Is my hair loss because of my thyroid problem?

Hair fall is one of the most common reasons people get their thyroid checked. Sometimes the thyroid really is the cause. Often it is only part of the story, or not involved at all. Here is how to make sense of it.

How does hair normally grow and fall?

Each hair goes through a cycle. It grows for several years, then enters a resting phase called telogen for a few months, and then falls out so a new hair can grow from the same root. Losing some hair every day is normal.

When the body goes through a stress, such as a high fever, dengue or COVID, surgery, childbirth, crash dieting or a hormone problem, many hairs can switch into the resting phase at the same time. Two to three months later, they all fall together. This is called telogen effluvium. It looks dramatic in the comb or on the pillow, but it is usually temporary, and hair grows back once the cause is fixed.

Can thyroid problems cause hair loss?

Yes. Both thyroid problems can do it:

• Hypothyroidism (underactive thyroid), where hair can also become dry, coarse and brittle.
• Hyperthyroidism (overactive thyroid), where hair often becomes fine and thin.

In both, the typical pattern is diffuse hair loss, meaning thinning all over the scalp rather than in patches. A study from India looking at people with hair loss and thyroid problems found diffuse thinning was by far the most common pattern. Patchy loss and male- or female-pattern thinning were also seen, but much less often.

Does a mildly abnormal thyroid cause hair fall?

Usually not. Many people are told their hair fall is due to a slightly high TSH with a normal T4, a pattern called subclinical hypothyroidism. This mild change is unlikely to be the main cause of hair loss. If your thyroid numbers are only borderline, it is worth looking for other causes too. You can make sense of your report with the thyroid report reader.

Will my hair grow back with thyroid treatment?

In most people, yes, but it takes time. Hair grows slowly, so improvement usually shows over three to six months after the thyroid levels are back to normal.

Do not panic if hair fall seems to get worse for a few weeks after starting thyroxine. As the follicles wake up, they push out the old resting hairs first, and new hairs follow. This shedding usually settles on its own. If it does not, tell your doctor rather than changing your tablet yourself.

Can thyroid medicines themselves cause hair loss?

• Thyroxine (levothyroxine), at the right strength, does not cause long-term hair loss. Too much thyroxine can, because it behaves like an overactive thyroid. That is one reason your doctor checks TSH regularly.
• Medicines for an overactive thyroid, such as carbimazole and propylthiouracil (PTU), can occasionally cause hair thinning. Tell your doctor if you notice it.
• Radioactive iodine for Graves’ disease is not known to cause scalp hair loss.

Some people with an underactive thyroid ask about T3 tablets. Read what liothyronine (T3) tablets are and who they suit.

What is alopecia areata, and is it linked to the thyroid?

Alopecia areata causes round, smooth bald patches, often on the scalp, beard or eyebrows. It is an autoimmune condition, where the immune system attacks the hair roots. Autoimmune thyroid disease, such as Hashimoto’s thyroiditis, is more common in people with alopecia areata, so doctors often check the thyroid.

Treating the thyroid does not usually treat alopecia areata, which follows its own course and is managed by a dermatologist. The simple way to tell them apart is the pattern: patches suggest alopecia areata, while all-over thinning fits thyroid-related or stress-related hair loss.

Can the thyroid affect eyebrows and body hair?

Yes. An underactive thyroid can thin body hair and the outer part of the eyebrows. Loss of eyebrows or eyelashes is called madarosis. It is an old textbook sign of hypothyroidism, but it is not common, and it has other causes too.

Autoimmune thyroid disease also travels with other autoimmune skin conditions such as vitiligo (white patches) and long-lasting hives (urticaria).

Can hair supplements interfere with thyroid tests?

Yes, and this is very important. Many hair, skin and nail supplements contain high amounts of biotin (vitamin B7). Many modern lab tests, including TSH, T4 and T3, use biotin as part of the testing chemistry. Biotin in your blood can confuse these tests.

The result can be a report that looks like an overactive thyroid (low TSH, high T4 and T3) when your thyroid is actually normal. People have been wrongly told they have Graves’ disease because of this. Biotin can upset other hormone tests too.

What to do:

• Always tell your doctor and the lab about any supplement, including “hair vitamins”.
• Ask your doctor or lab how many days before a blood test the supplement should be paused. A gap of a few days is usually enough, but longer may be needed if you have kidney problems.

Some supplements also contain iodine or kelp, which can push the thyroid out of balance in some people. Check the label.

What else commonly causes hair fall in India?

Thyroid is only one cause. Others are very common, especially in Indian women:

• Iron deficiency, even without anaemia, often from heavy periods or a vegetarian diet low in iron.
• Vitamin B12 deficiency, common in vegetarians and people on metformin.
• PCOS, which can cause thinning at the crown from higher androgen levels. Read about the 21-day pill pack for PCOS.
• After childbirth, a few months after delivery.
• Crash diets and low protein intake.
• Male- and female-pattern hair loss, which is genetic.

What should you ask your doctor?

• Is my thyroid level abnormal enough to explain my hair fall?
• Should I also be tested for iron (ferritin), vitamin B12 and vitamin D?
• Could any of my medicines or supplements be the cause?
• Do I need to see a dermatologist as well?

For a full explanation of what each value in your report means, see the guide to the thyroid function test. If thyroid problems, PCOS and hair loss come together, an endocrinologist can look at the whole picture. See who an endocrinologist is or book a consultation.