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Hair loss is rarely as simple as one bad shampoo or a few stressful weeks. You might notice a wider part, a receding hairline, or a shower drain that seems to fill faster than it used to. Those clues matter because the top 7 causes of hair loss look different, progress at different speeds, and need different responses. Some are inherited. Some are temporary. A few point to an underlying health issue that deserves a doctor’s attention.
Here are the most common culprits, along with the details that help tell them apart.
1. Genetics and Pattern Hair Loss
Androgenetic alopecia is the most common form of hair loss, affecting men and women. It’s driven by a mix of inherited sensitivity and hormones, particularly dihydrotestosterone (DHT). In men, it often starts with a receding hairline or thinning at the crown. In women, it tends to show up as a widening part and diffuse thinning over the top of the scalp, while the frontal hairline may stay intact.
The giveaway is gradual change. You may lose hair steadily over years rather than in sudden clumps. A family history of thinning hair is a strong clue, though not a requirement. Pattern hair loss can begin in your 20s, 30s, or later, and it doesn’t mean something else is wrong.
2. Hormonal Shifts and Thyroid Problems
Hormones can push hair follicles into a resting phase or disrupt the growth cycle. Childbirth is a classic example: many women shed heavily around three to six months postpartum. Menopause, starting or stopping birth control, and polycystic ovary syndrome (PCOS) can also trigger thinning. With PCOS, look for irregular periods, acne, and excess facial or body hair alongside the scalp changes.
Thyroid disease is another common driver. Both an overactive and underactive thyroid can cause diffuse shedding. Other clues include fatigue, weight changes, feeling cold or hot, dry skin, and changes in heart rate. A simple blood test can check thyroid function, which is why persistent unexplained shedding is worth investigating rather than guessing.
3. Stress and Telogen Effluvium
Physical or emotional stress can send a large number of hairs into the telogen, or resting, phase at once. The result is telogen effluvium: widespread shedding that often appears two to three months after the trigger. Common triggers include surgery, a severe illness, a car accident, childbirth, bereavement, or a prolonged stretch of poor sleep and worry.
This type of shedding is usually temporary, but it can be alarming. You may lose handfuls in the shower or find hair on your pillow. If the stressor resolves, hair often recovers over six to twelve months. Ongoing stress keeps the cycle stuck, and chronic pain can be part of that load. If pain is a daily factor, understanding what is driving chronic back pain can be one step toward reducing the overall strain on your body.
4. Nutritional Gaps
Hair is not a vital organ, so when nutrients run low, the body prioritizes other functions. Crash diets, restrictive eating, heavy periods, pregnancy, and some plant-based diets without careful planning can leave gaps. The nutrients most often linked to shedding include:
Nutrients most often involved
- Iron and ferritin: Low iron stores can cause shedding even when your hemoglobin is normal.
- Vitamin D: Low levels are common and have been associated with diffuse hair loss.
- Vitamin B12: A deficiency can contribute to poor hair growth, especially with fatigue or tingling hands and feet.
- Zinc: Too little zinc can disrupt hair growth, though too much is not helpful either.
- Protein: Very low protein intake can push hair into a shedding phase.
You don’t need a cabinet full of supplements. Testing beats guessing, especially for iron and vitamin D. A doctor can interpret results alongside your diet, periods, and medical history.
5. Medical Conditions and Autoimmune Disease
Some hair loss is a symptom rather than a standalone problem. Alopecia areata is an autoimmune condition that causes smooth, round patches of loss, sometimes on the eyebrows or beard. Thyroid disease, lupus, and other immune-related conditions can also affect hair. If you have joint pain, rashes, fevers, or unusual fatigue alongside thinning hair, it’s worth looking at the broader picture. Learning the early signs of autoimmune diseases can help you ask better questions at an appointment.
Scalp conditions matter too. Psoriasis, seborrheic dermatitis, and fungal infections can cause itching, scaling, redness, and temporary shedding. Persistent scalp itching is easy to dismiss as dryness, but it can be a clue. This guide to persistent itching and how to tell the causes apart is useful if your scalp is irritated rather than simply thinning. Recurrent skin infections or slow-healing scalp sores can also warrant a look at risk factors for immune deficiency.
6. Medications and Medical Treatments
Many medications can cause shedding as a side effect. Chemotherapy is the best-known example, but blood thinners, some antidepressants, acne medications, anticonvulsants, and certain drugs used for inflammatory arthritis can also affect the hair cycle. The timing is a clue: medication-related shedding often begins weeks to a few months after starting a drug or changing a dose.
Do not stop a prescribed medicine on your own. Instead, note the start date and ask your doctor whether hair loss is a known side effect and whether an alternative exists. If you have an inflammatory condition, it helps to understand the different types of arthritis and why the label matters, since treatment choices and side effects can vary.
7. Hair Care Habits and Traction
Tight braids, weaves, extensions, and repeated chemical relaxers can pull or damage follicles over time. Traction alopecia often starts at the hairline or temples, especially with styles that stay tight for weeks. Heat tools, bleaching, and overlapping chemical treatments can break hair mid-shaft, which looks like loss but is actually breakage.
Trichotillomania, a compulsive hair-pulling disorder, is another cause that deserves compassion rather than blame. It often affects the scalp, eyebrows, or eyelashes and can leave uneven patches. Treatment usually involves therapy, sometimes alongside medication.
How to Narrow Down the Cause
Start with a timeline. Did the shedding begin suddenly or gradually? Did it follow an illness, pregnancy, surgery, new medication, or major stressor? Is the loss patchy, diffuse, or concentrated at the part and temples? Those details are more useful than a single photo taken in bathroom lighting.
Look at the scalp itself. Redness, thick scaling, pain, or smooth bald patches should prompt a medical visit. So should loss that comes with fatigue, weight changes, fevers, joint pain, or unusual infections. A dermatologist can examine the scalp, check for scarring, and order blood tests if needed. In many cases, the cause is treatable or temporary, but the right plan depends on the right diagnosis.
