Products with so-called 'friendly bacteria' are widely available

The six-year research at Swansea University's School of Medicine aims to see if the foods, such as live yoghurt, can boost infants' immune systems.

The �600,000 project, funded by the development arm of the Welsh assembly, will involve firms in the UK and US.

Wales has 30% more asthma-caused hospital cases than the rest of the UK.

Studies show asthma rates in UK children have quadrupled since the 1970s. In Wales, the condition kills around 80 people annually and affects more than 250,000.

Along with eczema and hay fever, it is one of the allergic diseases which experts increasingly link to the cleanliness of homes.

The Swansea research is the first in the UK to repeat an experiment in Finland five years ago which suggested that probiotic organisms, or friendly bacteria, can help to prevent allergic diseases.

Paediatrician Professor Gareth Morgan has begun recruiting 600 pregnant women at the adjacent Singleton Hospital, half of whom will be given a food supplement powder to give to their child from 36 weeks.

The study will increase the bacteria in the infants' bowels

He said: "One of reasons (for allergic diseases) is that we're much cleaner and much more hygienic, so children are no longer exposed (to bacteria in the environment) as they used to be.

"So they don't develop the resistance they are designed to develop.

"By putting these germs, these friendly bacteria, back in the environment, we are pushing the babies' immune systems to its natural state, to the state it has evolved to be in."

'Beneficial effects'

He added there was already some scientific evidence that giving probiotics to babies prevents eczema, but more evidence is needed on whether they prevent hay fever and asthma.

The study is constructed so that neither the medics nor the families know if a child is receiving the friendly bacteria or a neutral control substance.

A first report on any apparent beneficial effect is due in June 2006 with follow-ups over a further five years.

The Welsh Development Agency (WDA) is funding the project through the Knowledge Exploitation Fund, an initiative aimed at ensuring ideas from universities in Wales are put into practice and encourage local industry.