Sentence:  Whatever factor is invoked to explain the increase in asthma must also be capable of explaining other outbreaks of <WSD>atopy</WSD>. 
Meaning of the word marked with <WSD> tags:  A hereditary disorder marked by the tendency to develop localized immediate hypersensitivity reactions to allergens such as pollen, food etc and is manifested by hay fever, asthma, or similar allergic conditions; generally considered to be caused by the interaction of environmental and genetic factors.