A health worker shows the proper way to use a condom as it evokes laughter from the crowd during the celebration of World Population Day in Manilla in July 2009. (Pat Roque/Associated Press)

Nearly half of men surveyed said they had used a poorly fitting condom in the previous three months, according to a new study that sheds light on why couples fail to use them.

The study, published online in February in the journal Sexually Transmitted Infections, was based on a survey of 426 men aged 19 to 67.

Nearly 45 per cent said they had used a condom that fit poorly the last time they had sex during the previous three months.

These men were 2.6 times more likely to say the condom broke, and 2.7 times more likely to say the condom slipped compared with those who said the condoms fit well, Dr. Richard Crosby of the University of Kentucky and Dr. Bill Yarber of the Kinsey Institute for Research in Sex, Gender and Reproduction in Bloomington, Ind., reported.

"Men and their female sex partners may benefit from public health efforts designed to promote the improved fit of condoms," the researchers wrote.

Men often won't buy condoms sized small or medium, the researchers noted. Yarber suggested that condom manufacturers label boxes as medium, large and extra large instead.

The findings have implications for programs trying to encourage condoms to reduce the risk of sexually transmitted infection, including AIDS, as well as unwanted pregnancy, Yarber said in a journal podcast.

Men who said they wore poorly fitting condoms often said it was irritating to wear.

Participants who wore poorly fitting condoms were about twice as likely to say the condoms made it difficult for them, their partners or both to reach orgasm.

Yarber encouraged men to experiment to find a good fit.

"The increased likelihood that men using ill-fitting condoms will remove condoms before sex ends constitutes another form of condom failure," the researchers concluded. "Fortunately, it seems likely that these problems could be rectified through education programs."

It will take some creativity to overcome the emotional barriers to using condoms in both heterosexual and homosexual relationships, Yarber told the journal.

Participants were surveyed through the website of the Kinsey Institute for Research in Sex, Gender and Reproduction.