Editorial Links between allergic rhinitis and asthma still reinforced The nasal airways and their closely associated paranasal sinuses are an integral part of the respiratory tract (1–4). The nasal and bronchial mucosa present similarities, and one of the most important concepts regarding nose–lung interactions is the functional complementarity (2). Most patients with asthma have rhinitis suggesting the concept of Ôone airway one diseaseÕ. However, not all patients with rhinitis present with asthma and there are differences between rhinitis and asthma (5). Epidemiologic studies have consistently shown that asthma and rhinitis often co-exist in the same patients in every region of the world (1, 6–8). The prevalence of asthma in subjects without rhinitis is usually <2%, whereas in patients with rhinitis varies from 10% to 40% (9, 10). Most patients with allergic or nonallergic asthma present rhinitis symptoms (11–14). However, in many instances, symptoms may predominate in one organ and be hidden or unrecognized in other organs even though they exist. Patients with persistent rhinitis appear to have more often asthma but not always (15–18). Adults and children with asthma and documented concomitant allergic rhinitis experience more asthma- related hospitalizations and physician visits, and incur higher asthma drug costs than adults with asthma alone (19–22). These patients also experience more frequent absence from work and decreased productivity. However, some studies have not shown such an association (23). Many patients with allergic rhinitis have an increased bronchial reactivity to methacholine or histamine (24), especially during and some time after the pollen season (25, 26). Patients with perennial rhinitis have a greater bronchial reactivity than those with seasonal rhinitis (24, 27). Nasal and bronchial inflammations are often related (28), and a study in the issue of the Journal (29) shows that vascular endothelial growth factor and interleukin (IL)-5 can be important determinants of the development of bronchial hyperreactivity in allergic rhinitis patients, and that lower levels of other cytokines such as IL-4 and IL-13 may be associated with the absence of asthmatic symp- toms in allergic rhinitis with bronchial hyperreactivity. In the present issue of the Journal, it was found that patients with allergic and nonallergic asthma and chronic obstructive pulmonary disease show increased nasal symptoms and more nasal inflammation (30). These data confirm the Ôunited airwaysÕ concept to be beyond the scope of asthma. The relationships between early life events and subse- quent development of allergy and asthma are often studied in birth cohorts. Many studies have been recently pub- lished in our Journal (31–33). Strachan first proposed the so-called hygiene hypothesis suggesting that infections and unhygienic contact might confer protection against the development of allergy (34). Although this hypothesis has raised enormous amount of data, there are still many questions raised. In this issue of the Journal, using two UK birth cohorts, Bremner et al. (35) investigated infections during infancy in relation to allergic rhinitis, including rarer ones not previously researched in this context, while examining the role of potential confounding variables. Of 30 infectious illnesses investigated, none had strong or consistent associations with allergic rhinitis after adjust- ment for consultation frequency. Except for bronchiolitis, P. Demoly 1,2* , P. J. Bousquet 1,3* 1 DØpartement dÕAllergologie, Chest Clinic, University Hospital, Montpellier, France; 2 INSERM U657, University of Montpellier, Montpellier, France; 3 DØpartement dÕInformation MØdicale, University Hospital, Nimes, France Professeur Pascal Demoly Hôpital Arnaud de Villeneuve 34295 – Montpellier-Cedex 05 France *Members of GA 2 LEN (Global Allergy and Asthma European Network), supported by EU Framework programme for research, contract no. FOOD-CT- 2004-506378. Accepted for publication 3 January 2008 Allergy 2008: 63: 251–254 Ó 2008 The Authors Journal compilation Ó 2008 Blackwell Munksgaard DOI: 10.1111/j.1398-9995.2008.01628.x 251