Disposable nappies could be the cause of the sharp rise in male infertility over the past 25 years, according to an authoritative scientific study to be published this week. It is thought that disposable nappies heat up baby boys' testicles to such a degree that it stops them developing normally.
Nappies lined with plastic raise the temperature of the scrotum far above body temperature and can lead to a total breakdown of normal cooling mechanisms, according to the study, in the Archives of Disease in Childhood. Doctors in Kiel, Germany, started the study after being alarmed at the temperature of the testicles of infant boys who were brought into hospital with an infection.
The cells supporting sperm production are laid down in the first two years of life. However, their development and sperm production in later life is very dependent on temperature. Testicles need to be cooler than the rest of the body, which is why they are external.
Boys whose testicles descend too late in adolescence are often infertile because they have been kept warm for too long. In adults, exposure to high temperatures, during a fever or while in a sauna, can dramatically reduce sperm count. Tight jeans can also lead to higher testicular temperatures, possibly causing a reduction in sperm count.
Wolfgang Sippell, professor of paediatrics at the University of Kiel, monitored the scrotal temperature of 48 healthy boys, from birth up to the age of four years, using a tiny thermal probe. His team tested the temperatures when boys wore disposable nappies and when they wore re-usable cotton nappies, both during waking and sleeping hours.
The temperature was consistently higher - up to one degree Centigrade above body temperature - when the disposable nappies were worn, with the highest temperatures recorded in the youngest babies. Scrotal temperatures were the same as rectal temperatures when cotton nappies were worn, but far higher when disposable nappies were worn.
They concluded that the insulation properties of the disposable nappies impaired the normal cooling mechanisms of the testicles. They found that, in 13 boys, the cooling mechanism failed altogether.
Sippell concluded: 'A prolonged increase in scrotal temperature in early childhood may have an important role in subsequent testicular health and function, with implications for male fertility.'
Ieuan Hughes, professor of paediatrics at Cambridge University, has examined the research and said it was a cause for concern: 'The testis in the first year of life is a very active organ - the cells to produce sperm are laid down in that time. They could be damaged by high temperatures.'
Repeated studies have shown that average sperm counts have fallen by almost half from 1938 levels and are continuing to decline as fast as 2 per cent a year. The number of British couples seeking treatment for infertility problems has increased by 55 per cent in the past five years and now stands at 27,000 per year. Gina Purrmann, founder of the Real Nappy Association, said: 'Disposable nappies can be very warm, sweaty and itchy. It's another good reason to use cloth nappies. There must be more research so we know for sure.'
However, the Absorbent Hygiene Products Manufacturers Association, which represents makers of disposable nappies, said the study had dubious methodology.
Its spokesman, Peter Stephenson, said: 'There is no evidence to support the assertions made by this study, which would appear to be implausible. The safety of our products is of paramount importance. Disposable nappies are, and remain, safe'.
Dr Louise Parker, reader in paediatric epidemiology at the University of Newcastle upon Tyne, also questioned the study: 'Any speculation that disposable nappies may have played a role in the increase in testicular cancer or decreased sperm count in recent years is completely inappropriate.'
Previously cited causes of the drop in male fertility include the rise of oestrogen in the water supply, widespread use of the contraceptive pill, and hormone-mimicking chemicals in food packaging.