In this randomized, double-blind, placebo-controlled study, participants with seasonal allergies will receive a daily probiotic or placebo for 8 weeks. Questionnaires will assess health-related quality of life, stress, physical activity, gastrointestinal symptoms, adverse events, and compliance. In a subset of subjects, stool and blood samples will be collected at baseline and at week 6 of the intervention (estimated to be peak allergy season) to characterize microbial communities and immune function.