Causes of Precocious Puberty
Hormones are chemicals produced by specialised endocrine glands. In normal puberty, hormones from an area of the brain called the hypothalamus signal to the pituitary gland (a small gland situated underneath the brain) via a hormone called gonadotrophin-releasing hormone to produce hormones known as gonadotrophins (luteinising hormone and follicle stimulating hormone). These gonadotrophins in turn stimulate the sex glands (gonads: testicles in boys and ovaries in girls) to produce steroid hormones. These hormones are mainly testosterone in boys and oestrogen in girls and it is these steroid hormones that stimulate the development of the physical signs of puberty. In precocious puberty, there can be early activation of nerve cells in the hypothalamus producing gonadotrophin-releasing hormone or excess gonadotrophin production from the pituitary gland as a result of a pituitary tumour. In both cases, the pattern of pubertal development is usually normal, but premature or precocious. 

The cause of precocious puberty related to early increases in activity of the hypothalamus is usually unknown although underlying causes are occasionally found in girls and in up to 50% of boys. The causes may include excess fluid (hydrocephalus) after head trauma or radiotherapy, and benign or malignant brain tumours.

There are other rare forms of early sexual development. Puberty is not always due to premature activation of the hypothalamus or excess gonadotrophin hormone production. These rare forms include early breast development without the development of other secondary sexual characteristics (premature thelarche), an increased production of androgens from the adrenal cortex (adrenarche) causing premature development of pubic and armpit hair and overproduction of testosterone due to a genetic-mutation'>genetic mutation in the signalling of gonadotrophins. McCune Albright syndrome is also associated with precocious puberty, due to an underlying defect in the ovaries or testes.