But the failure of politicians, teachers and often parents to acknowledge these physical and emotional changes only adds to teenagers' stress and leads to poor physical and mental health among this age group, they say.

The authors from Liverpool John Moores University Centre for Public Health, say that the onset of puberty has been steadily falling for the past 150 years, and has dropped three years within the past century alone, as a result of public health measures and improved nutrition.

But it is also due to stress, with parental separation/divorce and absentee fathers "one of the most effective stressors," they write. Rates of divorce and single parenthood have rapidly increased in many countries, they say.

But despite the younger age at which children reach puberty, there have been no attempts to develop young people faster, "leaving an increasing gap between physical puberty [changes to their bodies] and social puberty [when they are able to make decisions for themselves]," they write.

"The results can be ill informed health damaging behaviour," they say, including unprotected sex, substance abuse, self harm, violence and bullying, with disadvantaged communities likely to hit the hardest.

While society in general might prefer to ignore earlier puberty, the commercial sector certainly has not, drawing heavily on sexual imagery in their marketing to young teens, say the authors.

"Such marketing is more likely to reinforce the confusion caused by separated physical and social puberty rather than providing the information necessary to deal with it," they write.

"In the short term, responding to earlier puberty means moving away from societal attitudes that equate protecting children with regarding them as firmly ensconced in childhood long after their physical journey into adulthood has begun," contend the authors.

"Such pretence, however well intentioned, simply denies them the vital information they require to complete this transition without damaging their health," they conclude.

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