Wet washing dried indoors can pose a serious health threat for people with weakened immune systems or severe asthma, doctors have warned.
Research shows clothes draped on drying frames or warm radiators can raise moisture levels in the home by up to 30%, creating ideal breeding conditions for mould spores.
Experts are particularly concerned about Aspergillus fumigatus spores, which can cause lung infections.
Professor David Denning and his team at the National Aspergillosis Centre in Manchester, England have issued the warning after treating a growing number of patients who have inhaled Aspergillus fungal spores.
Prof Denning said: "One load of wet washing contains almost two litres of water, which is released into the room.
"Most of us are either immune to the fungus which grows in these humid conditions, or have a sufficiently healthy system to fight the infection.
"But in asthma sufferers it can produce coughing and wheeziness, and in people with weak or damaged immune systems, such as cancer patients undergoing chemotherapy, Aids patients and people who have an auto immune disease like Craig, the fungus can cause pulmonary aspergillosis - a condition which can cause irreparable, and sometime fatal, damage to the lungs and sinuses.
"My advice would be when in doubt dry wet washing outside, in a tumble dryer or in a well-ventilated indoor space away from bedrooms and living areas to be safe rather than sorry."