Fungus expert Joan Bennett did not believe in so-called toxic mould - the cause of "sick building syndrome" and many lawsuits - until her New Orleans home was flooded during Hurricane Katrina in 2005.
When she got a whiff of the foul air that the black goo had created in her home, she decided to change her research focus and try to find out how and if the fungi that took over most of the flooded homes on the Gulf Coast might make people ill.
"The overwhelming obnoxiousness of the odour and of the enveloping air made me start to believe in something that I had never believed in before - sick building syndrome," Dr Bennett, of Rutgers University in New Jersey, told a news conference.
But it has been more difficult than she thought.
She believes that moulds could potentially cause illness in certain susceptible people via volatile organic compounds - gassy versions of chemicals produced as the organisms metabolise food. She has been unable to show this in the lab so far, but, she told a joint meeting of the American Society for Microbiology and the Infectious Diseases Society of America.
She has tested various moulds on the laboratory roundworm C. elegans. "Sometimes the worm swims away and sometimes the worm does nothing and sometimes the worm eats the fungus," Dr Bennett said.
"I am actually looking for something that has never been discovered by methods that have never been worked out."
Yet hundreds of lawsuits have been filed - and some won - by people claiming mould in their homes or workplaces has made them ill.
David Denning of the University of Manchester in Britain said it is plausible that moulds and fungi would emit volatile organic compounds.
If these can be found, they could form the basis of diagnosing fungal illness as well - perhaps using a breath test. People with fungal infections of the lungs, such as aspergillosis, would release these chemicals when they breathed.
"A certain group of severe asthmatics - about a million people - are sensitive to a number of different fungi," Dr Denning told the news conference. These include Aspergillis and Candida.
"This is almost certainly a genetic issue," he added. "If you have a predisposition (to asthma), you probably have an additional predisposition to fungal sensitisation."
David Goldman, a paediatrician in the Bronx, New York, said asthma rates in his borough are disproportionately high, and he blames in part Cryptococcus neoformins, a microbe found in pigeon droppings that causes disease in immune-compromised people.
"We believe this fungus contributes to asthma by modulating the immune response," Dr Goldman told the news conference.
Both Dr Goldman and Dr Denning said treating patients with antifungal drugs such as itraconozole and fluconazole helped relieve the symptoms of patients with severe asthma.