A large minority of male condom users complain that ill-fitting prophylactics are liable to split and break during intercourse and be a sexual turnoff, researchers said on Tuesday.
US investigators analysed questionnaires completed by 436 men between the ages of 18 and 67 who had been recruited via ads in newspapers and a blog on the website of a condom sales company.
The volunteers had used condoms for vaginal intercourse in the previous three months.
A remarkable 44.7 percent of the respondents said they had experiences of condoms that were ill-fitting, the doctors found.
Poorly-fitting condoms more than doubled the risk of breakage, slippage, erection loss and difficulty in reaching an orgasm, either by the user or his partner. They were also five times likelier to cause irritation of the penis.
Such problems prompted many users to remove the condom before intercourse ended -- a worrying phenomenon in the fight against unwanted pregnancies and sexually-transmitted disease.
The work is reported online by the journal Sexually Transmitted Infections, published by the British Medical Association (BMA).
The researchers, led by Richard Crosby and Bill Yarber at the Kinsey Institute for Research in Sex, Gender and Reproduction in Indiana, acknowledge that the study may have been limited by self-reported data.
Even so, the evidence highlights some worrying problems about the use of condoms, especially as a barrier to sexual pleasure, which made using it a real deterrent for some.
It also shows the need for "public health messages" to enjoin men to get the right size of condom, they said.
On this point, men -- and condom manufacturers -- will have to deal with the delicate question of penis size, say the authors.
For one thing, widespread pornography may have distorted the male self-image, making it harder for some men to accept that they have a less than gigantic member.
"The old saying is, women don't have penis envy, men do," Yarber said.
Condom makers would be advised to start calling their smallest size "large", and then move on to "extra large" for medium size and so on, he suggested in a podcast (http://podcast.bmj.com/sti).
"Certainly, don't label them as large, medium or extra small," he said wryly.