The decline in male fertility continues to accelerate. But the cause remained largely unknown. Now researchers believe they have an insight into what damage is being done to sperm, and by what.

The concentration of active sperm in male semen has collapsed by more than 50 per cent over the past 50 years. And that decline has only accelerated since the turn of the century.

About one in six couples experience infertility problems.

It impacts men and women equally. But, in 30 per cent of all cases, no cause can be found.

This has been the subject of thousands of studies worldwide. But no definitive answer has yet been found.