Declining sperm quality: a review of facts and hypotheses

A substantial body of evidence has accumulated in recent years suggesting that human semen quality may be deteriorating. This has been associated with evidence of other changes in male reproductive health, including increases in congenital malformations and testis cancer in men, and associated problems in wildlife. Unfortunately the evidence remains inconclusive. It has been suggested that these changes may be due to environmental xenoestrogens acting during development. Although there is now a large quantity of data indicating that this is a plausible hypothesis, evidence of causality, rather than association, remains to be provided. The potential importance of these changes for human health is considerable, and urgent research is required to clarify the situation.