Understanding Hair Loss: The Most Common Causes

The most common cause of hair loss in adults is pattern hair loss, an inherited, gradual thinning that affects both men and women. Other frequent causes include a temporary shedding called telogen effluvium, the autoimmune condition alopecia areata, hair loss from tight hairstyles, and medical problems such as thyroid disease or low iron. Because each cause is managed differently, working out which one you have is the first and most important step.

A quick look at how hair grows

Each hair follicle runs through its own cycle. The growing phase (anagen) lasts several years on the scalp. A short transition phase (catagen) follows, and then a resting phase (telogen) of a few months, after which the hair falls out and a new one starts growing in the same follicle.

At any time, most scalp hairs are growing and a smaller share are resting. Losing a modest number of hairs each day is normal. Hair loss becomes a concern when the cycle is disrupted: too many hairs enter the resting phase at once, follicles shrink, or the follicle is damaged or attacked.

Pattern hair loss

Pattern hair loss (androgenetic alopecia) is by far the most common type. It runs in families and is driven by how hair follicles respond to androgens, a group of hormones present in everyone. Over time, sensitive follicles produce finer, shorter hairs until some stop producing visible hair at all. This process is called miniaturisation.

In men, it usually shows up as a receding hairline at the temples and thinning at the crown. In women, the hairline usually stays in place while the part widens and the top of the scalp looks less dense. It tends to progress slowly over years, which is why early assessment gives more options. We cover each pattern in more detail in male pattern hair loss and female pattern hair loss.

Telogen effluvium: sudden, diffuse shedding

Telogen effluvium happens when a large number of follicles switch into the resting phase at the same time. A few months later, those hairs fall out together. People often notice handfuls of hair in the shower or on the pillow, and the overall ponytail feels thinner.

Common triggers include a high fever or significant illness, surgery, childbirth, major emotional stress, rapid weight loss, crash dieting, and starting or stopping some medications. The delay between the trigger and the shedding, usually two to three months, means many people do not connect the two. In most cases the shedding settles once the trigger has passed, and regrowth follows over months. Our article on telogen effluvium explains the timeline.

Alopecia areata

Alopecia areata is an autoimmune condition. The immune system targets hair follicles, usually causing smooth, round patches of hair loss on the scalp, beard or eyebrows. The skin in the patch typically looks normal, without scaling or scarring.

The course is unpredictable. Some patches regrow on their own, while some people have repeated episodes or more extensive loss. Because it is an immune condition, it should be assessed by a family doctor or dermatologist, who can discuss medical treatment and look for related conditions.

Traction and hair-care damage

Hair pulled tightly for long periods, such as in tight ponytails, buns, braids, extensions or weaves, can gradually lose density along the hairline and temples. This is called traction alopecia. Caught early, it often improves when the tension is removed. If the pulling continues for years, the follicles can scar and the loss may become permanent.

Harsh chemical treatments, frequent bleaching and high heat can also break hair shafts. That breakage makes hair look thinner, but the follicle itself is usually unaffected, so gentler care often helps.

Medical causes that need attention

Several medical conditions and treatments can cause or worsen hair loss. These include:

• Thyroid disorders, both underactive and overactive
• Iron deficiency, with or without anemia
• Hormonal conditions such as polycystic ovary syndrome
• Low protein intake or certain vitamin deficiencies
• Scalp conditions, including fungal infection and inflammatory skin disease
• Some medications, and treatments such as chemotherapy

A less common group of conditions, called scarring alopecias, causes inflammation that permanently destroys follicles. Warning signs include redness, scaling, pain, burning or itching at the edge of the hair loss, or shiny skin where follicles are no longer visible. These need prompt assessment by a dermatologist, because early treatment aims to stop further loss.

Why diagnosis comes first

It is tempting to go straight to a product or procedure, but treating the wrong cause wastes time and money and can delay care for an underlying condition. A shampoo will not fix a thyroid problem, and scalp injections will not help hair loss caused by low iron until the iron is corrected.

A proper assessment usually includes a detailed history (when it started, how fast, family history, recent illness, diet, medications and hair-care habits), a close look at the scalp and hair, and sometimes a gentle pull test. Your family doctor may order blood tests, often including thyroid function and iron stores. Some people need referral to a dermatologist, and occasionally a small scalp biopsy is needed to confirm the diagnosis.

At HealthPark Medical Aesthetics, a hair consultation starts with this kind of assessment. If something suggests a medical cause, we will encourage you to see your family doctor or a specialist before any cosmetic treatment is considered. For some people, the right answer is treating the underlying problem and waiting, not an aesthetic procedure.

Frequently asked questions

How much hair shedding is normal?

Losing some hair every day is a normal part of the growth cycle, and the amount varies between people and with hair length and washing habits. What matters more is a change from your usual pattern, visible thinning, or patches of loss.

Can I have more than one cause at the same time?

Yes. It is common, for example, to have gradual pattern thinning and then a bout of telogen effluvium after an illness. Sorting out each contributor helps set realistic expectations.

Should I see my family doctor before a hair clinic?

If your hair loss is sudden, patchy, painful or itchy, or you have other symptoms like fatigue, weight change or heavy periods, start with your family doctor. Blood work and medical review can rule out treatable causes.

Is hair loss always permanent?

No. Shedding from stress, illness or childbirth often recovers. Pattern hair loss and scarring conditions tend to progress without treatment, which is why early assessment is helpful.

If you are noticing changes in your hair and want help understanding what might be behind them, a consultation is a chance to review your history, look closely at your scalp and talk through sensible next steps, including whether a referral makes more sense than treatment.