Various studies in animals 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 Lactobacillus paracasei on a nasal provocation test (NPT) with grass pollen, performed out of pollen season. Adult volunteers with allergic rhinitis are enrolled in a randomized, double-blind, placebo-controlled study, based on two 4-weeks cross-over periods of product consumption (probiotic-fermented milk versus placebo), separated by a washout period of 6-8 weeks. Objective and subjective clinical parameters of NPT as well as systemic and nasal immunological parameters are compared between the two treatment periods.

Inclusion Criteria:

• age 18 to 35 years
• history of allergic rhinitis to grass pollen confirmed by either a positive skin prick test (wheal diameter >3 mm) or specific IgE for grass pollen (>0.35 kU/L) as titrated by UniCAP 100 (Pharmacia Diagnostics, Uppsala, Sweden) and no history of perennial rhinitis
• a nasal reaction threshold of 10'000 standardized quality units (SQs)/ml grass pollen or less 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