In short
Hair loss has several distinct causes with different patterns and treatments — from genetic thinning to iron deficiency, thyroid problems, and stress-related shedding.
On your report
Ferritin, TSH
On this page
01
The Main Categories
The most common cause overall is androgenetic alopecia — genetic pattern hair loss — which in men typically shows up as a receding hairline and thinning crown, and in women more often as diffuse thinning across the top of the scalp while the hairline stays intact. It's gradual, progressive, and runs in families.
A different and often confusing pattern is telogen effluvium: diffuse shedding that starts suddenly, usually two to three months after a triggering stressor such as a major illness, surgery, significant weight loss, childbirth, or a period of intense stress. It looks alarming because so much hair falls out at once, but it's typically temporary and regrows once the trigger resolves.
02
Other Causes Worth Ruling Out
Iron deficiency and thyroid dysfunction (both an underactive and an overactive thyroid) are common, treatable medical causes of diffuse hair thinning, and are worth checking with blood tests before assuming shedding is simply stress or aging. Certain medications, crash dieting, and some autoimmune conditions can also cause hair loss.
Alopecia areata is different again: it causes distinct round, smooth bald patches rather than diffuse thinning, and results from the immune system attacking hair follicles. It's unpredictable — it can resolve on its own or persist — and is generally best evaluated by a dermatologist given how differently it's managed.
03
How It's Evaluated
A dermatologist can often narrow down the cause from the pattern of loss alone — diffuse versus patchy, gradual versus sudden — combined with a scalp exam. Blood tests checking ferritin (iron stores) and thyroid function are commonly ordered for diffuse thinning, since both are straightforward to treat once identified.
A scalp biopsy is occasionally used when the cause isn't clear from the pattern and exam alone, particularly to distinguish between different causes of patchy or scarring hair loss.
04
Treatment
For genetic pattern hair loss, topical minoxidil is available without a prescription and can slow loss and support some regrowth with consistent long-term use; prescription oral medications are another option, primarily for men, that block the hormone driving the pattern. Both need to be continued to maintain benefit — stopping typically lets the underlying pattern resume.
Telogen effluvium generally resolves on its own within several months once the triggering stressor has passed, and iron deficiency or thyroid-related hair loss improves once those underlying levels are corrected. Alopecia areata is treated with anti-inflammatory approaches, most often corticosteroid injections into the affected patches for limited cases.
05
When to See a Doctor
Sudden, patchy, or rapidly progressive hair loss — as opposed to the slow, gradual thinning typical of genetic pattern loss — is worth a dermatology evaluation rather than waiting to see if it resolves.
Because so many treatable causes exist, hair loss is rarely something to just accept without at least checking iron and thyroid levels first, especially when it's new, diffuse, or happening faster than would be expected from family pattern alone.
Values mentioned in this story
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Sources
- Hair Lossmedlineplus.gov
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