Chemicals in common household products such as toothpaste, soap and plastic toys have a direct impact on human sperm which could help explain rising levels of male infertility, scientists have found.

One in three “non-toxic” chemicals used in the manufacture of everyday items significantly affected the potency of sperm cells, according to the Independent. This may account for the high incidence of unexplained infertility in the human population, the researchers said.

It is the first time that a study has found a direct effect of the many ubiquitous man made chemicals in the environment on a vital function of human sperm. The findings will raise further concerns about the hidden toxicity of chemicals deemed safe by toxicology tests.

But the researchers believe they have developed a new way of testing the impact of household chemicals on human sperm which will allow regulatory authorities in Europe to decide whether to ban or impose restrictions on their use in certain products.

The study was part of wider research into so-called “endocrine disrupting” chemicals that for several years have been linked with declining sperm counts and widespread male infertility.

In some cases, these chemicals are thought to mimic female sex hormones – oestrogens – and in other cases act as anti-androgens, the male sex hormones, thereby interfering with the male reproductive system.

However, the scientists found that one in three common household chemicals found in products such as sun screens, detergents and plastics directly sabotaged the human sperm’s swimming behaviour and caused them to prematurely release the critical enzymes needed to penetrate and fertilise the egg cell – which would render the sperm infertile.

They also found that the concentrations needed to trigger these adverse reactions were similar to the very low levels commonly found within the human body. In addition, they showed for the first time that there was a “cocktail effect”, when a number of chemicals worked together to amplify their individual effects.

“For the first time, we have shown a direct link between exposure to endocrine-disrupting chemicals from industrial products and adverse effects on human sperm function,” Professor Niels Skakkebaek, of Copenhagen University Hospital in Denmark, said.