Using diaries and interviews, Swedish researchers followed a group of nearly 200 infants, checking in at 18 and 36 months of age. They found that the development of eczema was significantly less likely to occur in babies whose parents had “cleaned” infants’ pacifiers by sucking on them.

Infants in this group were also found to have a different composition of microbes in their saliva, when compared to infants whose parents didn’t use this “cleaning technique”. The authors of the study believe that exposure to parental saliva may accelerate the development of complex oral microbes in the infant, which may help the immune system better tolerate allergens.

Gross? Perhaps. But this research actually falls in line with earlier studies which suggest the human microbiome – a collective term for the trillions of microbes which live on and within our bodies (and actually outnumber our own cells) – plays an integral role in immune system development. These bacteria are on the whole poorly understood, but differences in their composition have been linked with the development of asthma, allergies, diabetes and even cancer.

The research also relates to the ‘hygiene hypothesis’ theory of allergy development. It suggests that, in developed countries, anti-microbial products are overused, resulting in the immune system being underused and failing to mature properly. Allergies develop when the immune system begins targeting normally benign substances (such as peanut or milk protein).

At one point, it was thought that a lack of infections in infants in developed countries was to blame for the rise in allergies, but now some scientists believe it is more likely a disruption of the complex interplay between certain microbes and the developing immune system that is to blame.

Previous studies have linked Cesarian delivery and lack of breastfeeding, which are both factors that impact the diversity and amount of bacteria in infants, to a greater risk of developing allergies later in life.

Does this mean parents should start sucking their kids’ pacifiers? Not so fast, say the study’s authors. This study was quite small, dealt with a specific population, and had no long-term follow-up. Further, larger studies are required before it can be established that this practice will actually help protect infants from developing allergies.

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