Precocious or delayed puberty

Puberty describes the phase of human development that leads to sexual and physical maturity. It begins with endocrine changes in the central nervous system.  

At the onset of puberty, there is a pulsatile release of gonadotropin-releasing hormone (GnRH) in the hypothalamus. The production of GnRH subsequently leads to an increased secretion of luteinising hormone (LH) and gonadotropin (follicle-stimulating hormone, FSH), which in turn stimulate the production of oestrogens and androgens in the gonads.  

In girls, puberty usually begins a few years earlier than in boys. With the shift of hormones come multiple physical changes, which typically include a growth spurt and the development of underarm and pubic hair in both sexes. In young males the voice deepens and facial hair begins to grow. Young females experience an increase in fat mass, breast development and the menarche (the first period). 

If these sexual characteristics develop before the age of approximately 9–12 years, this is referred to as precocious puberty. In contrast, if puberty starts after this age range, it is considered delayed.