Parents often think their children grow up too quickly, but few are prepared for the problem that Michael Dedekian and his colleagues at the University of Massachusetts Medical School reported recently.

At the annual Pediatric Academic Society meeting in May in San Francisco, they presented a report that described how a preschool-age girl, and then her kindergarten-age brother, mysteriously began growing pubic hair. These cases were not isolated; in 2004, pediatric endocrinologists from San Diego reported a similar cluster of five children.

It turns out that there have been clusters of cases in which children have prematurely developed signs of puberty, outbreaks similar to epidemics of influenza or environmental poisonings. In 1979, the medical journal the Lancet described an outbreak of breast enlargement among hundreds of Italian schoolchildren, probably caused by estrogen contamination of beef and poultry.

Increasingly though the science is still far from definitive and the precise number of such cases is highly speculative some physicians worry that children are at higher risk of early puberty as a result of the increasing prevalence of certain drugs, cosmetics and environmental contaminants, called "endocrine disruptors," that can cause breast growth, pubic hair development and other symptoms of puberty.

Most commonly, outbreaks of puberty in children are traced to accidental drug exposures from products that are used incorrectly. Dedekian's first patient was evaluated for possible genetic endocrine problems and a rare brain tumour before the cause of her puberty was discovered. It turned out that her testosterone level was almost 100 times normal, in the range of an adult man.