Various studies in animal and humans have shown a potential beneficial effect of probiotics consumption on allergy. However few studies exist that document their efficacy for upper airways allergies such as allergic rhinitis. The objective of this study is to investigate the effect of short-term oral administration of a L. paracasei or of a blend of 2 probiotics (L. acidophilus + B. lactis) on a nasal provocation test (NPT) with grass pollen, performed out of the pollen season. Adult volunteers with allergic rhinitis are enrolled in a randomized, double-blind study, based on two 4-weeks cross-over periods of product consumption separated by a washout period of 6-8 weeks. Objective and subjective clinical parameters of NPT as well as systemic and nasal immunological markers are compared before and after each treatment.

Inclusion Criteria:

• age 18-40 years old
• history of allergic rhinitis during the latest grass pollen season confirmed by a positive skin prick test to grass pollen (wheal diameter > 3mm) and a positive response to a NPT with grass pollen (combined nasal reaction threshold <= 10000 standardized quality units/ml at the screening phase

Exclusion Criteria:

• any medical condition that could influence the study (pregnancy, viral or bacterial airway infection, active allergic rhinitis)
• uncontrolled asthma (peak expiratory flow <20% of volunteer's best personal value)
• treatment with antihistamine or antibiotic treatment less than two weeks before enrolment or during the trial