Diapers lined with plastic significantly increase the temperature of the scrotum - the testicular sac - in boys, shows the research from Kiel, Germany. Temperature is critical to normal testicular development and sperm health.
The research team monitored the scrotal temperature of 48 healthy boys, including five premature babies, from birth up to the age of 4.5 years, using a tiny thermal probe.
The study ranged over two 24-hour periods: during one the boys wore re-usable cotton diapers; during the other, they wore plastic-lined disposable diapers. Temperature was measured during waking and sleeping hours; and rectal temperature was also measured for comparison.
Testes' temperature significantly higher - up to 1°C above body temperature - with disposable diapers.
Temperature was consistently and significantly higher - up to 1°C above body temperature when the disposable diapers were worn.
The highest temperatures were recorded in the youngest babies. Rectal temperatures were significantly lower than scrotal temperatures when the children wore disposable diapers, but were the same when cotton diapers were worn.
This, says the authors, shows that the insulation properties of the disposable diapers impaired normal testicular cooling mechanisms. In 13 boys, the cooling mechanism failed altogether.
In adults the evidence shows that exposure to high temperatures - for example, during episodes of fever or while in a sauna - can reduce sperm count, and has been used as a form of contraception in men.
The subsequent risk of adult infertility in boys whose testicles fail to descend at the normal age is thought to be attributable to increased testicular temperature.
A prolonged increase in scrotal temperature in early childhood may therefore have an important role in subsequent testicular health and function, with implications for male fertility.