Yeast and mould allergies

What is involved in yeast and mould allergies and how does one manage them? Dr Janice Joneja offers some insight.

Moulds and yeasts are tiny single-celled fungi, much smaller, but of the same biological group as mushrooms. Fungi depend on nutrients that they get from their hosts. These hosts can be dead or decaying plant or animal matter on which they live (saprophytes), or living plant or animal matter (parasites). They can also live in a symbiotic relationship with another organism to which they do no harm (symbionts). They thrive in nearly all environmental conditions. Out of over 100,000 known fungal species, about 100 are known to cause infections in humans and animals.

Many of these species have been implicated in inhalant allergy, most commonly asthma. About 150 individual fungal allergens from approximately 80 mould genera have been identified in the last 20 years. (1) Other allergies triggered by moulds include hay fever, eczema, hives, and very rarely, anaphylaxis. (2) However, in hay fever, eczema and hives the role of fungi as the the primary cause of the condition has yet to be definitively established. (3)

A person sensitised to fungi and fungal spores produces IgE antibodies against the fungal allergenic proteins; these can be detected in blood tests. Skin tests for the fungal allergens are also usually positive. This suggests that IgE is present in the body and could trigger inflammatory/allergic response whenever it encounters the allergen. The allergen is usually inhaled but could also be found in foods containing the specific allergen to which the patient is sensitised.

Those who are sensitive to inhaled fungi and fungal spores need to avoid inhaling all sources of the fungi – such as in the moist soil of houseplants, damp rooms and especially basements where moulds grow. Because mould spores are released from damp ground softened by the first thaw of spring, mould-sensitive people with asthma should limit their time outdoors to avoid inhaling the spores in the air at this time of year.

A small percentage of asthmatic people who are sensitive to inhaled fungal spores, and some non-asthmatic people, develop eczema or urticaria (hives) when they come into contact with their specific allergen or if they eat or drink foods which contain yeast or moulds. Extremely sensitive people can even suffer an anaphylactic reaction, with breathing difficulty, hives, swelling in the air passages and the throat and cardiac symptoms.(4) These people must be particularly careful to avoid all sources of fungi in their diet.

Allergy to yeast is often associated with inhalant allergy to Saccharomyces cerevisiae in conditions such as baker’s asthma (5) and some cases of eczema. (6) The yeast Pityrosporum ovale is sometimes associated with eczema, and studies suggest that allergen-specific IgE to the yeast is present in sensitised people with eczema. (7)

Yeast and Mould in Foods

Mould colonies are often seen growing on the surface of moist foods such as bread, jam, and cheese. Moulds range from a unicellular to a filamentous form on these media.

Some mould-restricted diets suggest avoiding wheat flour because in the past, stored wheat was often contaminated by mould. However, because modern flour milling does not permit the use of mouldy wheat, flour need not be avoided.

Fresh fruit may also be a source of mould. Fresh fruits are prone to fungal contamination in the field, during harvest, transport and marketing, and in the home. (8)

Moulds are used in the production of certain types of cheese, such as the soft white cheeses Brie and Camembert (which are inoculated with Penicillium camemberti), blue cheeses (which are inoculated with Penicillium roqueforti or Penicillium glaucum), and goat milk cheeses (which may be treated with white or blue molds).

Some lists of foods to avoid in mould sensitivity include milk, because it could be a source of penicillin, an antibiotic derived from the mould belonging to the genus Penicillium. In the past, dairy cows were treated with penicillin to protect them from infection. However, this practice has been discontinued because of the danger to penicillin-sensitive people, so milk does not need to be avoided.

Yeasts (Saccharomyces species) are used in food production to ferment the nutrient source on which they grow. In baking, fermentation of the substrate (starch) leads to the generation of gases (mainly carbon dioxide), which is the process that makes the dough rise in breads and other leavened baked products. Another by-product of yeast fermentation of a substrate (sugar) is alcohol. This is the basis of production of alcoholic drinks. Both baker’s and brewer’s yeast are strains of Saccharomyces cerevisiae.

Savoury spreads made from yeast extract, a by-product of beer brewing, are popular in many parts of the world. In Britain, the product is marketed as Marmite; in Australia as Vegemite; and in Switzerland, there is a similar product called Cenovis. Meat extract products and some gravy brownings usually contain yeast extract. The label will indicate if yeast is present in the product. All these products contain Saccharomyces cerevisiae.

Saccharomyces exiguus (also known as S. minor) is a wild yeast found on plants, fruits, and grains that is occasionally used for baking; however, it is not generally used in a pure form but comes from being propagated in a sourdough starter in which lactobacilli are also included.

Yeast is a source of B vitamins and is present in many multivitamin preparations containing B vitamins. The B vitamins thiamin, riboflavin, folic acid, and niacin are usually derived from the yeast Saccharomyces cerevisiae.

Milk and milk products may also contain yeasts. A 1987 study reported that yeasts were isolated, identified, and enumerated from 161 samples of retail dairy products. Highest yeast populations (up to 106 to 107 cells/g) were found in yogurt and cheese, while lower counts occurred in pasteurised milk, cream, butter, and ice cream. (9) While not all of these products are restricted on a yeast and mould-free diet, it is wise to keep in mind these possible sources of yeast if symptoms do not resolve on a restricted diet. If symptoms do resolve when these foods are restricted, that would suggest a sensitivity to this source of yeast.   
Dietary Management
Dietary management of yeast and/or mould sensitivity requires the elimination of all foods that might contain yeast or mould. Foods which should be excluded include:
• baked products leavened with yeast
• many cheeses
• certain fruits and vegetables
• certain beverages
• all mouldy foods
• vitamin-enriched flours because enriched flours contain vitamins that may be derived from yeast

Even if a cheese does not have mould in its production (eg, Cheddar), cheese and other milk products provide a rich substrate that is ideal for mould growth. Therefore, cheese, even when stored in the fridge, should be carefully examined for the presence of a mould on its surface and avoided. It is not sufficient to cut out the mouldy bits, as mould filaments can invade the cheese below the surface and products of mould growth can be present even when the mould itself seems to have been cut out.

Foods containing sugar are particularly vulnerable to colonisation by moulds so jams, jellies, and other sugar-based products should be avoided if mould is visible on their surface. Some moulds will grow even on frozen food. Examine any food that has been stored for a prolonged period of time for the presence of mould and throw it away if any mould is visible.

Leftover foods and leftover tea and coffee are also potential media for the growth of moulds so only eat or drink fresh foods and freshly brewed tea and coffee. All raw fruits and vegetables should be carefully examined for the mould and should not be eaten if any mould is found. It is not enough to just wash the food.


Candida albicans is a dimorphic fungus, which means that it grows as a yeast form in a carbohydrate medium and forms hyphae (strands) when the medium is low in nutrients. Thus, it is commonly referred to as a pseudoyeast.

Candida species are common in the body’s resident microflora. Usually they are innocuous, as they are kept in check by other resident microorganisms such as bacteria. However, this balance can be upset when, for example, antibiotics eliminate several species of bacteria or the immune system is not functioning efficiently. In these instances, Candida multiply unchecked and soon cause infections such as oral thrush, vaginal moniliasis, and skin eruptions.

The role of Candida as a cause of allergy has been much disputed. Positive skin reactions often occur in people without clinical evidence of Candida infection or allergic disease. Some practitioners believe that repeated imbalances in Candida in the body can lead to chronic Candida sensitivity, which in turn can lead to numerous food and chemical sensitivities. (10) A “Candida diet” is prescribed to treat this condition, usually excluding foods that contain sugars and more complex carbohydrates. In addition, the Candida-sensitive individual is advised to avoid dietary forms of other fungi, which are believed to cross-react with Candida and produce similar reactions.

Although Candida infection or sensitivity may contribute to mould and yeast sensitivity, this connection has not been proven. (11) This article refers only to a yeast and mould allergy (usually IgE-mediated hypersensitivity) and the advice given should not be used to manage a suspected Candida sensitivity.


  1. Simon-Nobbe B, Denk U, Pöll V, Rid R, Breitenbach M. The spectrum of fungal allergy. Int Arch Allergy Immunol. 2008;145:58-86.
  2. Bennett AT, Collins KA. An unusual case of anaphylaxis: mold in pancake mix. Am J Forensic Med Pathol. 2001;22(3):292-295.
  3. Bush RK, Portnoy JM, Saxon A, Terr AI, Wood RA. Position paper: the medical effects of mold exposure. Envir Occup Respir Disorders. 2006;117(2):326-333.
  4. Airola K, Petman L, Mäkinen-Kiljunen S. Clustered sensitivity to fungi: anaphylactic reactions caused by ingestive allergy to yeasts. Ann Allergy Asthma Immunol. 2006;97(3):294-297.
  5. Baldo BA, Baker RS. Inhalant allergies to fungi: reactions to bakers’ yeast (Saccharomyces cerevisiae) and identification of bakers’ yeast enolase as an important allergen. Int Arch Allergy Immunol. 1988;86:201-208.
  6. Kortekangas-Savolafnen O, Kalimo K, Lammintausta K, Savolainen J. IgE-binding components of baker’s yeast (Saccharomyces cerevisiae) recognized by immunoblotting analysis. Simultaneous IgE binding to mannan and 46–48 Kd allergens of Saccharomyces cerevisiae and Candida albicans. Clin Exp Allergy. 1992;23(3):179-184.
  7. Wessels MW, Dolkes G, Van Ieperen-Van Dijk A, Gkoers Wj, Young E. IgE antibodies to Pityrosporum ovale in atopic dermatitis. Br J Dermatol. 1992;125(3):227-232.
  8. Tournas VH, Katsoudas E. Mould and yeast flora in fresh berries, grapes and citrus fruits. Int J Food Microbiol. 2005;105(1):11-17.
  9. Fleet GH, Mian MA. The occurrence and growth of yeasts in dairy products. Int J Food Microbiol. 1987;4(2):145-155.
  10. Crook WG. The Yeast Connection: A Medical Breakthrough. Jackson, TN: Professional Books; 1984.
  11. Position statement: Executive Committee of the American Academy of Allergy and Immunology. Candidiasis sensitivity syndrome. J Allergy Clin Immunol. 1986;78(2):271-273.

Additional Resources
For client education material on yeast and mold allergy and other food allergies and intolerances, look for Food Allergies and Intolerances: Client Education Tools for Dietary Action / Tools for Dietary Management

First published April 2014

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