The trendy denims are causing twisted testicles, bladder weakness and even urinary tract infections.

Low sperm count and fungal infections are also being put down to the tight-fitting jeans.

Dr Hilary Jones, who is working on a project to highlight the dangers posed by the jeans, said: "I have seen several cases of men who have twisted their testicles due to wearing jeans that are far too tight.

"My advice would be to make sure you leave plenty of room around the groin area and that your trousers feel comfortable so you're not being restricted in any way.

"Men who wear tight or ill-fitting trousers, or underwear that is restrictive around the groin area, could be damaging their health.

"Wearing tight-fitting clothing over a prolonged period can lead to urinary tract infections leading to over-activity of the bladder - a type of bladder weakness - as well as a low sperm count and fungal infections.

"Please don't put style before health."

Twisted testicles occur when tight trousers prevent the spermatic cord from moving freely, meaning it twists and leads to testicular torsion. This cuts off blood supply and requires immediate surgery to prevent a gangrenous testicle.

Tight-fitting jeans around the groin can put additional pressure on the bladder but can also lead to bacteria breeding and re-entering the body causing urinary tract infections.

This creates the need to urinate more frequently and can cause severe pain.

Jones' warning was made as a study of 2000 British men revealed that one in 10 had experienced an unpleasant side effect as a result of wearing skinny jeans.

Of the men suffering from "skinny jean syndrome", half had experienced groin discomfort, more than a quarter had bladder troubles and one in five had a twisted testicle.

One in four of the respondents regularly squeeze into jeans with the most common reason given for enduring tightness being "to show I can still fit into them" and "because they look good".

Three in 10 respondents have been made uncomfortable by tight jeans and 40% of them admit that they sometimes sacrifice comfort for style.

One in seven British men regularly wear skinny jeans but more than a third confess that they don't know their jean size.

Zoe Brimfield, a spokesman for the sponsors of the survey, said: "With this survey we were keen to highlight that, though men might like the look of tight-fitting jeans, it is important that they are not compromising their health.

"Bladder weakness in more common than people think. One in nine men in the UK is experiencing some form of it."