As mite allergy is characterized by a continuous allergen exposure, persistent inflammation is always detectable even during symptomless periods. It has been reported that mite allergic patients present a nonspecific hyperreactivity to different stimuli, including hyperosmolar solution. Since it has been reported previously that cetirizine is able to reduce minimal persistent inflammation due to mite allergy, the aim of the study was to investigate the effect of cetirizine on nonspecific conjunctival hyperreactivity. Twenty children with mite allergy were studied; two hyperosmolar conjunctival challenges were performed before and after cetirizine or placebo treatment, lasting one week. Patients treated with cetirizine showed a significant reduction in nonspecific conjunctival hyperreactivity compared to the placebo group (p < 0.05). In conclusion, cetirizine was able to reduce nonspecific hyperreactivity related to allergic inflammation.