**1. Introduction**

Episodes of breathlessness or wheezing are common in preschool children primarily in the first 2 years, being estimated that 50% of infants have episodes of this nature, and their causes are needed to be known. The insufficient development of the immune system opens up to fre‐ quent viral infections, but other factors can contribute, such as the home environment, partic‐ ularly if the mother is a smoker. Given the importance of genetic predisposition, family history of allergic diseases and asthma in particular is always is to be known, taking into account the famous expression 'all that wheezes is not asthma'.
