Hair Loss and Thyroid Disorders
"Abnormal hormones are often blamed for loss of scalp hair though, perhaps surprisingly, they are responsible for just a small minority of instances of this distressing symptom. Many different conditions can lead to hair loss; some hair loss is part of normal life. Women after childbirth and at the time of the menopause can lose hair and almost every man will lose some hair by the time of reaching adulthood. Elderly males and females will develop baldness of various degrees, which is largely determined by genetic factors.
Human scalp hair does not grow continuously. Every hair follicle (the unit of hair production) undergoes phases of growth, during which hair lengthens, followed by a period of rest (the telogen phase). During telogen, the hair is shed and replaced by a new hair. In some animals this process is synchronised; that is why dogs lose a lot of hair at the same time or "moult". Human hair growth is not coordinated in the same way, so at any one time different hair follicles are at different stages of their growth cycle. So, it is normal to have some ongoing continuous hair loss, which usually is balanced by new hair growth. One of the commonest causes of hair loss is called "telogen effluvium". This can be triggered by any severe illness, for instance pneumonia or a major operation. The stress of the illness causes all hair follicles to go into their resting phase and hair growth temporarily ceases. Because the human hair cycle is long (several months), the hair loss may not become apparent for several months, by which time the person will have recovered from their illness. Such hair loss also coincides with new hair beginning to regrow and therefore the hair loss is transient.
Hair loss and thyroid disease
Severe and prolonged hypothyroidism and hyperthyroidism can cause loss of hair. The loss is diffuse and involves the entire scalp rather than discrete areas. The hair appears uniformly sparse. Regrowth is usual with successful treatment of the thyroid disorder, though it will take several months and may be incomplete. It is unusual for mild (e.g. subclinical) hypothyroidism or hyperthyroidism, or short-lived thyroid problems to cause hair loss.
Some forms of hypothyroidism and hyperthyroidism come on abruptly and are diagnosed early, while others may have been present for months or years before diagnosis. Hair loss due to thyroid disease becomes apparent several months after the onset of thyroid disease. This is due to the long hair cycle. In such cases, paradoxically the hair loss may follow the treatment for the thyroid and the thyroid medication may be erroneously blamed, leading to withdrawal of treatment, which in turn may worsen the hair loss.
Hair loss and anti-thyroid treatment
Anti-thyroid drugs (carbimazole and propylthiouracil) can, in rare cases, cause diffuse hair loss. It may be very difficult to tell whether the hair loss is due to the effects of the previous overactivity of the thyroid or the anti-thyroid drugs. In all probability the anti-thyroid drugs are not the cause and it is unusual to have to seek alternative treatment for hyperthyroidism. Radioiodine does not cause hair loss.
Hair loss associated with autoimmune thyroid disease
Most people with hypo- or hyper-thyroidism have autoimmune thyroid disease. If a person has one autoimmune disease he/she is more likely than others to develop some other autoimmune condition. Alopecia areata is an autoimmune condition that causes hair loss that occurs in people with autoimmune thyroid disease more often than expected by chance. Unlike the types of diffuse hair loss described above, alopecia areata causes discrete, often circular, areas of hair loss. In most cases this is transient and does not progress, but unfortunately it can cause significant baldness. There are other rare autoimmune conditions that can cause hair loss through scarring (e.g. lupus erythematosus), which are associated with autoimmune thyroid diseases. Polycystic ovarian syndrome is also associated with autoimmune thyroid disease and may manifest as diffuse hair loss; other features are irregular periods, obesity and acne.
Investigations for hair loss
If you are experiencing hair loss and it is enough to cause concern, you should seek advice from your GP. It is unusual for thyroid disease to cause hair loss without other symptoms of an over- or underactive thyroid. Your doctor will decide if it is appropriate for you to have additional tests to exclude other causes of diffuse hair loss such as iron deficiency. There are also rarer causes of hair loss, which your GP may feel are worth excluding. Sometimes referral to a skin specialist is required in order to make an accurate diagnosis. "
Authors: Petros Perros, John Hunter, Mark Strachan for Thyroid Foundation
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