Researchers have found that everyday chemicals present in the environment can reduce male fertility. Some substances affect the ability of sperm to penetrate an egg, because they cause the sperm to prematurely release chemicals that help it to break down the egg's outer layer.

A study has shown that chemicals found in industrial and domestic products and even ordinary foodstuffs can act like female hormones and affect male fertility. Lynn Fraser, professor of reproductive biology at King's College, London, said that these substances, known as environmental oestrogens could directly affect the normal functions of sperm cells. Speaking at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE) last week, she said 'given that environmental oestrogens are very potent and that we are probably being exposed to several at the same time, it is important to know whether they have cumulative effects'.

Another study presented at ESHRE has shown that men who smoke may decrease their chances of fathering a child through IVF or ICSI (intracytoplasmic sperm injection). Dr Michael Zitzmann, from the Institute of Reproductive Medicine in Munster, Germany, said that the DNA of sperm was altered by smoking and that this may inhibit embryo development.

Zitzmann's team studied 301 couples - 148 were undergoing IVF and 153 were using ICSI. In the respective groups, 68 and 71 men were smokers. In the IVF group, 18 per cent of the women with smoking partners became pregnant compared to 38 per cent of women with non-smoking partners. Similar results were shown in the ICSI patients. Zitzmann said that the 'chances of the whole procedure failing and no pregnancy occurring was two to three times higher in smoking men compared with non-smokers'.