Lactobacillus paracasei is a probiotic strain that has been investigated for its potential to alleviate symptoms of allergic rhinitis—a condition characterized by inflammation of the nasal passages due to allergens such as pollen or dust mites. Scientific interest in this strain for allergic rhinitis stems from the hypothesis that certain probiotics may modulate the immune system, shifting it away from the Th2-dominated responses that underlie allergy symptoms.

Several randomized controlled trials (RCTs) and meta-analyses have examined the efficacy of L. paracasei in managing allergic rhinitis. Notably, clinical studies have shown that supplementation with specific L. paracasei strains (such as L. paracasei LP-33 and L. paracasei ST11) can reduce nasal congestion, sneezing, and other allergy symptoms compared to placebo. For example, a 2009 double-blind RCT published in the journal Clinical & Experimental Allergy found that L. paracasei LP-33 supplementation reduced symptom severity in subjects with perennial allergic rhinitis. The proposed mechanisms involve modulation of cytokine production and enhancement of the intestinal barrier, which may contribute to decreased systemic allergic responses.

However, while the evidence is promising and suggests a beneficial effect, it is not yet robust or universal enough to reach the highest level of clinical recommendation. Results can vary depending on the strain used, duration of supplementation, and patient characteristics. Therefore, the evidence is rated as moderate (3/5), indicating scientific validation but with some limitations and a need for further large-scale, high-quality studies.