Asthma rates have increased dramatically since the 1950s and now affect up to 20 per cent of children in western countries. The researchers analyzed fecal samples from 319 children involved in the CHILD Study.

Analysis of the gut bacteria from the samples revealed lower levels of four specific gut bacteria in three-month-old infants who were at an increased risk for asthma.

Most babies naturally acquire these four bacteria, nicknamed FLVR (Faecalibacterium, Lachnospira, Veillonella, Rothia), from their environments, but some do not, either because of the circumstances of their birth or other factors.

The researchers also found fewer differences in FLVR levels among one-year-old children, meaning the first three months are a critical time period for a baby's developing immune system.

The researchers confirmed these findings in mice and also discovered that newborn mice inoculated with the FLVR bacteria developed less severe asthma.