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Human skin to blame for urine-like smells in air conditioning, say researchers

Researchers in Hong Kong find that cells from the skin surface will create food for bacteria, creating odour even in dust-free environments

Research by Hong Kong Baptist University has conclusively proved that skin causes odours in air conditioning.   Dr Lai Ka-man, Associate Professor of the Department of Biology of HKBU led a study that found skin squames - cells that peel from the skin - can be broken down by the bacteria in air conditioning units to produce ammonia, creating urine-like smells in air conditioned rooms, The research also found that the combination could also produce volatile fatty acids, giving rise to a body odour-like smell.

The researchers believe the findings challenge the prevailing wisdom that odour problems are due to a ’dirty’ air-conditioning system due to accumulated dust, harbouring microbes and that cleaning the system repeatedly will eliminate the odour. The study found that odour was sometimes reported from ’clean’ systems without visible dust accumulation, and that cleaning the system repeatedly doesn’t prevent the problem recurring.

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 ammonia. With limited amounts of carbon available in the environment, it can lead to excessive amounts of ammonia being emitted into the air and lead to urine-like smells. 

Dr Lai recommended increased filtration for effective long-term odour control. She said: ”The simplest way is to install an appropriate filter to capture the skin squames in the air. The size of skin squames is generally larger than 10 micrometres (or 0.001 centimetres). A filter that can effectively capture particles less than this size should help improve the odour problem.”




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