Once the "distractor faces" were introduced, the attractiveness of the original faces increased from the first round of ranking, the researchers discovered.
Dr Nicholas Furl, who conducted the study, said: "Until now, it's been understood that a person's level of attractiveness is generally steady.
"If you saw a picture of George Clooney today, you would rate him as good-looking as you would tomorrow.
"However, this work demonstrates that the company we keep has an effect on how attractive we appear to others."
In a further limb to the study, the team also discovered that having a less attractive face to look at sharpened viewers' critical faculties and made them more sensitive to the differences between two or more attractive people.
"The presence of a less attractive face does not just increase the attractiveness of a single person, but in crowds could actually make us even more choosy," said Dr Furl.
"We found that the presence of a distractor face makes differences between attractive people more obvious and that observers start to pull apart these differences, making them even more particular in their judgment."
The new research lends empirical weight to a theme often exploited for comic effect.
Last year's film The Duff - an acronym for "Designated Ugly Fat Friend" - told the story of a school-age girl who finds out that her prettier and more popular friends have deliberately recruited her to elevate their own desirability.
"It's perhaps not too surprising that we are judged in relation to those around us," said Dr Furl.
"There are many other ways in which we decide who we are attracted to.
"There will certainly be more research in years to come on this complicated area of human interaction, and I am excited to see where this research takes us."
The new research follows previous investigation into the effect on perceived attractiveness of appearing alongside people of the opposite sex, which found that married men are generally thought of as more attractive than bachelors.
This is thought to occur because people appear more attractive when they are in the company of an attractive person, or people, of the opposite sex - the so-called "Hugh Hefner effect", after the owner of Playboy magazine who is often picture arm in arm-in-arm with several of his girlfriends.
Scientists believe the phenomenon could be explained by evolution, as, in the animal kingdom, male creatures with more mates are often considered genetically superior.
Experiments with grouse in the 1990s found that researchers were able to boost the popularity of a male simply by placing models of female birds around it.
