More than 600 babies and their mothers will take part in a Swansea University study to see if friendly bacteria can prevent children developing allergies.
Baby Jacob is among the first to take part in the study
Mothers are giving their new arrivals natural food supplements to establish if they boost their immune system.
Gill Heinrich, who gave birth to baby Jacob last week, is the among first to join the seven-year study.
Jacob's father suffers with hay fever and the hope is research will help prevent such conditions in the future.
The £600,000 study is joint a project between Swansea University's School of Medicine and Baglan-based Cultech Ltd.
Dr Steve Allen of the School of Medicine said there was already some scientific evidence that giving probiotics, naturally occurring supplements that contain friendly bacteria, to babies prevents allergies such as eczema.
Over the coming months more than 600 volunteer mothers who attend ante-natal care in Swansea will be recruited for the trial.
Half the recruits will take probiotics during the last month of pregnancy and then give it to their babies during the first six months of their lives.
The other half will take placebo, a dummy alternative, as a control.
"We will recruit mothers over about 18 months or so and follow the children for five years," he explained.
Mothers will not know if they are receiving the placebo or probiotic supplements.
After five years the children will be assessed to see if those taking the probiotic have less allergic disorders than the other group.
Dr Allen said allergic disorders such as eczema, hay fever and asthma were very common in south Wales, with as many as one in three suffering from asthma.
Mrs Heinrich, 37, from Sketty, said she had always been interested probiotics as her husband suffered hay fever.
"The supplement is just a pinch of powder and even though I am breast feeding I find it no trouble at all to give to Jacob," she said.
"Of course we will only find out later if he was on the probiotic or placebo and what impact they might have had on his immune system."