Probiotics are so-called “friendly bacteria”: microorganisms which can be taken in to the body to populate the gut with a healthy symbiotic flora. This gut flora can help suppress the growth of pathogenic bacteria, thus reducing the risk of disease. Probiotics are advocated in the management of a number of conditions including digestive complaints, and there is some evidence to suggest probiotics may actually help prevent the development of allergic conditions such as atopic eczema. However, some individuals may experience an allergic reaction to probiotics.
Florastor is a Probiotic
Most probiotic formulations contain bacterial cultures such as Lactobacillus or Bifidobacterium. However, some fungal organisms can also demonstrate useful probiotic properties, including Saccharomyces boulardii, which is a non-pathogenic yeast. S boulardii is the active ingredient in the probiotic product Florastor. Florastor is a dietary supplement developed from a strain of yeast isolated from lychee fruit by French scientist Henri Boulard in 1923.
Allergic Reaction to Florastor
Very rarely, individuals may experience a severe allergic reaction to the yeast in Florastor. The US Food and Drugs Administration (FDA) advises seeking immediate medical attention if you experience a rash, itching or swelling particularly in the face, tongue or throat, dizziness or difficulty breathing. These symptoms may all indicate an allergic reaction. Individuals should not take Florastor as a probiotic if they have a yeast allergy. In this case, try a probiotic formulation based on a bacterial culture instead. In theory, lactobacillus probiotics may also generate allergic reactions in individuals allergic to dairy products, although no studies have confirmed this. There have been no reports of allergic reactions to Bifidobacterium probiotics.
Like other food allergies, yeast allergy is caused by an inappropriate immune response mediated by histamine. The response is triggered by exposure to certain chemicals or allergens expressed by the yeast. When these allergens are eaten, a type of antibody called IgE is produced which causes the release of histamine in some parts of the body. Possible symptoms caused by the release of histamine include abdominal pain, itching and swelling of the skin, sneezing, a runny nose or a wheeze or cough. Anyone experiencing these types of symptoms after eating bread or drinking alcoholic drinks containing yeast may be allergic to yeast, and is likely to have an allergic reaction to probiotics containing S boulardii.
What to Avoid
Individuals experiencing an allergic reaction after consuming probiotics should see their doctor for advice. If a yeast allergy is confirmed, there are a number of products which should be avoided including certain bread products, wine and beer, stock cubes and vinegar. Fermented or ripe foods such as cheeses, soy sauce and miso may also contain traces of yeast allergens, so these should be tested individually with a four day gap between each testing.
 M Kalliomäki, S Salminen, H Arvilommi “Probiotics in Primary Prevention of Atopic Disease: A Randomised Placebo-Controlled Trial” The Lancet 357:1076-1079 (2001)
 B Kligler, A Cohrssen “Probiotics” American Family Physician 78:1073-1078 (2008)
 “Florastor probiotic” Probiotic-Info.com
 “Florastor Oral Side Effects” RXList Internet Drug Index
 “Florastor® Information Leaflet” US Food and Drug Administration