Hair Loss Causes: Shedding, Pattern, Patches

Hair loss has three common mechanisms, and telling them apart on the scalp is most of the diagnosis: androgenetic alopecia, a genetically driven pattern that thins hair progressively; telogen effluvium, a diffuse shed triggered by an event about three months earlier; and alopecia areata, an autoimmune attack that clears round patches. Normal shedding, meanwhile, is 50 to 100 hairs a day.

Shedding and loss are different problems

The American Academy of Dermatology draws the line clearly. Shedding means more hair than usual is falling out while growth continues normally — the body corrects itself and the density returns. Loss means something is stopping hair from growing, and the density does not return until the cause is dealt with. People arrive at the same complaint, “my hair is falling out”, from both directions, and the useful question is not how much is in the drain but whether the scalp is more visible than it was a year ago.

Pattern hair loss: the common one

Androgenetic alopecia is described by StatPearls as a genetically predetermined disorder caused by an excessive follicular response to androgens, mediated by dihydrotestosterone and 5-alpha reductase. Each growth cycle produces a finer, shorter hair — miniaturization — until the follicle produces nothing visible.

• Prevalence: roughly 50% of the population over a lifetime. Among white men, about 50% by age 50 and around 80% by 70.
• In men: the Norwood-Hamilton pattern — receding frontotemporal corners and thinning at the vertex.
• In women: the Ludwig pattern — diffuse thinning across the crown with the frontal hairline usually preserved, so the part widens rather than the hairline moving. Incidence rises after menopause.
• Treatment: topical minoxidil and oral finasteride are the two FDA-approved options.

Telogen effluvium: the shed that started months ago

About 85% of scalp hair is in the growing phase and 15% resting at any moment. A shock pushes far too many follicles into resting at once, and they all release together when the next cycle begins. The delay is what disguises it: on average around three months, with a range of one to six.

Triggers include childbirth, surgery, major trauma, high fever and severe infection, crash dieting and low protein intake, iron deficiency, an underactive thyroid, and medications such as beta-blockers, retinoids and anticoagulants. Acute telogen effluvium is defined as lasting under six months, and the AAD notes the excess shedding usually stops within six to nine months as the body readjusts. It recovers without treatment; what it needs is the trigger identified and the deficiency, if any, corrected.

Alopecia areata: round patches, immune driven

NIAMS describes it as the immune system attacking hair follicles. Hair falls out suddenly in round or oval patches, often with a tingling, burning or itching sensation beforehand, and “exclamation point” hairs — narrower at the base than the tip — at the edges. Most people develop it in their teens, twenties or thirties. The follicle is inflamed rather than destroyed, which is why hair frequently regrows. Its full symptom picture, including the nail changes it causes, is in alopecia symptoms.

Causes that are none of the three

• Traction alopecia from tight braids, ponytails and extensions, worst along the hairline
• Scarring (cicatricial) alopecias, where the follicle is destroyed and the loss is permanent — redness, scaling, pain or shiny scarred skin make this urgent
• Scalp infections, notably tinea capitis in children
• Anagen effluvium, the rapid loss caused by chemotherapy
• Thyroid disease, iron deficiency and nutritional shortfalls, which often act through telogen effluvium

How the cause gets identified

A dermatologist reads the distribution first — diffuse, patterned or patchy — then examines the scalp surface for redness, scaling or scarring, checks whether hairs pull out easily, and orders blood work when a systemic trigger is plausible. Getting this right early matters most for the conditions that respond to prompt treatment and for scarring types, where waiting costs follicles permanently. The specifically female causes, which include several the general picture glosses over, are in hair loss in women causes.

This content is informational and does not replace medical consultation, diagnosis, or treatment.