The potential risks of inhaling milk powder, rather than consuming milk proteins, have never been studied specifically. However, an original study undertaken in a Thai baby milk factory by a British team suggests that exposed workers need to be monitored for hypersensitivity to milk powder.

The study, undertaken jointly with Thailand's Mahidol University, covered 167 workers in a baby milk factory. They included 130 workers involved directly in product manufacture and packaging, 22 responsible for adding vitamins to the milk and 15 quality controllers. By way of a control group, 76 office workers employed in this factory or in other Thai plants were also included in the study. A total of 142 men and 101 women were recruited, aged between 18 and 60 years.

All of the participants were asked to complete a health questionnaire on respiratory, nasal, eye and skin symptoms experienced in the past twelve months. These data were complemented by systematic spirometric tests.

The team concluded that the workers exposed to the milk powder suffer a significant increase in wheezing, breathlessness and various nasal symptoms (blocked or runny nose, itching of the nasal passages and sneezing) compared to the control subjects; wheezing and breathlessness (24% and 33% respectively) were twice those of the control group (12% and 16%). After adjustment for other variables, such as smoking, the relative risk for those two symptoms remained high (1.74 and 2.20). In addition, the exposed workers were apparently twice as likely to have suffered from asthma. It was also found that the workers responsible for adding vitamins complained of eye and skin symptoms twice as frequently as the other employees.

The respiratory function tests recorded a significant reduction in forced expiratory volume over one second among milk powder-exposed workers who complained of respiratory symptoms. The team believe that the symptoms observed are much more typical of a hypersensitivity reaction than a simple irritation. They point to the low levels of particles (mainly milk powder) measured in the air within the factory. Even in the packaging areas, where particle levels were higher, they remained far below the permitted concentration for respirable dust. Milk powder, they explain, contains milk proteins including casein, alpha-lactalbumin and beta-lactoglobulin, compounds with a high molecular weight which typically induce hypersensitivity reactions, although immunoglobulin E antibodies were not measured in the subjects.

The team also believes that respiratory tests could be of benefit to bakers and nannies, who may also suffer occupational exposure to milk powder. A number of cases of occupational asthma have already been recorded in these occupational groups.

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First published August 2008

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