Cretinism is the severe developmental disorder caused by long-term iodine deficiency, usually beginning before birth or in early infancy. Because iodine is the essential building block of the thyroid hormones thyroxine and triiodothyronine, a shortage leaves the body unable to produce enough of them, and the thyroid’s under-activity — hypothyroidism — disrupts the growth of the brain and the skeleton. Children affected show stunted growth, a characteristic broad face and thickened tongue, and irreversible impairment of mental development. In adults, the same deficiency produces goitre and sluggish metabolism. Public-health nutrition treats cretinism as entirely preventable: universal salt iodisation programmes have driven it down wherever they are enforced. Food policy therefore views iodised salt as one of the simplest and most effective fortification measures ever introduced.