Women have been warned to be careful about using bug spray while pregnant after a study linked the use of insect repellent to an increasingly common birth defect in boys.

Hypospadias is a condition where the opening of a boy’s urethra appears in the wrong place on the penis, usually on the underside rather than the tip.

It generally requires surgery.

It is estimated to affect about one in every 500 boys and seems to be on the increase, leading researchers to look at whether some chemicals in commonly used products are a contributing factor.