Phase IV, human pharmacology, exploratory, randomized, 3-way (3 treatment periods) cross-over, double blind, double dummy, placebo controlled study to compare levocetirizine and cetirizine by means of IR thermography.

Inclusion Criteria:

• Healthy male Caucasian subject aged between 18 and 55 years (both inclusive).
• Subject must have a positive prick test to histamine (wheal diameter ≥ 6 mm with histamine dihydrochloride (100 mg/mL) and ≤ 3 mm with diluent control).

Exclusion Criteria:

• History of allergic disease, documented or suspected, including but not limited to: asthma, whether or not considered as allergic; nocturnal cough episode suspected to be of asthma-equivalent nature (three or more consecutive nights resulting in sleep disturbances) ; allergic rhinitis, conjunctivitis or sinusitis; nasal polyposis; dermatitis of the face or neck; drug or food allergy.
• Any clinically significant vascular disease such as hyper- or hypotension, venous disorder, vasculitis etc.
• History of hot flushes and any other vasomotor disorders.
• ENT infection or Upper Respiratory Tract Infection not completely cured at least one week before inclusion.
• Any known history of laryngeal edema.
• Nasal structural abnormalities (e.g. deviation of the nasal septum…).
• Recent immunotherapy
• Skin irritants or UV exposure 48 hours before each visit.