A common mould that causes an allergic reaction in asthmatics actually grows in many sufferers' lungs, scientists have said.
The discovery was made during research into the impact on asthmatics of a common environmental mould, Aspergillus fumigates, usually found in soil and compost heaps.
The research, led University of Leicester scientists at Glenfield Hospital in Leicester, has been published in the December issue of the American Journal of Respiratory and Critical Care Medicine.
Professor Andy Wardlaw, from the University of Leicester, said: "Asthma is a very common condition where the breathing tubes (bronchi) can go into spasm making it difficult to breathe.
"Around a fifth of adults with severe asthma, which they have had for a long time, get permanent (fixed) narrowing of their bronchi. "It is known that A. fumigatus can grow in the lungs of some people with asthma and mould allergy, which can cause severe lung damage.
"This problem is thought to only affect a very small number of people with asthma.
"However, about half of people with severe asthma have evidence of allergy to moulds like A. fumigatus."
Researchers in the Institute for Lung Health at the university and Glenfield Hospital carried out a study funded by the Midlands Asthma and Allergy Research Association (MAARA) and the European Regional Development Fund (ERDF).
They looked at whether the problem of A. fumigatus growing in the lungs is more common than previously thought, and whether this could explain the fixed narrowing of the airways in some people with asthma.