Thyroid and Hair Loss: How Your Thyroid Affects Thinning Hair

Can thyroid problems cause hair loss?

Yes. Your thyroid makes hormones that set the pace for almost every cell in your body, including the cells in your hair follicles. When the thyroid makes too little hormone (hypothyroidism) or too much (hyperthyroidism), hair growth can slow and more hairs can shed than usual.

Dry, thinning hair is a recognized symptom of an underactive thyroid (NIDDK), and hair loss is also listed among the symptoms of an overactive thyroid (American Thyroid Association). The American Academy of Dermatology notes that treating the thyroid disease can reverse the hair loss (AAD).

This matters for women in particular. Women are five to eight times more likely than men to have thyroid problems (American Thyroid Association), and the 40s and 50s are when many women first notice their hair changing for several reasons at once.

By the numbers

Thyroid and hair at a glance

5–8×more likely: women vs men with thyroid problemsSource: American Thyroid Association

50–100hairs a day is normal sheddingSource: AAD

6–9 monthsfor hair to regain fullness after shedding stopsSource: AAD

How thyroid hormones affect hair follicles

Each hair grows for years, rests for a few months, then falls out so a new hair can start. Laboratory research on human scalp follicles has shown that thyroid hormones act on the follicle directly, helping keep hairs in their growth phase (van Beek 2008). When thyroid levels are off, more follicles can slip into the resting phase at the same time, and a few months later those hairs shed together.

That timing is why thyroid-related thinning can feel confusing. The hair loss often shows up weeks or months after the thyroid problem began, and it can lag behind treatment too.

What thyroid hair loss looks like

Thyroid-related hair loss usually has a few features in common:

• It's diffuse. Hair thins evenly across the whole scalp rather than in one bald patch or only along the part.
• Texture can change. Hair may feel drier, coarser or more brittle, especially with an underactive thyroid (Office on Women's Health).
• Other symptoms come along. Tiredness, feeling cold, weight gain, dry skin and heavier periods point toward an underactive thyroid. Feeling hot, a racing heart, trouble sleeping, weight loss and lighter periods point toward an overactive one.

Hypothyroidism vs hyperthyroidism

Symptom lists are from NIDDK and the American Thyroid Association. Not everyone has every symptom, and many overlap with perimenopause, which is one reason a blood test matters.

Autoimmune thyroid disease and patchy hair loss

Round, smooth bald patches are a different condition called alopecia areata. It isn't caused by thyroid hormone levels, but it is linked to autoimmune thyroid disease: a review of 50 studies found that people with alopecia areata had higher odds of thyroid dysfunction and thyroid antibodies (Lee 2019). If you have patchy hair loss, a dermatologist may check your thyroid as well.

Is it your thyroid, menopause or something else?

In midlife, thyroid problems rarely act alone. Several causes of thinning are common at the same age, and two or three can overlap:

• Female pattern hair loss. The most common cause of hair loss in women. It shows up as a widening part and thinning on top, while the front hairline usually stays (AAD). It tends to progress slowly without treatment. Read more in hair loss during menopause.
• Shedding after a trigger (telogen effluvium). Illness, surgery, major stress or a high fever can cause a wave of shedding a few months later. Hair usually regains its fullness within six to nine months once the trigger passes (AAD).
• Low iron. Heavy perimenopausal periods can drain iron stores. A meta-analysis of more than 10,000 participants found that women with non-scarring hair loss had lower ferritin levels than women without it (Treister-Goltzman 2022).
• Medications. Some medicines can trigger shedding, including, rarely, thyroid medicine itself in the first few months (see below).

Tests to ask for

A clinician will usually start by asking about your symptoms, your periods, recent illness or stress, and any medicines or supplements. Common blood tests for thinning hair include:

• TSH (thyroid-stimulating hormone). The usual first screen for both an underactive and an overactive thyroid. Free T4 is often added if TSH is abnormal.
• Thyroid antibodies, in some cases, to look for autoimmune thyroid disease such as Hashimoto's or Graves'.
• Ferritin and a complete blood count, to check iron stores and anemia.

Does thyroid medication cause hair loss?

Sometimes, briefly. The prescribing information for Synthroid (levothyroxine) tells patients that partial hair loss may occur rarely during the first few months of treatment and is usually temporary (Synthroid label). Hair loss is also listed among the effects of taking too much thyroid hormone, which is one reason your dose is checked with follow-up blood tests.

Never stop or change thyroid medicine on your own because of shedding. Bring it up with your prescriber, who can check whether your dose is right and whether something else is going on.

Will hair grow back after thyroid treatment?

Often, yes. Hair loss from thyroid disease can reverse once the thyroid is treated (AAD). Hair grows slowly, though, and shed hairs have to be replaced by new ones starting from the root, so improvement usually takes months rather than weeks.

Step by step

What recovery usually looks like

1. 1Diagnosis and treatment.Your clinician confirms the thyroid problem and starts treatment, then rechecks your levels.
2. 2Levels settle.Shedding may continue for a while, because hairs that were already in the resting phase still fall out.
3. 3New growth.Short new hairs appear, often first noticed along the part or hairline.
4. 4Fullness returns gradually.After shedding stops, hair tends to regain its fullness over about six to nine months (AAD).

If your thyroid is well controlled and your part keeps widening, it's worth looking at female pattern hair loss as a second, separate cause. That's common in midlife, and it responds to its own treatments.

Treatment options when thinning continues

The first step is always to treat the thyroid problem and correct anything else that turns up, such as low iron. If thinning persists, these options have the most evidence for female pattern hair loss:

• Topical minoxidil. The best-studied option. A Cochrane review of 47 trials found evidence that topical minoxidil helps female pattern hair loss compared with placebo (van Zuuren 2016). It takes months of daily use to judge. See our guide to minoxidil for women.
• Prescription options. Clinicians may also consider off-label treatments such as low-dose oral minoxidil or spironolactone, or a compounded topical serum that combines several actives. These need a clinician's review of your health history, medicines and blood pressure.
• Gentle hair care. Avoiding tight styles, harsh chemical treatments and high heat won't fix thinning, but it reduces breakage while hair recovers.

Our guide to hair thinning treatment for women compares these options in more detail.

One prescription option is MAYN, a compounded topical serum that combines minoxidil, spironolactone, tretinoin and other actives in one daily application. A licensed clinician reviews your online assessment and decides whether it's appropriate. It's prescribed off-label, isn't FDA-approved, and some of its ingredients aren't safe during pregnancy or breastfeeding. It isn't a treatment for thyroid disease, so any thyroid problem still needs its own care.

When to see a doctor

Book an appointment if:

• You're shedding much more than usual for several weeks, or your part or ponytail is visibly thinner.
• Hair loss comes with fatigue, feeling cold or hot, a racing heart, weight change or period changes.
• You have round bald patches, scalp redness, scaling or pain.
• You already take thyroid medicine and your hair is still thinning after your levels are back in range.

Swelling in the neck, trouble swallowing, or a very fast or irregular heartbeat should be checked promptly.