Scientists and technicians who work with animals in ill-equipped laboratories run the risk of developing asthma.
Exposure to high levels of airborne rat urine allergens has been identified as a key contributor to cases of occupational asthma that blight the lives of one in 20 lab animal workers. The length of exposure was found to be far less significant.
Sufferers cough, wheeze and have a shortness of breath when they subsequently come into even low-level contact with the animals. Many are forced to switch jobs and some are unable to work again.
The study, by Mark Nieuwenhuijsen, senior lecturer in environmental epidemiology, and colleagues at Imperial College London, has highlighted the importance of improving working conditions for researchers who work with animals.
Thirteen improvement notices were issued to UK laboratories after visits last year by Health and Safety Executive inspectors found unacceptable levels of exposure to animal allergens.
The HSE has targeted the problem as part of a bid to cut levels of occupational asthma by 30 per cent by 2010. The disease can be caused by breathing in rat urinary aeroallergen (RUA).
Dr Nieuwenhuijsen's team studied a group of 342 laboratory animal workers in two UK research establishments over four years. Their results will be published in the journal Occupational Environmental Medicine .
People in the highest exposure category, typically animal technicians who were exposed to up to 30 micrograms of RUA per metre cubed, were four times more likely to develop asthma than those in the lowest exposure category.
Up to 30,000 people work with or come into contact with lab animals in the UK each year.
Dr Nieuwenhuijsen said the risk could be reduced to an acceptable level. Rooms could be better ventilated, and cages designed to completely isolate the animals from the humans could be used.