Why Is My Hair Thinning? The 5 Most Common Causes of Hair Loss in Men and Women

Few things prompt a quieter panic than noticing more hair in the shower drain than on your head. Hair thinning is common, deeply personal, and — crucially — rarely mysterious once you know what you're looking at. Here are the five causes that account for the overwhelming majority of cases, and what each one means for men and women.

1. Androgenetic Alopecia (Male and Female Pattern Hair Loss)

This is the big one. Pattern hair loss — sometimes called male pattern baldness or female pattern hair loss — accounts for the majority of all hair thinning.

It's driven by genetics and hormones, specifically the sensitivity of hair follicles to dihydrotestosterone (DHT). Follicles that are genetically predisposed shrink over time, producing progressively finer, shorter hairs until they stop producing visible hair altogether.

The pattern differs by sex. Men typically see a receding hairline and thinning at the crown, eventually meeting in the middle. Women usually notice a widening part and diffuse thinning across the top of the scalp, while the frontal hairline stays largely intact. That difference is why female pattern loss is so often missed early — it creeps rather than announces itself.

It can begin any time after puberty, and it's progressive without treatment. The earlier it's addressed, the more hair there is to save.

2. Telogen Effluvium (Stress-Related Shedding)

If your hair seemed to fall out suddenly rather than gradually, this is the likely culprit.

Telogen effluvium is a shedding response triggered by a shock to the system. Hair follicles are pushed prematurely into their resting phase, and roughly two to three months later they let go all at once. That delayed timing is why people so often fail to connect the shedding to its cause — the trigger happened months earlier.

Common triggers include:

• Severe physical stress, illness, or surgery
• Major emotional stress
• Rapid weight loss or crash dieting
• Childbirth
• Certain medications
• Thyroid disorders

The reassuring news: telogen effluvium is usually temporary. Once the trigger resolves, hair typically regrows over six to twelve months. The frustrating news: it can unmask or accelerate underlying pattern loss at the same time.

3. Nutritional Deficiencies

Hair is metabolically demanding tissue. It's one of the first things the body deprioritises when nutrients run short, which makes deficiencies a frequent and often overlooked cause.

The usual suspects:

Iron. Low ferritin (stored iron) is strongly associated with hair shedding, particularly in women with heavy periods. Levels can be "normal" on a standard blood test and still be too low for optimal hair growth.

Vitamin D. Deficiency is widespread and linked to both shedding and pattern loss.

Zinc. Involved in hair tissue growth and repair; deficiency causes diffuse thinning.

Protein. Hair is largely protein. Inadequate intake — common with crash diets and some plant-based diets without planning — shows up in the hair within months.

B12 and folate. Especially relevant for vegetarians, vegans, and anyone over 50, or those on long-term acid-suppressing medication.

The pattern here tends to be diffuse thinning across the whole scalp rather than a bald patch. A blood panel is the sensible starting point — guessing at supplements wastes both money and hair.

4. Hormonal Imbalances

Hormones govern the hair cycle, so when they shift, hair responds.

In women, the most common driver is polycystic ovary syndrome (PCOS), where elevated androgens cause thinning at the crown alongside acne, irregular periods, and excess facial hair. Thyroid disorders — both underactive and overactive — cause diffuse shedding. The menopause transition brings its own thinning, as oestrogen falls and androgens exert relatively more influence. Coming off hormonal contraception can also trigger a shedding phase.

In men, the predominant hormonal issue is the DHT sensitivity described under pattern loss. Low testosterone, thyroid dysfunction, and elevated prolactin are less common but worth ruling out.

In both sexes, thyroid disease is the great imitator. If you're losing hair alongside fatigue, weight changes, feeling cold, or mood shifts, that combination deserves a thyroid check.

5. Traction Alopecia and Chemical Damage

This is the cause most firmly within your control, and the one most often self-inflicted.

Traction alopecia results from sustained tension on the hair. Tight ponytails, braids, cornrows, extensions, and weaves pull on the follicle root. Done occasionally, the damage reverses. Done habitually, over years, the follicle scars and the loss becomes permanent. It's particularly common along the hairline and temples.

Chemical and heat damage compounds the problem. Repeated bleaching, relaxing, perming, and frequent high-heat styling weaken the hair shaft, causing breakage that mimics thinning. The distinction matters: breakage means the hair is snapping along its length, while true hair loss means it's leaving the follicle. They need different solutions.

Signs you're dealing with traction or damage rather than pattern loss: the thinning is concentrated where tension or chemicals are applied, the hair feels brittle and snaps easily, and the scalp may be tender or show small bumps.

What to Do About It

Hair thinning is a symptom, not a diagnosis, and the five causes above frequently overlap. Pattern loss and a nutritional deficiency can be happening simultaneously; stress-related shedding can unmask what was always there.

A few principles worth holding onto:

Get a proper assessment. A doctor or dermatologist can examine the scalp, look at the pattern of loss, and order relevant blood tests. Pattern, timing, and accompanying symptoms together usually point clearly at the cause.

Act early. Follicles that have shrunk can often be revived. Follicles that have scarred cannot. Every month of delay narrows your options.

Be sceptical of quick fixes. Most over-the-counter "hair growth" shampoos and serums have thin evidence behind them. The interventions with real support — minoxidil, finasteride for men, certain prescription treatments, iron correction where deficient — are unglamorous but effective.

Address the root cause, not just the symptom. No topical product will outrun an untreated thyroid condition, an ongoing crash diet, or a hairstyle that keeps pulling hair out by the root.

The Bottom Line

The most common causes of hair thinning are pattern hair loss, stress-related shedding, nutritional deficiencies, hormonal imbalances, and traction or chemical damage. Most people are dealing with more than one at once.

The single most useful thing you can do is stop guessing. Identify the pattern of your loss, note when it started, and get it properly assessed. Hair thinning is far more treatable than most people assume — but only once you know what you're actually treating.