The study found that infants who were prescribed antibiotics had a higher risk of developing one or more of these diseases. Antibiotics disrupt the developing microbiome, which causes the immune system to react to harmless foods or pollens, and this can trigger nasal congestion, sneezing, coughing and swelling under the eyes. By the age of five, the risk of developing allergies more than doubled for children who were prescribed antibiotics before their first birthday.

The study involved 1115 children who were followed from birth to age five, 523 of whom had no signs of allergies, and 592 of whom were diagnosed with one or more allergies by age five. The researchers evaluated the microbiome of each child from stool samples collected at three months and one year of age, and found a “bacterial signature” that could be associated with the development of allergies.

The study highlights the importance of avoiding unnecessary antibiotic use in infants, and educating parents about the role of drugs in damaging the microbiome. The study also supported the results of a previous study that breastfeeding for six months also provides protection against allergies because breast milk contains bacteria that promote the development of a healthy microbiome. The researchers hope that their work will contribute to the development of treatment or a method to predict whether a child will develop allergies. Allergies affect one in three children in Canada and millions worldwide.