The type of allergic sensitization is of central importance in the diagnosis and treatment of respiratory allergic diseases. At least 10% of the general population (and more than 50% of patients consulting for respiratory allergies) are polysensitized. Here, we review the recent literature on (i) the concepts of polysensitization, paucisensitization, co‐sensitization, co‐recognition, cross‐reactivity, cross‐sensitization, and polyallergy, (ii) the prevalence of polysensitization and (iii) the relationships between sensitization status, disease severity and treatment strategies. In molecular terms, clinical polysensitization can be divided into cross‐sensitization (also known as cross‐reactivity, in which the same IgE molecule binds to several allergens with common structural features) and co‐sensitization (the simultaneous presence of different IgEs binding to allergens that may not necessarily have common structural features). There is a strong overall association between sensitization in skin prick tests and total IgE values but there is debate as to whether IgE thresholds are useful guides to the presence or absence of clinical symptoms in individual cases. Molecular information from component‐resolved techniques appears to be of value for diagnosis and treatment decisions. Polysensitization develops over time and is a risk factor for respiratory allergy (being associated with disease severity) and therefore has clinical relevance for treatment decisions. The subterm polysensitization has been defined as polysensitization to between two and four allergens. Polyallergy is defined as clinically confirmed allergy to two or more allergens. Single‐allergen grass pollen allergen immunotherapy (AIT) is safe and effective in polysensitized patients, whereas multi‐allergen AIT requires more supporting evidence. Given that AIT may be more efficacious in moderate‐to‐severe disease than in mild disease, polysensitization could be an indication for this type of treatment. There is a need for flowcharts or decision trees for choosing the allergens for AIT in polysensitized patients and polyallergic patients.

Recent advances in our understanding of T2 inflammation have revealed more diseases in which T2 inflammation is involved. Dupilumab is a recently developed monoclonal antibody that blocks signaling of IL-4 and IL-13, both of which are crucial cytokines in the T2 response. New possible indications are increasingly explored and include skin diseases, such as prurigo nodularis, nummular eczema, allergic contact dermatitis, chronic hand eczema, spontaneous chronic urticaria, bullous pemphigoid, alopecia areata, and Netherton syndrome, as well as respiratory diseases, such as allergic bronchopulmonary aspergillosis, chronic eosinophilic pneumonia, and allergic rhinitis. In addition, eosinophilic gastrointestinal disorders, particularly eosinophilic esophagitis, and food allergy, are also research fields of interest. Here, we review published data and clinical trials examining the use of dupilumab in these disorders.

The prevalence of sensitization to dogs and cats varies by country, exposure time and predisposition to atopy. It is estimated that 26% of European adults coming to the clinic for suspected allergy to inhalant allergens are sensitized to cats and 27% to dogs. This document is intended to be a useful tool for clinicians involved in the management of people with dog or cat allergy. It was prepared from a consensus process based on the RAND/UCLA method. Following a literature review, it proposes various recommendations concerning the diagnosis and treatment of these patients, grounded in evidence and clinical experience. The diagnosis of dog and cat allergy is based on a medical history and physical examination that are consistent with each other and is confirmed with positive results on specific IgE skin tests. Sometimes, especially in polysensitized patients, molecular diagnosis is strongly recommended. Although the most advisable measure would be to avoid the animal, this is often impossible and associated with a major emotional impact. Furthermore, indirect exposure to allergens occurs in environments in which animals are not present. Immunotherapy is emerging as a potential solution to this problem, although further supporting studies are needed.

Managing patients with severe asthma during the coronavirus pandemic COVID-19 is a challenge. Authorities and physicians are still learning how COVID-19 affects people with underlying diseases, and severe asthma is not an exception. Unless relevant data emerges that changes our understanding of the relative safety of medications indicated in patients with asthma during this pandemic, clinicians must follow the recommendations of current evidence-based guidelines, preventing loss of control and exacerbations. Also, with the absence of data that would indicate any potential harm, current advice is to continue the administration of biologic agents during the COVID-19 pandemic in patients with asthma for whom such agents are clearly indicated and have been effective. For the patients with severe asthma infected by SARS-CoV-2, the decision to maintain or postpone biologic therapy until the patient recovers should be a case-by-case based decision supported by a multidisciplinary team. A registry of cases of COVID-19 in patients with severe asthma, including those treated with biologics, will help to address a clinical challenge where we have more questions than answers.

Moderate and severe forms of allergic diseases such as atopic dermatitis and asthma are a challenge for clinicians. In these conditions, which severely affect the quality of life of the patient and frequently have associated allergic comorbidities, the therapeutic options are often very limited. Treatment with systemic corticosteroids and immunosuppressants has adverse effects in the long term, and a significant proportion of patients remain refractory to therapy. In this context, the emerging biological drugs constitute a truly innovative therapeutic approach. A leading example is dupilumab, a monoclonal antibody targeting the α chain of the interleukin (IL)-4 receptor. Dupilumab inhibits the biological effects of the cytokines IL-4 and IL-13, which are key drivers in the TH2 response. The efficacy and safety profile of dupilumab in the treatment of allergic diseases has been tested for more than 10 years in a variety of large clinical trials in atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyposis, and eosinophilic esophagitis. In 2017, the United States Food and Drug Administration and the European Medicines Agency approved the use of dupilumab for the treatment of adult patients with moderateto-severe atopic dermatitis whose disease is not adequately controlled with prescribed topical treatment. The results of phase III clinical studies of dupilumab in patients with persistent, uncontrolled asthma have been highly promising. The safety and tolerability profile of dupilumab has proven to be very favorable in long-term clinical trials. In this review, we focus on the mechanism of action of dupilumab, its development, and its impact on daily clinical practice in allergic diseases.