Women infected with a common stomach bug have a lower risk of developing multiple sclerosis (MS), a West Australian research team has found.

Helicobacter pylori (H. pylori) bacteria infects about 50 per cent of the world's population.

While it remains symptomless in most people, it was discovered to be the cause of stomach ulcers by Australian Nobel Prize laureates Professor Barry J. Marshall and Professor Robin Warren.

A new study of about 850 people found that women infected with the bacteria were less likely to have MS than women not infected.

This was not the case for men, who are three times less likely to develop the autoimmune disease compared to women.

The study's authors think infections like H. pylori could move the balance of the immune system to a less inflammatory state, and as a result the risk of immune sensitivity is reduced, as are the chances of developing autoimmune disorders like MS.

Previous studies have investigated the possibility of a link between H. pylori and MS, but used relatively small numbers of people and produced inconsistent results.

The WA study was the largest of its kind and used blood and clinical information from a database of the state's registered MS sufferers, which was created 18 years ago.

Research leader clinical Professor Allan Kermode, from the WA Neuroscience Research Institute, said the results were encouraging.

"The results from this research may indicate that H. pylori has a protective effect against MS and also bolsters evidence for the role of the hygiene hypothesis in autoimmune diseases," he said.

The hygiene hypothesis suggests that early life exposure to infections may aid the human immune system by priming it, making the development of allergies and autoimmune conditions later in life less likely.

Researchers hope the discovery could pave the way for creating drugs that imitate the effect of the bacteria and prevent MS from developing.

The MS Society of WA has praised the efforts of the West Australian team.

"It is encouraging to see that Australian researchers are at the forefront of research discoveries and actively collaborate to ensure that progress can be made faster," chief executive Marcus Stafford said.

"This research gives hope to the people living with MS and their families."

The research was published this week in the Journal of Neurology, Neurosurgery and Psychiatry.