Most people look up the reasons for hair fall after weeks of finding hair on the pillow, and many type it as “baal jhadne ka karan”. The American Academy of Dermatology (AAD) lists 18 causes, and the cause decides whether hair grows back on its own, needs treatment, or needs care quickly to prevent permanent loss.
For treatment, tests and daily care for every type, see our complete guide to hair loss in India.
Reasons for hair fall: causes, clues and the check that helps
Losing 50 to 100 hairs a day is normal, according to the UK National Health Service (NHS). Beyond that, how the hair falls is the biggest clue. The table pairs each common cause with what you might notice, who it usually affects and what a doctor would check.
| Cause | Clues | Who, typically | The check that helps |
|---|---|---|---|
| Pattern hair loss (inherited) | Slow thinning; receding temples or crown in men; widening parting in women | Men and women; can start in the teens, more common with age | Scalp examination; family history |
| Temporary shedding (telogen effluvium) | Sudden shedding all over, a few months after fever, childbirth, surgery, stress or a crash diet | Any age; common in women aged 21–30 in one Indian study | History of the past six months; a gentle pull test |
| Long-lasting shedding (chronic telogen effluvium) | Shedding for more than six months without a widening parting | Mostly women; commonest at 30–40 in the same study | Blood tests to look for a cause that has not gone away |
| Low iron, protein or zinc | Diffuse thinning; tiredness, paleness, heavy periods or a restricted diet | Women with heavy periods; people on restricted diets | Haemoglobin and ferritin; diet history |
| Thyroid disease | Thinning all over, sometimes clumps in the brush; weight change, feeling cold or hot | Anyone with an underactive or overactive thyroid | Thyroid-stimulating hormone (TSH) blood test |
| Hormonal imbalance, such as polycystic ovary syndrome (PCOS) | Thinning at the parting with irregular periods, acne or excess facial hair | Women of reproductive age | Period history; hormone tests chosen by the doctor |
| Medicines | Shedding a few months after starting a new medicine | Anyone | Review with the doctor who prescribed it; never stop it yourself |
| Alopecia areata | Round, smooth bald patches; sometimes eyebrows or beard | Any age | Examination; the doctor may check thyroid |
| Tight hairstyles and chemical treatments | Thinning at the hairline or where hair is pulled; broken hairs | People who often wear tight plaits, buns or extensions, or colour and straighten | History of hair care; early change of style |
| Scalp infection or psoriasis | Scaly or inflamed patches, broken hairs, small black dots | Any age | Examination; treatment of the infection or psoriasis |
PCOS was renamed polyendocrine metabolic ovarian syndrome (PMOS) in 2026; reports may use either name. More than one cause can be present at once, which is why a doctor looks at the whole picture.
What Indian clinics find
A population study of 1,005 men aged 30 to 50 in Bengaluru found pattern hair loss in 58%, rising from 47.5% at 30–35 to 73.2% at 41–45. Most had early grades, which is when treatment works best.
In women, Indian hospital studies disagree on the commonest cause. A study of 180 women with diffuse hair loss in Kalaburagi, Karnataka, found temporary shedding in 64%, long-lasting shedding in 16% and pattern hair loss in 12%. A later research letter on 100 women at another Indian hospital found the reverse: pattern hair loss in 61%, temporary shedding in 25% and long-lasting shedding in 14%.
The two clinics used different definitions and saw different patients, so neither number is “the” answer for India. What both show is that women’s hair fall is not just “stress hair fall”: pattern hair loss is common, and low iron turned up across all types.
Hair fall in women: iron, thyroid, PCOS and childbirth
- Low iron. In the Karnataka study, psychological stress and iron-deficiency anaemia were the most common factors behind temporary shedding, and among women with pattern hair loss whose ferritin was tested, 14 of 17 had low levels. In the second study, about half the women had anaemia.
- Thyroid. AAD says treating thyroid disease can reverse the hair loss it causes. In the second study, 14% of women had hypothyroidism, and they mostly had pattern-type thinning.
- PCOS and hormones. AAD names PCOS as a common cause of hormonal imbalance that can thin scalp hair. Stopping some birth control pills can cause a temporary imbalance too.
- Childbirth. Heavy shedding a few months after delivery is common and settles; most people regain normal fullness within 6 to 9 months.
Our guide to blood tests for hair fall explains which of these checks are worth doing, and our guide to hair fall after fever or illness covers shedding after childbirth and infections.
Hair fall in men: mostly inherited
In men, inherited pattern hair loss is by far the most common reason. AAD says the shrinking of follicles can begin as early as the teens but usually starts later, and the first sign is often a receding hairline or a thin spot on the crown. Without treatment it continues, and the earlier treatment starts, the better it works. Our guide to the stages of hair loss shows how doctors grade it.
Men also get temporary shedding after illness or a crash diet, alopecia areata, scalp infections and medicine-related loss. Sudden hair fall in a young man is not always pattern loss, so a doctor’s look is worth it before buying treatments.
Smoking and hair loss: what the studies show
Smoking is linked with pattern hair loss in men, but the evidence is from observational studies, which can show a link, not prove cause.
- A 2007 survey of 740 Taiwanese men aged 40 to 91 found that smokers had 1.77 times the odds of moderate or severe pattern hair loss after allowing for age and family history. Men smoking 20 or more cigarettes a day had 2.34 times the odds.
- A 2024 meta-analysis pooled eight observational studies. Men who had ever smoked had 1.82 times the odds of pattern hair loss compared with men who never smoked, and among men who already had it, smokers had higher odds of it progressing to an advanced stage.
No study has tested whether quitting slows hair loss, and family history mattered far more than smoking in the Taiwan survey. Still, stopping smoking protects your heart, lungs and blood vessels; if you want help quitting, ask your doctor.
Hair problem or hair loss? Breakage, dandruff and scalp conditions
Not every hair problem is hair loss from the root. Hairs that fall from the root have a small white bulb at the end. Short hairs without a bulb have broken, usually from heat, colouring, straightening or rough combing. AAD warns that repeated damage can, over time, destroy follicles and leave permanent bald spots, so gentler care matters.
Ordinary dandruff is not on AAD’s list of causes. Scaly, inflamed patches with broken hairs or small black dots are different: AAD says these can be a scalp infection, which needs treatment, after which hair tends to regrow. Scalp psoriasis can also cause hair loss. Our guide to home remedies for hair fall covers gentle hair care.
When to see a doctor
These are the main warning signs; the hub has the full list of hair-loss warning signs.
Emergency: get help now
- A painful, swollen or pus-filled scalp patch with fever or feeling very unwell.
- Sudden, heavy hair loss with vomiting, confusion, or numbness or weakness in the hands or feet. Some poisons, including thallium and arsenic, cause hair loss.
Prompt review: within days to a few weeks
- Round bald patches, or loss of eyebrow, eyelash or beard hair.
- Smooth, shiny bald areas, or burning, itching or pain where hair is thinning; these can signal scarring hair loss, which cannot regrow once follicles are destroyed.
- Hair fall with tiredness, paleness, heavy or irregular periods, weight change, acne or excess facial hair.
- Hair loss you think a medicine caused. Do not stop the medicine; ask the doctor who prescribed it.
Routine review
- A widening parting or receding hairline, or shedding that lasts beyond six months.
How Disha can help
Disha is an AI health coach that chats and calls in Hindi, English and Hinglish. Once your doctor has found the cause, it can help you eat enough protein and iron from familiar food, avoid crash dieting, and keep up sleep and movement. It does not diagnose hair loss, interpret tests, prescribe or provide emergency care, and it does not replace your doctor. Read how Disha coaching works.
This is not medical advice. This page is general education for adults (18+), not a diagnosis or treatment plan. Hair loss in children needs a doctor’s check. Do not start, stop or change any medicine or supplement because of this page. In an emergency, call 112.
Frequently asked questions
What are the most common reasons for hair fall?
Inherited pattern hair loss is the most common cause worldwide, in both men and women. Temporary shedding a few months after fever, childbirth, surgery, stress or a crash diet is the next big group. Low iron, thyroid disease, PCOS, some medicines, tight hairstyles, alopecia areata and scalp infections are other common reasons. A doctor’s examination is the quickest way to tell them apart.
Does smoking cause hair loss?
Smoking is linked with pattern hair loss in men. A 2024 meta-analysis of eight observational studies found that men who had ever smoked had 1.82 times the odds of pattern hair loss, and heavier smoking was linked with higher odds. These studies cannot prove smoking is the cause, and family history matters more. Quitting is worthwhile for your heart and lungs either way.
Why has my hair suddenly started falling so much?
Sudden, heavy shedding all over the scalp is often temporary shedding, which starts a few months after a fever, childbirth, surgery, major stress, a crash diet or a new medicine. It usually settles by itself. Think back over the past six months for a trigger. If there is none, if you see round patches, or if you feel unwell, see a doctor.
Is hair fall in your 20s normal?
Some daily shedding is normal at any age: 50 to 100 hairs a day. Thinning in your 20s is common but worth checking. In one Indian study of women, both temporary shedding and pattern hair loss were most common between 21 and 30, and pattern loss in men can begin in the teens. Early checks help, because treatment for pattern loss works best when started early.
Which doctor should I see for a hair problem?
A dermatologist usually leads hair-loss care. Your family doctor can start with an examination and basic blood tests, such as haemoglobin and thyroid. An endocrinologist or gynaecologist may help with thyroid problems or PCOS, and a mental-health professional with hair pulling or distress. NHS advises seeing a doctor before paying for a commercial hair clinic.
Can stress alone cause hair fall?
Yes. A major stressful event can trigger heavy shedding a few months later, and in one Indian hospital study psychological stress was the most common factor behind temporary shedding in women. Stress-related shedding usually stops once the stress eases, and hair regains its fullness within 6 to 9 months. Stress can also sit alongside another cause, such as low iron, so get checked if it lasts.
Does dandruff cause hair fall?
Ordinary dandruff is not among the causes of hair loss that dermatology bodies list. Scaly, inflamed or itchy patches with broken hairs or small black dots are different: they can be a scalp infection or psoriasis, which can cause hair loss and need treatment. Hair tends to regrow once the condition clears. See a doctor if scaling comes with patches of thinning.
Sources
- American Academy of Dermatology. Hair loss: Who gets and causes. Accessed November 2026. Supports: the list of causes; hereditary hair loss as the most common cause worldwide, possible from the teens, first signs in men and women, and better results with earlier treatment; PCOS and stopping birth control pills; thyroid treatment reversing loss; medicines and not stopping them; 6–9 months to regain fullness after stress; hair-care damage leading to permanent bald spots; scalp infection with black dots; scalp psoriasis; scarring alopecia; poisons.
- NHS. Hair loss. Current patient guidance. Supports: 50–100 hairs a day is normal; temporary causes; seeing a doctor before a commercial hair clinic.
- Krupa Shankar DS, Chakravarthi M, Shilpakar R. Male androgenetic alopecia: population-based study in 1,005 subjects. International Journal of Trichology, 2009. Population study. Supports: 58% prevalence in men aged 30–50 in Bengaluru; 47.5% at 30–35 and 73.2% at 41–45; grades I–III most common.
- Malkud S. A hospital-based study to determine causes of diffuse hair loss in women. Journal of Clinical and Diagnostic Research, 2015. Observational study. Supports: 180 women; telogen effluvium 64%, chronic telogen effluvium 16%, female pattern hair loss 12%; telogen effluvium and pattern loss commonest at 21–30, chronic shedding at 30–40; stress and iron-deficiency anaemia as the commonest factors; low ferritin in 14 of 17 tested women with pattern loss.
- Agarwal S, Mendiratta V, Yadav P, Chander R. Diffuse hair loss in females. Indian Dermatology Online Journal. Research letter. Supports: 100 women; pattern hair loss 61%, telogen effluvium 25%, chronic telogen effluvium 14%; hypothyroidism in 14%, mostly with pattern loss; about half anaemic; PCOS in 7%.
- Su LH, Chen TH. Association of androgenetic alopecia with smoking and its prevalence among Asian men: a community-based survey. Archives of Dermatology, 2007. Cross-sectional survey. Supports: 740 men aged 40–91; odds ratio 1.77 for smoking and 2.34 for 20 or more cigarettes a day, adjusted for age and family history.
- Gupta AK, Bamimore MA, Talukder M. A meta-analysis study on the association between smoking and male pattern hair loss. Journal of Cosmetic Dermatology, 2024. Meta-analysis of observational studies. Supports: eight studies, all observational; pooled odds ratio 1.82 for ever smoking; higher odds with heavier smoking; higher odds of progression in smokers; no randomised trials.
- American Academy of Dermatology. Alopecia areata: Causes. Accessed November 2026. Supports: alopecia areata as an autoimmune disease affecting any hair-bearing area; its link with thyroid disease.
Related reads
- Hair loss in India: causes, tests, treatment and daily care: the full overview, including treatment; this page goes deeper on causes and their clues.
- Blood tests for hair fall: which tests are useful and which are over-ordered.
- Stages of hair loss: how doctors grade thinning in men and women.
- Home remedies for hair fall: what you can do at home, rated by the evidence.
- All hair loss articles: every Disha guide on hair fall and thinning.
- BMI calculator with Indian cut-offs: a screening number if weight change or PCOS is part of the picture.
