The placebo will have the same form, colour, taste and aspect. The allowed concomitant treatments are the already established treatments for associated pathologies not liable to have an impact on the proper conduct of the study and the rescue medications allowed in the first-line adjuvant treatment (oral or topical antihistamines [nasal or eye] and eye cromoglycate, topical nasal corticosteroids [in case of failure or insufficiency of those above]).