Conditions in which the mineral content of the body is not properly regulated. There are two forms, hyper- and hypoparathyroidism, over- and underactivity of the glands respectively. The parathyroids are hormone-producing glands, usually four in number, hidden on either side of the thyroid in the neck; their function is to control the level of calcium and phosphates in the body. Underactivity can be caused by the accidental removal of the parathyroids during a thyroid operation. In new-born babies the function of the parathyroids can be inhibited by excessive phosphate content in food (cows’ milk), but in most cases the cause is unknown. Parathyroid hormone deficiency causes excessively low calcium levels in the blood, which can be serious because of the important functions fulfilled by this element. If the level becomes acutely low, nerves and muscles are very easily irritated, causing painful spastic muscular cramps in the limbs and throat (tetany). The latter can cause constriction, and convulsions. In the long run the deficiency leads to listlessness, character changes and haziness of vision caused by calcium deficiency in the lens (cataract). The skin becomes dry and scaly, and hair falls out, particularly the eyebrows, and fungus infections of the skin may set in. In children bodily growth and tooth development are often disturbed.