Prolonged exposure to baby milk powder increases the risk of breathing problems, including wheezing and breathlessness, a study has found.
Only people who deal with large quantities of powder are at risk
It looked at 170 Thai factory workers who made the powder, but the team from University of Birmingham says the risk could also apply to nannies.
Mothers and babies are safe, because they have relatively little exposure.
But the study, published in the European Respiratory Journal, says at-risk workers should be monitored.
It is already known that consuming milk powder can lead to the development of an allergy if a child has an intolerance to cow's milk but the potential risks of inhaling milk powder have never before been studied.
In this research, a team from the Institute of Occupational and Environmental Medicine at the University of Birmingham and Thailand's Mahidol University looked at just under 170 workers in a Thai baby milk factory.
The factory had high hygiene standards, and concentrations of milk powder dust were relatively low.
The majority - 130 - were directly involved in manufacturing and packaging baby milk. Another 22 were responsible for adding vitamins to the milk and 15 were quality controllers.
The researchers compared these workers' health with that of 76 office workers using a questionnaire and lung function tests.
Twice as many people who worked with milk powder had symptoms, with 24% experiencing wheezing and 33% having breathlessness compared to 12% and 16% of the office workers.
The difference remained even when the researchers took other factors, such as smoking, into account.
Lung function tests also showed a significant reduction in how strongly milk powder workers were able to breathe out.
Those working with the powder were also found to be twice as likely to have had asthma.
The researchers, led by Dr Maritta Jaakkola, say the results suggest the workers are hyper-sensitive to the powder, rather than simply irritated by it.
Dr Jaakkola said: "The effects of inhaled milk powder are relevant for occupational settings, so workers with such exposure should be protected as much as possible using exposure control measures, such as wearing latex gloves.
"They should also have regular check-ups of their respiratory health.
"Nannies, and bakers, both groups who are exposed to milk powder during their working life, may also benefit from respiratory tests."
But Leanne Male, assistant director of research at Asthma UK said the levels of powder a person would need to be exposed to in order to suffer breathing problems would have to be high, and reassured mothers they would not be affected.
Ms Male said the risk was highest for people who manufactured the powder.
She added: "This research highlights the dangers of occupational asthma and the need for employers to recognise potential triggers in the workplace."