The term allergy has been misinterpreted, although this condition may affect more than half of the population in some countries. This study aimed to evaluate how health professionals living in the city of Sao Paulo, Brazil, understand the term allergy. Two questions were asked to participants: 1) What is an allergy? and 2) Have you ever developed or seen anyone developing allergies? To what? Data were obtained by interviewing more than 1,000 volunteers. After exclusion criteria were applied, 886 answers were analyzed, 606 from health professionals and 280 from individuals from other fields. The texts were submitted to lexical analysis and word cloud generation. As an additional control, a lexical analysis of a reference text defining the term allergy was used. Results revealed that this method yielded good knowledge of how allergy is understood and that health professionals failed to define the term with accuracy.