Giving babies friendly gut bacteria can protect them from developing eczema in childhood, researchers suggest.
The children were given the bacteria as babies
Previous research has suggested that giving pregnant women and newborns bacteria halves the incidence of eczema at the age of two.
This latest study, from Finland, indicates that children still benefit from the effects of the bacteria at the age of four.
UK researchers welcomed the findings, but said parents should not start feeding probiotics to their babies until further studies had confirmed their benefits.
The Finnish research team were looking at the incidence of atopic eczema, thought to be a hereditary condition in which people are sensitive to allergens in the environment which are harmless to others.
When you're dealing with young babies' health and feeding them bacteria, you need to be sure that they are safe and effective
Professor Ashley Woodcock, Wythenshawe Hospital
The incidence of atopic disease is growing in developed countries.
Some experts suggest this is down to a lower level of exposure to bacteria among young children, which affects the full development of their immune systems - the so-called "hygiene hypothesis".
This latest study looked at a group of 107 children, half of whom had been exposed to a particular strain of the gut bacteria Lactobacillus as babies.
Their mothers took Lactobacillus GG in the last few weeks of pregnancy, and for the first six months of their babies' lives.
The rest were given dummy pills.
All came from families with a history of eczema.
It was found that children who had been exposed to the bacteria were 40% less likely to develop the condition by the age of four than the other group.
However, probiotics appeared to have no protective effect against asthma or rhinitis.
Dr Marko Kalliomaki from the Turku University Central Hospital in Finland told BBC News Online the researchers would continue to follow the children to see if the protective effect continued.
He added: "At the moment, we're not issuing any recommendations about giving children probiotics to mothers as there have to be more studies which support our hypothesis before such advice can be given."
Professor Ashley Woodcock, of the North West Lung Centre at Wythenshawe Hospital, Manchester, told BBC News Online the results could not be extrapolated to all children.
He said it appeared all the children had been breastfed, a factor known to reduce the risk of children developing eczema, so the results could not be applied to bottle-fed children.
Professor Woodcock, who is carrying out his own study into the effects of probiotics on eczema risk in three- to six-month-old babies, said: "This is a different breed of the lactobacillus. It's one that is used in Finland and is not one of the common UK brands.
"It is a different breed, and they all have different effects."
He warned parents not to start giving babies probiotics without further evidence of their benefits, and said giving babies the wrong bacteria could affect the development of their immune system.
The research is published in The Lancet.