Condoms that do not fit properly can raise the risk that people will become infected during sex, according to recent US research.

By polling 436 men, the researchers showed that a great number of men feel that condoms do not fit them.

The finding helps explain why condoms are an unpopular preventive measure in African countries where HIV is widespread.

Condoms that do not fit reduce sexual pleasure and ultimately encourage people not to use them at all.

Study authors Richard Crosby of the University of Kentucky and Bill Yarber of the Kinsey Institute for Research in Sex, Gender and Reproduction said that people would benefit from public health efforts promoting the improved condoms that fit better.

Almost half of the people the researchers polled said that they had used a badly-fitting condom during the last three months.

Men who felt their condoms did not fit them were up to 2.5 times as likely to experience the condom breaking or slipping off.

Men who used condoms that did not fit were also much more likely to take them off before they had finished having sex.

The researchers said that, while the right fit may sometimes be available on store shelves, men do not often want to buy condoms that were labeled 'small' or 'medium'.

Simon Blake, from the advisory charity Brook, said that there are many different types of condoms available in different shapes and sizes, and that it takes time to find the right brand.

Natika Halil, from sexual health charity FPA, said that not using the right size was one of the main reasons why men had trouble with condoms.

Gill Gordon, from the International HIV/AIDS Alliance, who has spent time talking to men in Africa about condoms, said that she thought that the unwillingness of African men to use condoms had been overstated, and that many more would be willing to wear condoms designed for greater comfort.