In Hong Kong, Lynyrd Skynyrd fans are loving the latest research to come from Hong Kong Baptist University that says human skin flakes are responsible for the bad smell in air-conditioning systems. Skin squames are a source of food for the bacteria found in air-cooling units, which produce odors even in a dust-free air-conditioning system. This research is the first to show that the accumulation and bacterial degradation of skin squames in air-cooling units is positively correlated to the complaints of urine-like smell in air-conditioned areas.
The study found that skin squames shed from the human body can contribute to ammonia (urine-like smell) and volatile fatty acid (body odor) production by bacteria colonising air-cooling units. Skin squames consist of keratins which are structural proteins that can be degraded by keratinase, enzymes produced by some bacteria. The released protein-based fuel source is then consumed by bacteria and broken down to ammonium. With limited amounts of carbon available in the environment, it can lead to excessive amounts of ammonium being emitted into the air and lead to urine-like smell.