Sunscreen and cosmetics could be killing men's sperm, according to researchers who found that only one in four males has good fertility levels.
Experts in reproduction said chemicals and the trappings of modern life appeared to be damaging men's chances of having a family.
Research found that just 25pc of young men were producing good quality sperm, and the average volume had declined by a quarter since the 1940s.
The findings, presented at the European Society of Human Reproduction and Embryology's annual meeting in Lisbon, prompted warnings from doctors that consumer lifestyles may have created a toxic environment for men.
Dr Niels Jorgensen, a consultant at the Department of Growth and Reproduction at Rigshospitalet, in Copenhagen, said thousands of chemicals found in bathrooms and kitchens were likely to be to blame for the changes. "Modern life is having an impact because we are exposed to so many chemicals and we don't know what they do," he said. Chemicals found in sun cream, cosmetics, frying pans, cars, foods and even in items of clothing could all increase risks to sperm, he suggested. His 15-year study of almost 5,000 Danish men, with an average age of 19, found that 15pc had very poor quality sperm, which meant they were likely to need some sort of fertility help.
A further 27pc could expect a prolonged wait to father children. Just 25pc had good quality semen, while the remainder had a lower standard.
Dr Jorgensen said there was growing evidence from animal studies to suggest that many chemicals disrupt and inhibit the production of testosterone. He expressed particular concern about lotions such as sunscreen.
"We are advised to protect ourselves with these sunblocks but it seems when you go to the laboratory and test some of these chemicals they can interfere with the sperm function," he said.
"If I was to advise my own family I would say don't use it." Prof Richard Sharpe, of the MRC Centre for Reproductive Health at Edinburgh University, said he did not believe that chemicals were behind the drop in sperm counts, but said more research was needed to establish the reason.
Dr Chris Flower, of the Cosmetic Toiletry and Perfumery Association, said: "We can state categorically that cosmetic products are required by strict European laws to be safe.
"The industry and the regulators are aware of concerns regarding possible endocrine effects and if such a risk was present from cosmetic products, action would already have taken place to deal with it."
Meanwhile, Finland's health ministry has advised Fins to eat their meals standing up from time to time in a bid to combat health problems linked to a sedentary lifestyle. In a new publication called 'Sit Less, Feel Better', the ministry said.
"Many things can be done in a standing position or walking around instead of sitting down.
"Standing up also works for reading a newspaper, eating, taking a coffee break and watching television."