Thyroid and Hair Loss in Women: Signs to Watch

Short answer: both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can cause diffuse hair fall in women. A simple blood test (TSH, sometimes with free T4) can check it. Hair usually improves once thyroid levels are treated, but regrowth takes several months.

How the thyroid affects hair

The thyroid gland in your neck makes hormones that set your body's pace. Hair follicles are very active and sensitive to that pace. When thyroid hormone is too low or too high, more follicles may move into the resting phase and shed. This causes diffuse thinning across the whole scalp rather than bald patches.

Thyroid problems are more common in women than in men, and they're often found after delivery or in middle age. Autoimmune thyroid disease can also occur alongside other autoimmune conditions, including alopecia areata.

Signs of an underactive thyroid (hypothyroidism)

• Tiredness and sluggishness
• Weight gain without much change in diet
• Feeling cold
• Dry skin and coarse, dry hair
• Constipation
• Heavier or irregular periods
• Low mood, poor concentration
• Thinning of the outer third of the eyebrows (in some people)
• A puffy face, and a swelling in the neck (goitre)

Signs of an overactive thyroid (hyperthyroidism)

• Weight loss despite a good appetite
• Feeling hot, sweating
• Racing heart, palpitations
• Anxiety, irritability, trouble sleeping
• Tremor in the hands
• Lighter periods
• Fine, soft hair that sheds
• Bulging eyes (in Graves' disease)

Tests

• TSH (thyroid-stimulating hormone): the main screening test.
• Free T4 (and sometimes free T3): to confirm and classify.
• Thyroid antibodies: to look for autoimmune causes.
• Your doctor may also check ferritin, CBC and vitamin D, since these commonly add to hair fall too.

After delivery: postpartum thyroiditis

Some women develop thyroid inflammation in the first year after delivery. It often starts with an overactive phase and is followed by an underactive one. Because postpartum hair shedding is also common, it can be easy to miss. If shedding is unusually long-lasting, or you have other symptoms, ask for a thyroid test.

Treatment and hair recovery

• Hypothyroidism is usually treated with thyroid hormone tablets. The dose is adjusted using follow-up blood tests.
• Hyperthyroidism may be treated with medicines, radioactive iodine or, rarely, surgery.

Hair timeline: once your levels are stable, shedding usually settles over a few months, and visible regrowth follows over the next several months. Some women notice extra shedding while their dose is being adjusted. That's usually temporary.

Tips while you recover

• Take thyroid tablets exactly as prescribed, usually on an empty stomach. Ask your doctor or pharmacist about spacing them from iron and calcium supplements, which reduce absorption.
• Don't change your dose yourself.
• Eat protein at every meal.
• Be gentle with your hair: loose styles, less heat, conditioner every wash.
• Be wary of "thyroid hair" supplements. They're not a substitute for proper treatment, and iodine supplements can make some thyroid conditions worse.

Thyroid, PCOS and iron: often together

A woman with thinning hair may have low ferritin, a thyroid problem and PCOS all at once. Treating one may not fully stop the shedding if another cause remains. That's why a doctor often checks several things together. Read about PCOS hair fall and iron and ferritin.

Questions to ask your doctor

1. Could my hair fall be thyroid-related?
2. Which tests do I need, and how often should they be repeated?
3. How long after my levels normalise should I expect improvement?
4. Do my iron or calcium supplements affect my thyroid tablets?
5. Should I also see a dermatologist?

Quick answers

Can thyroid hair loss be permanent? Usually not. Most women regrow hair once their thyroid levels are stable, although it can take six months to a year to look full again.

Why is my hair still falling after starting thyroid tablets? Some shedding can continue while your dose is being adjusted, and other causes such as low iron may also be involved. Ask your doctor to recheck your levels and your ferritin.

Does the thyroid affect eyebrows too? An underactive thyroid can thin the outer part of the eyebrows in some people. It often improves with treatment.

See a doctor promptly if…

• You notice hair fall along with tiredness, weight change, or feeling too hot or too cold
• You have a racing heart, tremor or unexplained weight loss
• There's a swelling in your neck, or difficulty swallowing
• Your hair fall continued long after delivery
• You're pregnant or planning pregnancy (thyroid levels matter for the baby)

Bottom line

Thyroid problems are a common, treatable cause of hair fall in women. If your shedding comes with any of the signs above, a simple TSH test is a sensible first step. Once your thyroid is balanced, hair usually recovers, slowly.