Top Causes of Hair Loss, Ranked by How Common
The top causes of hair loss are not a long list, and they are not evenly weighted. Pattern hair loss alone accounts for the large majority of cases in both men and women, and shedding driven by illness, stress or nutrition covers most of what remains. This page is the reference catalogue: every significant cause, ordered by how common it actually is, with its signature, whether it is reversible, and what genuinely helps. Prevalence is the organising idea, because knowing what is likely narrows the field faster than knowing what is possible.
Key takeaways
- Pattern hair loss is by far the single largest cause. If you are playing the odds, start there.
- Most of the remainder is shedding, which has a trigger and usually recovers on its own.
- Reversibility varies enormously by cause, so the label matters more than the severity.
- Several causes stack more often than people expect, and stacking is why the picture can look worse than any one cause explains.
- Scarring loss is the one category where delay costs you permanently, so it belongs at the front of the queue.
The top causes of hair loss, ranked by how common they are
Ranking matters because most lists present eight causes as though each were equally likely, which quietly encourages people to chase rare explanations while overlooking the obvious one. Roughly speaking, the distribution looks like this.
| Cause | How common | Signature | Reversible? |
|---|---|---|---|
| Pattern hair loss | Most cases | Slow, regional, spares back and sides | No, but manageable |
| Telogen effluvium | Very common | Fast, diffuse, follows a shock by 2 to 3 months | Yes, usually fully |
| Nutritional shortfall | Common | Diffuse, follows dieting or heavy periods | Yes, once corrected |
| Breakage and traction | Common and underdiagnosed | Short snapped hairs, thinning edges | Yes, if caught early |
| Thyroid and endocrine | Less common | Diffuse, with fatigue or weight change | Usually, with medical care |
| Medication effects | Less common | Follows a new medicine by weeks to months | Usually, via your GP |
| Alopecia areata | Uncommon | Smooth round patches, sharply bordered | Often, unpredictably |
| Scalp disease | Uncommon as a cause of loss | Flaking, itching, redness alongside | Yes, once the scalp settles |
| Scarring alopecias | Rare | Smooth shiny skin, pain or burning, lost pores | No, urgent to act |
If you would rather work from your own symptoms than from a list, the three clue self-check is the page that sorts you into one of these rows. This page is the reference behind it.
Pattern hair loss, the cause behind most cases
Androgenetic alopecia is the single largest entry on any list of the top causes of hair loss, and it is not close. Inherited follicle sensitivity to androgens causes affected follicles to produce progressively finer, shorter hairs over successive cycles, until they produce very little.
The signature is unmistakable once you know it: the loss is regional rather than general. Men see the temples recede and the crown thin. Women see the parting widen with the frontal hairline usually preserved. In both, the back and sides stay dense, because those follicles are typically not sensitive to the hormonal signal.
It progresses over years, not weeks, and it does not resolve on its own. Licensed medicines exist in the UK, and a GP or pharmacist is the right person to discuss what applies to you. For how the condition works, see pattern hair loss explained, and for what sets it off and speeds it up, the triggers and accelerants guide.
Telogen effluvium, the shedding that follows a shock
Telogen effluvium is the body pushing an unusually large batch of follicles into their resting phase at once, typically after a significant physical or emotional event. Those hairs release together two to three months later, producing sudden, alarming, all over shedding.
The delay is the diagnostic feature and the thing most people miss. By the time hair is coming out in the shower, the surgery, fever, birth, crash diet or brutal quarter is months in the past and no longer feels connected. Ask what happened one season ago, not this week.
The good news is real: this cause usually resolves completely once the trigger has passed, because the follicles are healthy and simply out of step. Recovery typically takes six to nine months from when the shedding stops. Detail in the guide to sudden shedding and, for the stress version specifically, stress and hair.
Nutritional shortfalls, especially iron
Hair is metabolically expensive and non-essential, so it is among the first things the body economises on. Two shortfalls dominate.
Iron is the big one, particularly in anyone with heavy periods, a vegetarian or vegan diet, or a history of dieting. The marker that matters for hair is ferritin, which reflects stored iron, and it is worth asking for by name because a full blood count can look normal while ferritin sits at the bottom of the range.
Overall energy and protein intake matters more than any individual micronutrient. Sustained under-eating, whether deliberate or accidental, reliably produces diffuse shedding. Very rapid weight loss is one of the most consistent triggers there is.
Vitamin D and zinc are worth checking where there is reason to suspect a shortfall. Beyond correcting a genuine deficiency, however, supplementing does very little, and taking large amounts of some nutrients, selenium and vitamin A in particular, can itself cause shedding. More is not better here.
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Shop GrowPro GummiesBreakage and traction, the causes that are not really loss
Breakage belongs on this list because it produces exactly the appearance people come here about, while involving no follicle problem whatsoever. The fibre is snapping partway along its length from heat, bleach, aggressive brushing or repeated tension, and the result is reduced volume and see-through ends that read as thinning.
Traction is the tension version. Tight ponytails, braids, weaves and extensions pull steadily at the follicle, and sustained pull causes thinning at the edges, temples and hairline. Traction is genuinely different from every other entry here in one important respect: caught early it recovers fully, and left for years it can become permanent as the follicles scar over. It is simultaneously the most fixable cause and one of the few that can become irreversible through neglect.
The distinguishing test is the hair itself. Broken hairs are short, uneven and blunt-tipped. Shed hairs are full length with a small pale bulb. More in how to reduce breakage.
Thyroid, hormonal and endocrine causes
An underactive or overactive thyroid both affect hair, usually as diffuse thinning accompanied by other symptoms: fatigue, weight change, temperature sensitivity, changes to skin and nails. Thyroid function is a simple blood test and the hair usually improves once levels are corrected.
Other endocrine entries include PCOS, which raises androgen activity and can produce pattern-style thinning alongside irregular periods and acne, and the hormonal transitions of pregnancy and the menopause. Because the female picture is so much richer than a single row can hold, it has its own page: causes of hair loss in women, arranged by life stage.
Medication effects
A range of medicines list hair changes among their effects, including some antidepressants, beta blockers, anticoagulants, retinoids, hormonal contraceptives and chemotherapy agents. The pattern is usually diffuse shedding starting weeks to a few months after beginning the medicine.
The important instruction here is a negative one. Never stop a medicine because you suspect it is affecting your hair. Raise it with the GP who started it, who can weigh whether an alternative exists and whether the timing genuinely fits. Stopping a medicine unsupervised is a far larger risk than the hair change you are trying to address.
Autoimmune and scalp causes
Alopecia areata is the immune system attacking hair follicles, producing smooth, sharply bordered round patches, most often on the scalp but sometimes in the beard or eyebrows. It is uncommon, unpredictable, and often self-limiting, and it warrants a GP because the course varies so widely.
Scalp conditions such as seborrhoeic dermatitis and psoriasis cause inflammation, flaking and itching. They do not usually cause hair loss directly, but the scratching and inflammation that come with them can add shedding, which resolves as the scalp settles. See the flaky scalp guide.
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Why causes stack, and why that confuses people
Presenting the top causes of hair loss as a list implies you have one. In practice two or three overlapping is the norm, and stacking explains most of the cases that seem not to fit any single description.
A common combination: early pattern thinning that has been quietly progressing, plus a stressful year producing a shedding wave, plus heat styling used more often precisely because the hair looks flat. Three causes, one appearance, and each needs a different response. The pattern layer needs a long term plan, the shedding layer needs time and the trigger removed, and the breakage layer needs gentler handling and stops being a problem within weeks.
Practical consequence: when you find one cause, do not stop looking. And when something improves but not completely, that is usually a stacked cause resolving one layer at a time rather than a failure.
Causes that get listed but rarely matter
- Hats. Follicles get their oxygen from blood, not air. Wearing a hat changes nothing.
- Frequent washing. Washing releases already-detached hairs. It does not remove living ones.
- Hard water. It affects how hair feels and how products perform. Evidence that it causes hair loss is weak.
- Short bursts of stress. A difficult week does not shift the hair cycle. Sustained months of it can.
- Cutting hair. Cutting has no influence on what a follicle produces next, and hair does not return thicker for having been cut.
Where cosmetic care fits among the causes
Set against this list, honest positioning is straightforward. For pattern hair loss, autoimmune, endocrine and scarring causes, cosmetics do nothing to the underlying process, and the useful action is medical. For breakage and traction, gentler handling and better protection genuinely address the cause itself, because the cause is mechanical. For everything else, cosmetic care is supportive: it protects the hair you have while the real work happens elsewhere.
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Frequently asked questions
What is the single biggest cause of hair loss?
Pattern hair loss, also called androgenetic alopecia, accounts for the majority of cases in both men and women. It is driven by inherited follicle sensitivity to androgens, progresses slowly over years, and spares the back and sides of the scalp.
Which of the top causes of hair loss are reversible?
Shedding after a shock, nutritional shortfalls, medication effects, scalp inflammation and breakage all typically recover once the underlying issue is addressed. Pattern hair loss is progressive and is managed rather than resolved. Scarring alopecias are permanent, which is why they need attention quickly.
How do I find out which cause applies to me?
Three pieces of information do most of the work: where the thinning sits, how quickly it appeared, and what changed two to three months beforehand. A GP blood test covering ferritin, full blood count, thyroid function and vitamin D rules several causes in or out.
Can more than one cause happen at the same time?
Yes, and it is the norm rather than the exception. Early pattern thinning plus a stress-related shedding wave plus heat damage is a very common trio. Each layer needs a different response, and they tend to resolve on different timescales.
Does hair loss mean something is wrong with my health?
Usually not. The most common causes are genetic or a temporary response to an event. Loss alongside fatigue, weight change, irregular periods or new coarse facial hair is worth investigating, as is anything patchy, painful or scarring.
Do supplements help with any of these causes?
Correcting a genuine, tested deficiency helps. Taking supplements without a deficiency does very little, and high doses of selenium or vitamin A can cause shedding in their own right. Test first rather than guessing.
How long before hair improves once the cause is addressed?
Expect three to six months before visible change and up to a year for density to rebuild, because hair grows roughly a centimetre a month and new growth starts fine and short. Monthly photographs in consistent light show progress the mirror hides.
The short version
Among the top causes of hair loss, one dominates: pattern hair loss explains most cases and needs a long term plan rather than a quick fix. Shedding after a shock and nutritional shortfalls cover most of the rest and usually recover fully. Breakage and traction imitate loss without involving the follicle. Thyroid, medication and autoimmune causes are less common but readily identifiable. Scarring loss is rare and urgent. Work out which row you are in, expect to be in more than one, and let the label rather than the fear set what you do next.
Sources and references
- NHS, Hair loss, on the common causes and on when hair loss warrants medical attention.
- British Association of Dermatologists, Telogen effluvium, on the delayed shedding pattern and expected recovery.
- British Association of Dermatologists, Alopecia areata, on patchy autoimmune hair loss and its variable course.
- NHS, Iron deficiency anaemia, on iron status, who is at risk and how it is tested.
- NHS, Underactive thyroid, on thyroid symptoms including hair and skin changes.
- NHS, Vitamin D, on requirements and on the risks of taking too much.
