Four in ten worry about friends putting uncomplimentary photos of them on the site, with women concerned about it more often than men, the Daily Mail reported.
The figures were revealed by a survey for shopping site VoucherCodes.co.uk.
Its co-founder, Duncan Jennings, dubbed the trend "virtual vanity."
A fifth of Facebook users regularly exaggerate posts on their page to make their lives appear more exciting
A quarter of the 2,000 people aged between 18 and 25 who were interviewed for the survey, admitted that they felt low and unpopular when they saw friends talking about social events to which they had not been invited.
A further 25 percent were so worried about their appearance on the site that they regularly splashed out on new clothes to avoid being photographed in the same outfit twice.
The poll also revealed that young Britons spent an average of one hour and 20 minutes a day on Facebook, but nearly ten percent used it for more than eight hours daily - the equivalent of a full working day.
A fifth of users were so concerned about their online appearance that they regularly exaggerated posts on their page to make their lives appear more exciting.
"Facebook is an integral part of young people's lives but it's putting pressure on them to fit in and look the part, which is especially challenging for groups such as cash-strapped students," Jennings said.