A baby’s first poo reveals if they are at risk of allergies and asthma

Children could be set on a path to developing allergies, asthma and eczema before they are born.

Analysis of a baby’s first stool, known as meconium, shows that a lack of certain biochemicals and gut bacteria normally seen in the faeces is linked with a higher risk of allergies and other conditions.

Allergic conditions such as food allergies, hay fever, asthma and eczema are caused by the immune system overreacting to harmless compounds in the environment. Many studies have found links between such immune system reactivity and a lower diversity of gut bacteria, or microbiome. One idea is that a diverse ecosystem of beneficial bacteria helps to “train” the developing immune system to tolerate non-harmful compounds.

The new research, by Charisse Petersen at the University of British Columbia in Vancouver and her colleagues, analysed the meconium of 100 babies who had been part of a larger, ongoing Canadian study of child development. Meconium isn’t normal faeces, but a mixture of substances that entered the baby’s mouth in late pregnancy, such as amniotic fluid, skin cells and substances made by the baby’s skin.

Chemically, it includes a range of fatty molecules, amino acids and other compounds from the mother’s diet. “Meconium is kind of a time capsule because it contains all of the molecules that the baby was exposed to,” says Petersen.

Most allergic conditions develop in later childhood, so to get results when the infants were 1 year old, the team did a skin test that measures the reactivity of the immune system.

The quarter of the group with the most chemically diverse meconium had half the risk of an overreactive immune system, compared with the quarter who had the least variable meconium. There was a similar-sized link between diverse gut bacteria in the meconium and later immune reactivity.

“What’s in the meconium becomes the food source for all of those bacteria that we want to colonise us,” says Petersen. “The more diverse the food source, the more likely you’re going to be able to support the colonisation of all of those beneficial microbes.”

Parents could try to lower their children’s risk of allergic conditions through steps such as avoiding unnecessary antibiotics and trying to get their children playing outside more, says Petersen. Another factor linked with a lower risk of allergies is having a pet dog in the house, says Tom Marrs at King’s College London.