss characterized by excessive shedding. It occurs when a significant number of hair follicles prematurely enter the telogen (resting) phase of the hair growth cycle, leading to increased hair fall.

Normally, the hair growth cycle consists of three phases: the anagen (growth) phase, the catagen (transition) phase, and the telogen (resting) phase. Under typical conditions, approximately 85-90% of hair is in the anagen phase, and about 10-15% is in the telogen phase. In telogen effluvium, an increased proportion of hair follicles (sometimes up to 30% or more) prematurely shift from the anagen phase to the telogen phase, resulting in noticeable hair thinning and shedding. If this condition persists for more than six months, it is considered chronic telogen effluvium.

Several factors can trigger telogen effluvium:

* Significant Stress: Major physical or psychological stressors such as divorce, bereavement, job loss, or severe emotional trauma can precipitate hair shedding, typically manifesting 2 to 4 months after the stressful event.
* Postpartum Changes: Many women experience increased hair loss a few months after childbirth. This is due to hormonal shifts where elevated estrogen levels during pregnancy prolong the anagen phase, followed by a rapid return to normal levels postpartum, causing a large number of hairs to enter the telogen phase simultaneously.
* Acute Illnesses: High fevers or severe infections can lead to hair loss approximately 2 to 3 months following the illness.
* Nutritional Deficiencies: Inadequate intake or absorption of essential nutrients like protein, iron, zinc, and vitamins B and D can disrupt the hair growth cycle. Anemia is a common contributing factor.
* Thyroid Disorders: Both an overactive (hyperthyroidism) and underactive (hypothyroidism) thyroid gland can impact hair follicle function and trigger telogen effluvium.
* Medications: Certain drugs are known to cause hair loss as a side effect. These include, but are not limited to, chemotherapy agents, blood pressure medications, antidepressants, antibiotics, beta-blockers, retinoids, and some medications used during or after surgery.
* Sudden Weight Loss: Rapid and significant weight loss, often associated with restrictive diets or conditions like anorexia nervosa, can deprive the body of essential nutrients, leading to hair shedding.
* Hormonal Changes (Other than Postpartum): Menopause, with its associated hormonal fluctuations, can also contribute to increased hair loss in women.
* Autoimmune Conditions: Some autoimmune diseases, such as alopecia areata, directly target hair follicles, causing localized or generalized hair loss on the scalp and other body parts.
* Hair Styling Practices and Other Alopecia Types: Tight hairstyles (e.g., braids, ponytails, extensions) can cause traction alopecia. Additionally, other forms of hair loss like androgenetic alopecia (male/female pattern baldness) are sometimes mentioned in conjunction with or as triggers for telogen effluvium.
* Metal Toxicity: Prolonged exposure to high levels of certain metals can result in hair loss.