If you have a hard time hearing conversation at a bar, it may not be because of the noise, a study suggests.

Alcohol, UK researchers found, seems to temporarily drain a person's hearing -- particularly when it comes to discerning the sounds of conversation.

In a study of 30 healthy volunteers, they found that as participants drank, their hearing became less acute. Lower-frequency hearing, which is necessary for discerning speech, suffered the most, the researchers report in the online journal BMC Ear, Nose and Throat Disorders.

It's a "well observed phenomenon" that alcohol seems to build people's tolerance to loud noise, according to the study authors, led by Tahwinder Upile of the University College London Hospitals.

But bouts of so-called "cocktail party deafness" may not result from the noisy drinking environment alone, the researchers note.

To study the short-term effects of alcohol on hearing, Upile's team recruited healthy adults between the ages of 20 and 40 who had no history of hearing problems. The volunteers had their hearing tested before and after having a predetermined number of drinks in the research lab.

In general, the researchers found, the higher a volunteer's alcohol level -- as measured by breath test -- the greater the deterioration in hearing. The hearing loss tended to be more significant in relatively older volunteers, as well as those who said they had a history of heavy drinking.

It's not clear why drinking may have this effect, but alcohol could either damage the auditory nerves or affect the brain's processing of sound, according to Upile's team.

In this study, the hearing loss was short-lived. Volunteers who returned for tests the following week were back to their normal hearing levels. However, it's possible that regular drinking could alter people's hearing over time, the researchers note.

"There remains a huge scope for further research," they conclude.