Men who take steroids or hair loss drugs to improve their appearance are damaging their ability to have children, experts claim.
Scientists have warned that men are harming their fertility out of vanity, having been inspired by image-obsessed programmes such as Love Island.
Millions of people have turned to anabolic steroids to bulk up in an attempt to make themselves more attractive. But the drugs, which mimic the effects of testosterone in the body, can stop men producing any sperm, making them completely infertile - with the effects potentially lasting for longer than a year.
A hair loss drug called finasteride - which claims to reverse baldness - may have a similar effect on men’s fertility.
It has been described as a “fertility paradox” by British experts, who say some men may be trying to look better to attract women because, on an unconscious biological level, they want to impregnate them. But the result of the drugs could be that some men end up unable to do so.
Professor Allan Pacey, of the University of Sheffield, published the theory with Dr James Mossman, of Brown University in the US. He said: “Men often don’t realise the effect steroids can have on their fertility. They are just going to the gym and see steroids as a quick way to build muscle and look good. It is being fuelled by reality television programmes like Love Island.
“Hair loss drugs are also taken out of vanity and it is highly ironic that, from an evolutionary point of view, men are doing this to attract women, only to risk their ability to have children with them.”
Steroids, regularly used by bodybuilders but increasingly taken illegally by regular men, help increase muscle by boosting testosterone.
This tricks the pituitary gland into thinking the testes have gone into overdrive, so the brain shuts off two hormones which control sperm production. Finasteride, sold under brand names such as Proscar and Propecia, increases testosterone in the blood by altering the way it is broken down.
Many men are left unable to produce any sperm at all, and forced to have painful surgery to extract it if they want to start a family.
Dr Mossman said: “These men are trying to be big and strong, as muscly as possible so they can be at their evolutionary peak and make themselves more attractive to the opposite sex. They need to realise that taking steroids to achieve this will make them among the least fertile people in the population.”
The ‘Mossman-Pacey fertility paradox’ report is published in the Journal of Internal Medicine.