Medically Reviewed by Dr Ali, FRCP (Edinburgh), FRCP (London), MBBS, MRCS, LRCP, DCH, DRCOG, MRCGP
Hormonal imbalances are often blamed for hair loss, but they account for only a small percentage of cases. Many factors can cause hair loss, and some shedding is normal. Women may lose hair after childbirth or menopause, and most men experience some hair loss by adulthood. Aging also leads to varying degrees of baldness, mainly due to genetics.
Hair Growth Cycle
Hair follicles go through cycles of growth and rest. During the resting (telogen) phase, hair falls out and is replaced. Unlike some animals that shed hair all at once, human hair growth is staggered, so daily hair loss is normal. A common cause of excessive hair loss is telogen effluvium, triggered by major stressors like illness or surgery. Because the hair cycle lasts months, shedding may occur long after the event but usually resolves as new hair grows.
Thyroid Disease and Hair Loss
Severe, prolonged hypothyroidism or hyperthyroidism can cause diffuse hair thinning across the scalp. Hair usually regrows with proper treatment, but it may take months and could be incomplete. Mild or short-lived thyroid issues rarely cause hair loss. Since the hair cycle is slow, shedding may appear months after thyroid disease begins or even after treatment starts, sometimes leading to the mistaken belief that thyroid medication is to blame.
Hair Loss from Antithyroid Treatment
In rare cases, antithyroid medications like carbimazole or propylthiouracil can cause diffuse hair loss. However, it is often difficult to tell if the shedding is due to the medication or the thyroid condition itself. Switching treatments is usually unnecessary. Radioiodine therapy does not cause hair loss.
Autoimmune Thyroid Disease and Hair Loss
Most thyroid disorders are autoimmune, increasing the risk of other autoimmune diseases. Alopecia areata—an autoimmune condition causing patchy hair loss—is more common in those with autoimmune thyroid disease. It is usually temporary but can sometimes lead to severe baldness. Other autoimmune conditions, like lupus erythematosus, can cause hair loss through scarring. Polycystic ovarian syndrome (PCOS), which is linked to autoimmune thyroid disease, can also cause diffuse hair thinning along with irregular periods, obesity, and acne.
Investigations for Hair Loss
If you’re experiencing significant hair loss, consult your GP. Thyroid disease rarely causes hair loss without other symptoms. Your doctor may recommend tests for other causes, such as iron deficiency, or refer you to a specialist if needed.
What Can I Do?
Hair loss from thyroid issues is usually temporary, but regrowth can take months and may change in texture or color. Be patient and seek emotional support from loved ones or groups like Alopecia UK. The NHS provides useful coping tips.
Be cautious of “miracle cures” and always consult a doctor before trying treatments. NHS Choices and the British Association of Dermatologists offer reliable information on hair loss and approved treatments. Wigs, hairpieces, or makeup can help boost confidence, and NHS support may be available.
Handle hair gently—avoid tight braids, straighteners, and harsh styling. Use wide-tooth combs and professional hair care products. Caffeine shampoos are popular but not proven effective.
Avoid iodine-rich “hair supplements” or “thyroid support” products, as they may interfere with thyroid function or medication. Take iodine supplements only if recommended by your doctor. Maintain a balanced diet and take calcium supplements at least four hours after levothyroxine.
Can Biotin Help Hair Regrowth?
Biotin (vitamin B7) is found in foods like eggs, nuts, and salmon and is often marketed for hair and nail health. While benefits are anecdotal, many supplements contain high doses (5,000–10,000mcg). High-dose biotin can interfere with thyroid blood tests, leading to false readings. If taking biotin, stop a few days before tests and inform your doctor.
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