Allergen immunotherapy (AIT) has a clear evidence of efficacy and safety, as shown by a number of meta-analyses. However, a number of issues limit the use of AIT, many of them being not actually supported by solid data from the literature. In particular, several contraindications to AIT deserve to be argued, being needed to accurately balance in single cases the benefits versus the disadvantages. This concerns comorbidities, such as autoimmune diseases and malignancies, concomitant drug treatments, particularly β-blockers and angiotensin-converting enzyme inhibitors, pregnancy, patient's age, the severity of asthma, allergen polysensitization and the period of starting the treatment. Another important aspect producing misconceptions on AIT is the quality of the allergen extracts, because currently a patient with respiratory allergy to a given source may be prescribed to treat his allergyby products with very different quality. Improving characterization and standardization of allergen extracts will pave the way to the general acknowledgment of AIT as an effective treatment.