Shed skin to blame for unpleasant odour from air conditioners, Hong Kong researchers find

People – namely their shed skin – are to blame for the unpleasant odour emanating from air conditioners. But before this tidbit makes your flesh crawl, know that finer filters on the units can prevent the phenomenon, according to a local study released on Wednesday.

Hong Kong Baptist University researchers found that even air conditioners free from dust can harbour bacteria inside them. When the bacteria consume and degrade nutrients in human skin flakes, they release a urine-like odour.

To eliminate the smell effectively, air conditioner filters should be replaced with finer ones that can block particles measuring as little as 10 microns in diameter, so that skin flakes cannot enter the system, according to Lai Ka-man, the lead researcher and a biology professor at the university.

“The size of skin squames is generally larger than 10 microns,” she said of shed human scales. “If you smell a urine-like odour coming from the air conditioner, replacing the filter is the simplest solution.”

Humans naturally shed millions of dead skin cells every day.