Adding probiotic bacteria to your daily drink may be able to modify the response of the immune system to allergens like grass pollen, a new study by scientists at the Institute of Food Research has said.

The researchers say that they have noted such beneficial changes in a human study.

They, however, have also made it clear that they are not recommending people with hay fever to rush to the supermarket shelves, as the changes they observed might not have an immediate effect on symptoms.

"This was a pilot study based on small numbers of patients, but we were fascinated to discover a response. The probiotic significantly reduced the production of molecules associated with allergy," says research leader Professor Claudio Nicoletti.

When a person contracts hay fever, his/her immune system mistakes the infection-causing fungal or pollen spores for harmful invaders, and produces excessive amounts of the antibody IgE to bind to them and fight them off.

The researchers say that IgE stimulates the release of histamine to flush out the spores, and this irritates the airways making them swell and producing the symptoms of hay fever.

During the course of study, volunteers with a history of seasonal hay fever were administered milk with or without live bacteria daily for over five months.

Given the double-blinded and placebo controlled nature of the study, neither the volunteers not the scientists knew who had been assigned the probiotic drinks containing Lactobacillus casei, a bacterial species that has been widely studied for its health promoting properties.