Hyperthyroidism occurs when the thyroid becomes over-active and produces more thyroid hormones than are needed by the body. It is sometimes called thyrotoxicosis. The most common cause of hyperthyroidism is Graves’ disease. Hyperthyroidism is also one of the phases that can occur in a condition called viral thyroiditis, although this is extremely rare in children. The hyperthyroid phase of viral thyroiditis normally settles down without treatment.

Graves’ disease

Graves’ disease is the most common form of hyperthyroidism. It is named after the Irish physician who first recognised it in the 19th century. Graves’ disease is caused when the body’s immune system turns against the thyroid gland by producing antibodies. This switches the thyroid gland ‘on’, a bit like flicking on the light switch at home. The thyroid gland becomes over-active and produces too much thyroid hormone.

There may be a family history of thyroid problems or other autoimmune disorders. It is also more common in people who smoke.

How common is it?

Around 100 children under 15 get Graves’ disease in the UK and Ireland each year. Girls are more likely to develop it than boys.