Probiotics are defined as live microorganisms which when administered in adequate amounts confer a health benefit (FAO/WHO 2002). The potential benefits include inhibition of pathogens, improved integrity of the gastrointestinal (GI) barrier and enhanced immune responses. These effects may be useful for the prevention and treatment of multiple allergic conditions. Rationale: – Allergies occur more in developed nations. The hygiene hypothesis states that a highly sanitized environment provides insufficient bacterial stimulation at a young age. Without proper ‘training’ the immune system is unable to distinguish harmful bacteria from healthy foods (tolerance). – As we get older, the GI associated immune system continues to play an important role. Unfortunately, the composition of gut microbiota can be altered by diet, stress, aging, antibiotics or infection. – The composition and diversity of intestinal microbiota varies in allergic versus non-allergic children. – Children born via vaginal delivery are less likely to have allergies than those children born via c-section. Exposure to beneficial bacteria in the maternal vaginal tract helps to colonize the child. Also, this benefit may occur in those children who are breast fed. Evidence: – The effectiveness of probiotics for the prevention and treatment of allergies is controversial. There are a large number of published studies with a wide range of results. Several studies show a great benefit and several studies show no benefit at all. – The variable results are likely the result of variable protocols. The strain of bacteria, the amount of bacteria and the age of the patient are important factors in determining outcome. It is likely that different strains produce different immunologic effects leading to different outcomes. One probiotic may help asthma and another may help eczema. Examples of beneficial probiotics include, Lactobacillus rhamnosus HN001 and Bifidobacterium longum BB536. – Eczema (atopic dermatitis). Probiotics have shown value for preventing eczema when given to expecting mothers. Probiotics have shown value for treating eczema when given to young children. – Allergic rhinitis (sneezing). Several studies from Japan have shown decreased allergy symptoms for patients with tree pollen allergy. – Food allergy. Infant formulas supplemented with probiotics may improve the symptoms of milk allergic colitis. Unfortunately, supplementation did not accelerate cow’s milk tolerance in those infants with milk allergy. Conclusion: Probiotics may be a useful adjunct in the fight against allergic disease. They provide a natural way to stimulate the immune system. Most importantly, proper timing may prevent future allergies. Further research is needed to determine which strains are useful and when they should be taken.