Why Am I Losing Hair? 10 Common Causes Explained
Updated: 3 days ago
You are most likely losing hair because of one of a few common triggers: genetics (androgenetic alopecia), a stressful event or illness that pushes many hairs into the shedding phase (telogen effluvium), nutrient gaps such as low iron, thyroid or hormonal changes, or an inflamed scalp. Often more than one cause overlaps.
Losing 50 to 100 hairs a day is normal. If you notice clumps in the shower, a widening part, a thinner ponytail, or visible scalp, something is disrupting your hair cycle and it is worth investigating.
Key takeaways
Shedding (hairs falling out all over) and thinning (hairs getting finer) are different problems with different causes.
Stress-related shedding usually appears about two to three months after the trigger, so the cause is easy to miss.
Genetic hair loss is the most common cause and is progressive, which makes early action valuable.
Blood tests and a scalp examination are the fastest way to separate a reversible cause from a long-term one.
First, Understand How Hair Grows
Every hair follicle cycles through three stages:
Anagen (growth): lasts roughly two to seven years. About 85 to 90 percent of scalp hairs are here at any time.
Catagen (transition): a short phase of around two weeks.
Telogen (rest and shedding): lasts about three months, after which the hair falls out and a new one begins.
Almost every cause of hair loss works by disrupting this cycle: pushing too many hairs into telogen too early, shortening anagen, or gradually shrinking the follicle so it produces finer hairs. For a deeper look at the biology, see our guide on how hair follicles weaken over time.
Shedding vs Thinning: Which Do You Have?
Knowing which pattern fits you narrows the list of likely causes below.
10 Common Causes of Hair Loss
1. Genetics (Androgenetic Alopecia)
Androgenetic alopecia, often called pattern hair loss, is the most common cause of hair loss in both men and women. It runs in families and involves follicles that are sensitive to DHT (dihydrotestosterone), a hormone made from testosterone. Over time DHT shortens the growth phase and shrinks the follicle, so hairs become shorter, finer and eventually stop growing.
In men it typically shows as a receding hairline and thinning crown. In women it more often appears as a widening part and overall loss of density, while the frontal hairline is usually preserved.
Signs: gradual thinning, miniaturised (fine, short) hairs, family history.
2. Stress and Telogen Effluvium
Major physical or emotional stress can push a large share of growing hairs into the resting phase at once. About two to three months later, they shed together. This is called telogen effluvium, and it is the most common cause of sudden, diffuse shedding.
Triggers include surgery, high fever, serious infection, childbirth, crash dieting, bereavement and prolonged psychological stress. Because of the delay, people often cannot connect the shedding to the event that caused it. Most cases settle within about six months once the trigger is resolved, although regrowth takes longer to look visible. We explain this further in how stress affects shedding.
Signs: sudden heavy shedding, hair thinning all over rather than in a pattern, a recent stressful event.
3. Iron Deficiency
Hair follicles are among the most metabolically active tissues in the body, so they react quickly to nutrient shortages. Low iron stores, measured by ferritin, are linked to diffuse shedding, particularly in menstruating women, vegetarians and vegans, and people with heavy periods or digestive absorption problems.
You can have low ferritin without being anaemic, so a standard haemoglobin test may look normal while stores are low. Do not start high-dose iron on your own, as excess iron is harmful. Test first.
Signs: fatigue, pale skin, breathlessness on exertion, heavy periods, diffuse shedding.
4. Thyroid Problems
Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can disrupt the hair cycle. Thyroid hormones help regulate follicle activity, so imbalance may cause hair to become dry, brittle and sparse, sometimes including thinning of the outer eyebrows.
Thyroid hair loss tends to be diffuse and improves once hormone levels are properly treated.
Signs: weight changes, feeling unusually cold or hot, fatigue, palpitations, dry skin, irregular periods.
5. Hormonal Changes
Hormones strongly influence hair. Common hormonal contributors include:
Postpartum shedding: after pregnancy, oestrogen drops and many hairs enter shedding together, usually peaking around three to four months after delivery.
Menopause: falling oestrogen and progesterone can reduce density and make hair finer.
PCOS (polycystic ovary syndrome): raised androgen levels can cause scalp thinning alongside irregular periods and acne.
Starting or stopping hormonal contraception: may trigger temporary shedding in some people.
Signs: shedding linked to pregnancy, cycle changes, menopause or contraceptive changes.
6. Scalp Inflammation and Conditions
Hair grows from the scalp, so an unhealthy scalp environment matters. Inflammation can weaken follicles and increase shedding. Common conditions include:
Seborrhoeic dermatitis (severe dandruff): flaking, redness and itch.
Scalp psoriasis: thick, scaly plaques.
Folliculitis: inflamed or infected follicles, often with tender bumps.
Fungal infections (tinea capitis): patchy loss with scaling, more common in children.
Persistent itch, burning, pain or scaling alongside hair loss deserves a proper examination rather than guesswork with shampoos.
7. Nutrition, Crash Diets and Low Protein Intake
Hair is made largely of keratin, a protein, and building it requires adequate calories, protein and micronutrients. Rapid weight loss, very low-calorie diets, and eating disorders can all trigger shedding, usually a couple of months after the change.
Besides iron, nutrients commonly discussed in hair health include zinc, vitamin D, B12 and folate. A deficiency can contribute, but taking extra when your levels are already normal has not been shown to prevent hair loss, and some supplements, such as high-dose biotin, can interfere with lab test results. Testing is better than guessing.
8. Medications and Medical Treatments
Several medicines list hair loss as a possible side effect. These include some drugs for high blood pressure, depression, acne (high-dose vitamin A derivatives), blood thinning, gout, and some hormonal treatments. Chemotherapy causes a distinct and often dramatic loss because it targets rapidly dividing cells.
Never stop a prescribed medication on your own because of hair loss. Speak with your prescriber, who may adjust the dose or suggest an alternative.
9. Autoimmune Conditions
In alopecia areata, the immune system mistakenly attacks hair follicles, causing round, smooth patches of sudden hair loss. It can affect the scalp, beard and eyebrows. Other autoimmune conditions, such as lupus, can also affect hair. Alopecia areata is unpredictable: regrowth can occur without treatment, but relapse is possible, so specialist assessment is recommended.
10. Hair Styling, Traction and Chemical Damage
Repeated tension from tight ponytails, braids, weaves or extensions can cause traction alopecia, usually along the hairline and temples. Frequent bleaching, relaxing, and high-heat styling can weaken the hair shaft and cause breakage. This is not true follicle loss at first, but prolonged traction can lead to permanent scarring of follicles.
Note the difference: breakage leaves short broken hairs along the strand, while shedding hairs have a small white bulb at the root.
How Do You Know Which Cause Applies to You?
Use these clues as a starting point, not a diagnosis:
Sudden, all-over shedding after illness, surgery or stress: think telogen effluvium.
Slowly widening part or receding hairline with family history: think androgenetic alopecia.
Fatigue, heavy periods, restrictive diet: consider iron or other nutritional gaps.
Itchy, flaky or sore scalp: consider scalp inflammation.
Round, smooth bald patches: consider alopecia areata.
Loss at the hairline from tight styles: consider traction.
Many people have a combination, for example genetic thinning that becomes obvious after a stressful episode triggers extra shedding. That is why a single supplement or shampoo rarely solves the problem.
When Should You See a Professional?
Book an assessment if you notice any of the following:
Shedding that continues for more than three months
Bald patches, or hair loss in a clear pattern
A painful, itchy, red or scaly scalp
Hair loss with fatigue, weight change, irregular periods or other new symptoms
Hair loss after starting a new medication
Rapid change in density, or hair loss at a young age
Early assessment matters most for pattern hair loss, because follicles that have shrunk for a long time are harder to restore than those caught early. You can read about early signs of thinning to see what to look for.
What Happens in a Scalp Assessment?
A good assessment looks at the cause, not only the symptom. It commonly includes:
A detailed history: timeline of shedding, diet, stress, medications, family history, menstrual and pregnancy history.
Scalp and hair examination: checking scalp condition, hair density, hair diameter variation and the pattern of loss.
Magnified follicle analysis: using a dermoscope or trichoscope to assess follicle openings, miniaturisation and inflammation.
Blood tests where appropriate: commonly ferritin, thyroid function, vitamin D and other markers, ordered by a qualified clinician.
This lets you and your practitioner separate reversible causes from long-term ones and build a plan that fits. Learn more about our scalp and follicle assessment, or if you are ready, Start Hair Assessment.
What You Can Do Now
While you wait for an assessment, these steps are safe and sensible:
Track your shedding: note when it started and take monthly photos of your part and hairline in the same light.
Review recent triggers: illness, diet change, new medication, childbirth, stress.
Be gentle: avoid tight hairstyles, limit heat and chemical treatments, and use a mild shampoo.
Eat enough: prioritise adequate protein and a varied diet rather than extreme restriction.
Avoid unproven products: be cautious of any product promising guaranteed regrowth. Treatments should match the actual cause.
Frequently Asked Questions
How much hair loss per day is normal?
Most people lose roughly 50 to 100 scalp hairs a day as part of the normal hair cycle. Consistently losing much more, or seeing thinning, is a reason to investigate.
Can stress really cause hair loss?
Yes. Significant physical or emotional stress can trigger telogen effluvium, where many hairs shift into the shedding phase together. Shedding usually shows up two to three months after the stressful event and often improves within about six months.
Is hair loss from stress permanent?
Stress-related shedding is usually temporary, because the follicles themselves are not damaged. Regrowth is gradual, so visible improvement can take several months. If stress unmasks genetic thinning, that part may continue without treatment.
Can low iron cause hair loss?
Low iron stores, especially low ferritin, are associated with diffuse shedding. Check levels with a blood test before supplementing, since too much iron can be harmful.
What is the most common cause of hair loss?
Androgenetic alopecia, or pattern hair loss, is the most common cause in both men and women.
Will my hair grow back?
It depends on the cause. Shedding caused by stress, illness, nutrition or medication often recovers once the trigger is addressed. Pattern hair loss is progressive and usually needs ongoing management, which works best when started early.
Which test should I ask for?
A clinician may suggest ferritin, thyroid function (TSH), vitamin D and other tests depending on your history. They should be interpreted by a professional rather than self-ordered and self-treated.
When should I worry about hair loss?
See a professional promptly for sudden patchy loss, a painful or scaly scalp, shedding beyond three months, or hair loss with other symptoms such as fatigue or irregular periods.
Conclusion:
Hair loss rarely has a single cause. Genetics, stress, nutrition, hormones and scalp health often interact, and the pattern of your hair loss is a clue to what is driving it. The most useful step is to identify the cause rather than try random products. If you are asking "why am I losing hair?" and the answer is not obvious, a scalp and follicle assessment can give you clarity and a plan.
