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Thyroid and hair
The thyroid gland controls the speed of metabolism in almost all tissues, including the skin and the hair follicles. That is why disorders of its function are often noticed on the hair first, sometimes even before other, more obvious symptoms appear.
How thyroid hormones affect hair
A hair follicle does not grow continuously. It goes through cycles: the anagen growth phase, a short transitional catagen phase and the telogen resting phase, after which the hair falls out and makes room for a new one. At any moment most follicles on the head are in the growth phase.
Thyroid hormones, T3 and T4, directly affect the duration of those phases. When their level is disturbed, a larger number of follicles move into the telogen phase prematurely. The result is diffuse shedding: the hair thins evenly across the whole head, not in a pattern as in androgenetic alopecia.
Why the shedding is noticed with a delay
A hair that enters the telogen phase does not fall out immediately. It stays in the follicle for another two to three months. That is why increased shedding only becomes visible several months after the hormonal disorder started. The same applies in the opposite direction: when the gland’s function is regulated, the improvement is not seen immediately but with a similar delay.
Hypothyroidism, an underactive gland
With reduced thyroid function metabolism slows down. The symptoms most often listed in the specialist literature include:
- Fatigue and a drop in energy that rest does not resolve
- Sensitivity to cold
- Weight gain without a change in diet
- Dry skin and dry, brittle hair
- Diffuse hair shedding
- Constipation
- Puffiness, particularly around the eyes
- Slowness, difficulty concentrating, low mood
- Irregular or heavier periods
In more pronounced hypothyroidism, thinning of the outer third of the eyebrows is sometimes described. It is a frequently mentioned finding, but it is neither obligatory nor specific: it can occur for other reasons too.
Hyperthyroidism, an overactive gland
With increased function the picture is largely the reverse:
- Nervousness, irritability, restlessness
- A fast heartbeat and a feeling of palpitations
- Weight loss despite a normal or increased appetite
- Sensitivity to heat and increased sweating
- Trembling hands
- Insomnia
- More frequent bowel movements
- Hair that becomes thin, soft and brittle
Both hypothyroidism and hyperthyroidism can cause diffuse hair shedding. The appearance of the shedding itself does not say which disorder it is: only the laboratory result shows that.
What is tested
The basic screening test is TSH, the pituitary hormone that regulates the thyroid. If needed it is supplemented with free T4 and T3, and where autoimmune disease is suspected also with antibodies, anti-TPO and anti-Tg. In Hashimoto’s thyroiditis and Graves’ disease antibodies are often elevated.
In addition, at the doctor’s discretion, an ultrasound of the gland is performed. Interpreting all these results belongs to an endocrinologist or the treating doctor; values are considered together, in the context of symptoms, not individually.
When to see a doctor
If, along with hair shedding, there is also a cluster of symptoms from the lists above, particularly persistent fatigue, unexplained weight change, marked sensitivity to cold or heat, changes in heart rhythm or the menstrual cycle, a conversation with a doctor and basic tests are a sensible first step. The same applies if there is a family history of thyroid disease.
What happens to the hair after treatment
When the gland’s function stabilises with appropriate treatment, the follicle cycle usually returns gradually to normal. In this type of shedding the follicles are as a rule not destroyed: they were temporarily pushed into a resting phase. Recovery is slow and is measured in months, not weeks, and it is usual to first notice new, short hair along the hairline.
The following is also important: if the cause of the shedding is hormonal, the solution lies in regulating the hormones. No cosmetic product can replace that treatment or affect thyroid function. Hair care, serums and ampoules, mild shampoos, careful handling, acts on the scalp and the hair and makes sense as support, not as a solution to the cause.
Hair care during recovery
While the condition is being treated, hair is often drier and more brittle than usual. A few practical things reduce additional damage:
- A milder shampoo and regular use of conditioner on the lengths
- Less heat, a lower hairdryer temperature, less frequent use of straighteners
- Avoiding tight hairstyles that mechanically strain the root
- Postponing chemical treatments until the condition stabilises
- Combing from the ends towards the root
In short
- Thyroid hormones regulate the hair growth cycle; a disorder pushes follicles into the resting phase.
- The shedding is diffuse, across the whole head, and lags two to three months behind the cause.
- Both reduced and increased function can cause hair shedding.
- The diagnosis is made in the laboratory: TSH, T4, T3 and, if needed, antibodies.
- After function is regulated the hair usually recovers gradually.
- Cosmetics do not affect thyroid function and do not replace treatment.
This text is informative in character and does not constitute medical advice or a basis for self-diagnosis. For interpretation of symptoms and results consult a doctor.