Bad ventilation

Ill-ventilated rooms
Inadequate ventilation
Lack of ventilation
Double-glazed homes with high humidity and fitted carpets are most likely to exacerbate asthma, particularly if dust and pets are also present. Children in west German cities have high levels of antibodies against house-dust mites and cat fur -- the most common household triggers of asthma -- and at levels three to five times higher than their contemporaries in east Germany (no other differences were found in other antibodies, such as those to grass pollens). The incidence of a related disorder, nasal allergy or hay fever, was 23% in Hamburg against around 13% in Erfurt.
Reduced by 
(E) Emanations of other problems