Yeast is a type of fungus. Certain foods and drinks, such as baked goods and alcoholic beverages, may contain or use yeast. People who are allergic to yeast should try to avoid products containing yeast.

Published in 1983, The Yeast Connection attributed a wide range of symptoms to a condition termed yeast hypersensitivity — or allergy. Moreover, the authors suggested that many were allergic, or at least sensitive, to yeast.

In 1986, the American Academy of Allergy and Immunology issued a statement calling into question the existence of yeast hypersensitivity. It highlighted scientific shortcomings of research that linked yeast to health problems. In spite of these doubts, some researchers continue to publish on the topic.

Fast facts on yeast allergies:

  • Yeast hypersensitivity remains controversial.
  • Yeast hypersensitivity syndrome may not involve an allergy. It is important to distinguish the purported effects of this syndrome from a real allergy to yeast.
  • People with severe yeast allergies may need to avoid eating outside the home.
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Yeast is a fungus that is present in many foods.

Allergy to inhalation of fungal spores is a well described trigger for allergic rhinitis (sneezing, stuffy nose, itchy eyes). Allergic symptoms due to direct ingestion of yeast or other fungi remain very poorly understood.

There are little to no rigorous studies on yeast allergy to clarify the typical presenting symptoms, treatments, diagnoses, foods to avoid, or risk factors. Knowledge of yeast allergy comes only from case reports and case series, which suggests that true allergy to ingestion of yeast is exceedingly rare.

Fungi, including mold and yeast, reproduce through tiny spores that may travel through the air. People with allergies to these substances may develop respiratory symptoms when they inhale the spores.

Symptoms of an allergy to inhaled yeast and mold spores may include:

  • sneezing
  • cough
  • itchy eyes
  • congestion
  • breathing difficulties

This allergy may also trigger an attack in people with asthma.

However, the American College of Allergy, Asthma, and Immunology caution that no study has conclusively linked airborne allergens to severe allergic reactions. Even among people who have a severe allergy to yeast in food, inhaled yeast is unlikely to trigger a reaction.

Some alternative medicine practitioners who believe in yeast hypersensitivity promote the use of antifungal medications, such as nystatin. There is little scientific evidence supporting the use of these drugs in people who do not have fungal infections.

The most effective treatment for a diagnosed yeast allergy is to avoid foods containing yeast. People who eat yeast and develop mild allergic reactions, such as rashes, can often manage their symptoms with antihistamines.

Those with anaphylactic reactions will need emergency medical care if they accidentally eat yeast. An epinephrine injector can prevent anaphylaxis from turning deadly.

Practitioners of alternative medicine often diagnose yeast hypersensitivity syndrome, based on symptoms alone.

True yeast allergies can be diagnosed by an allergist, who will ask about a history of allergic reactions to certain foods. They may also perform a skin prick test to confirm the diagnosis. This will involve the allergist applying a tiny amount of yeast to the skin, to test for a reaction.

They may also recommend a blood test, which will determine the presence of an antibody protein that can indicate a food allergy.

People with a history of anaphylactic reactions to yeast or any other allergen in food may need to undergo comprehensive testing. This can identify additional allergens and may prevent life-threatening reactions.

Read labels carefully to reduce the risk of accidentally consuming yeast. Foods that contain yeast include:

  • Baked goods: Yeast is commonly used to leaven foods, such as cakes and sourdough breads.
  • Alcoholic beverages: Yeast is used to ferment sugar in most alcoholic beverages. However, distilled spirits may not contain very much yeast.
  • Some food spreads: Products such as Marmite and Vegemite contain yeast.

Because some people with yeast allergies may also be allergic to mold, testing can help to determine whether additional foods may cause reactions. These can include cheeses made with mold.

An allergy occurs when the body overreacts to a substance that may be harmless to other people. The body treats this substance — the allergen — like a dangerous invader, and a range of symptoms can develop.

Researchers have yet to agree about why certain people develop allergies, but a combination of environmental factors and genetics may be to blame.

There has been little research into risk factors for yeast allergies. It is impossible to predict with certainty whether someone will develop this allergy and how severe their reactions will be. If a person suspects that they have a yeast allergy, they should consult a doctor.

The controversial idea that some people are hypersensitive to yeast continues to influence alternative medicine. For very few people, however, yeast allergies can cause a range of symptoms. People who think they have either disorder should consult a doctor for testing.

Self-diagnosis of allergies can lead to unnecessary fear. A professional diagnosis may be necessary to prevent severe allergic reactions. If a person has a severe yeast allergy, they may need to carry an epinephrine injector.