Life Extension Magazine®

Woman affected by to seasonal allergies before taking probiotics

Battling Allergies with Probiotics

A specific probiotic combined with fermented yeast resulted in 43% fewer days with nasal congestion and a 31% reduction in eye symptoms.

Dr. Gary Gonzalez, MD, in August 2023. Written by: Michael Downey, Health & Wellness Author.

Runny noses. Itchy eyes. Sneezing. Congestion.

Millions of people suffer from seasonal allergies and turn to prescription and over-the-counter medications to find relief.

Scientists have discovered a surprising alternative approach: probiotics.

The idea of using helpful bacteria to reduce allergic symptoms may sound radical, but clinical trials show it to be quite beneficial.

What you need to know

  • Current medications for seasonal allergies target the symptoms, like sneezing, runny nose, and itchy eyes.
  • A novel approach focuses, instead, on the cause of allergies, restoring the normal balance between immune-system cells that promote allergic reactions and those that suppress them.
  • In a major advance for allergy sufferers, the probiotic Lactobacillus acidophilus L-92 and yeast fermentate demonstrate the ability to restore immune balance.
  • Human studies have shown that this "retraining" of the immune system substantially reduces the severity of allergic symptoms and the duration of seasonal allergies.

In one study, a specific probiotic, Lactobacillus acidophilus L-92, led to a 2.5-fold improvement in nasal allergy symptoms and a 4.7-fold improvement in eye symptoms compared to people using a placebo.1

Other trials show that a combination of L. acidophilus L-92 and fermented yeast result in:

  • 43% fewer days with nasal congestion
  • 24% reduction in swollen nasal passages
  • 31% reduction in eye symptoms2-4

These are significant findings for allergy sufferers.

A new combination of probiotic and fermented yeast works by targeting the root cause of allergies: an out-of-balance immune response.

Attacking the Cause of Allergies

Probiotics written on a clipboard

Allergies affect more than 50 million American adults every year.

They are the 6th leading cause of chronic illness in America, costing society more than $18 billion annually.5,6

An allergic reaction occurs when the immune system overreacts to something in the environment that is harmless to most people.

When the body perceives a threat from an allergen such as dust or pollen, it swings into defensive action. The result is watery eyes and a runny nose designed to flush the allergen out from the body.

These allergy symptoms are the last in a long, domino effect of reactions involving the body's immune-system cells.

Once an allergy attack occurs, most people reach for over-the-counter medications for relief. The problem is that antihistamines, steroids (like Flonase®), and decongestants, only provide temporary relief.

A better solution is to stop the body from overreacting to harmless threats like pollen or dust.

For that to happen we need to restore normal immune balance—and that involves retraining immune system cells in what's called the Th2 family.

Th2 cells are also known as T helper type 2 cells. Th2 cells play a role in organizing a protective immune response to outside invaders such as allergens.

Two ingredients have been identified, Lactobacillus acidophilus L-92 and yeast fermentate, that effectively retrain the immune system to take pollen and other allergens in stride and mute the excessive inflammatory responses that produce irritating allergy symptoms.

Regulating the Immune Response


Researchers sought to identify ingredients that would work on the cause of allergic reactions by reining in the immune system's Th2 cells.

Scientists in Japan and the U.S. uncovered 2 compounds that help restore normal Th2 balance. These 2 supplements, Lactobacillus acidophilus L-92 and yeast fermentate, reduce symptoms by lowering the allergic response to pollen and other allergens.

This group of scientists began investigating probiotics for allergy relief because they are essential for a healthy gut, where many of the body's immune cells reside.7

When researchers compared 12 different probiotic strains in a lab study, L. acidophilus L-92 stood out for its impact on seasonal allergies.8 Animal studies showed that this strain reduces levels of the inflammatory antibodies known as immunoglobulin E (which trigger the release of chemicals that cause an allergic reaction), reduces substances associated with Th2, and boosts cells associated with better immune balance.8,9

Similarly, a fermented form of baker's yeast (Saccharomyces cerevisiae) called yeast fermentate reduces IgE, providing additional allergy relief.10

As a result, these 2 ingredients can quell allergy symptoms without causing the side effects seen with anti-inflammatory, antihistamine, or decongestant drugs.

To validate that these immune-balancing effects beneficially impact allergies, scientists conducted studies on human volunteers.

Human Studies with L. acidophilus L-92

Woman holding a flower

First, researchers focused on the allergy benefits of Lactobacillus acidophilus L-92.

People allergic to Japanese cedar pollen, a potent allergen, were enlisted for a clinical study that covered 2 consecutive annual allergy seasons. They received either a placebo or L. acidophilus L-92.3

In the first allergy season, the Lactobacillus acidophilus L-92 treatment group showed a 31% reduction in the eye symptom/medication score, which indicated reduced experience of itchy or watery eyes and the need for less medication. This improved eye symptom/medication score was found again in the second allergy season. Researchers also found a trend towards improved scores for reduced swelling and color of membranes lining the nostrils.3 (Allergic mucous membranes appear pale, while healthy membranes are pink.)

In a second study, researchers gave either a placebo or L. acidophilus L-92, every day for 8 weeks, to 49 people with year-round hay fever, which can be more difficult to manage than seasonal allergies.2

They documented an approximate 28% improvement in nasal membrane color at week 6 and an approximate 24% improvement in nasal membrane color at week 8. Patient-reported symptom/medication scores fell, compared with placebo recipients, by about 19% after 8 weeks. There was also a trend towards improvement in eye symptoms, such as itchiness and redness.2

A third trial, lasting 8 weeks, demonstrated the ability of L. acidophilus L-92 to alleviate symptoms in people who did not start taking it until after they were exposed to the allergen. Eighty volunteers with cedar-pollen allergy were exposed to this pollen for 3 hours before receiving the probiotic. The results were astonishing: Treated individuals demonstrated a 2.5-fold improvement in nasal symptoms and a 4.7-fold improvement in eye symptoms compared with placebo subjects.1

In several other studies, scientists found that L. acidophilus L-92 also has a favorable effect on eczema (atopic dermatitis), a condition closely related to seasonal allergies. This form of allergic response is characterized by itchy, scaly, oozing lesions on the skin, and can affect the skin on any part of the body. Taking this probiotic was shown to reduce symptom scores for eczema by more than 50%11,12 and to help reduce the spread of eczema from one part of the body to another.13

Taken together, these findings demonstrate significant reductions in symptoms of seasonal and year-round allergies.

Human Studies with Yeast Fermentate

Scientists also performed clinical studies with yeast fermentate.

Researchers conducted a pilot study on 25 healthy individuals, giving them either a placebo or 500 mg of dried yeast fermentate daily for 5 weeks during the beginning of the allergy season.10

The placebo treatment had no effect. But half of the treated male volunteers reported a complete absence of allergy symptoms, which fully returned 1-2 weeks after they stopped taking the supplement.

Antibodies called IgE are one of the causes of hay fever symptoms. Based on this study, researchers surmised that yeast fermentate helps reduce IgE.

IgE causes the body to release chemicals (like histamines) that cause an allergic reaction and produce symptoms that can affect the eyes, nose, throat, lungs, or skin.

Over the course of this 5-week study, as the allergy season went into full swing, blood levels of IgE steadily increased among placebo recipients indicating heightened allergic responses.

In those subjects taking the yeast fermentate, IgE levels barely changed, indicating a reduced allergic reaction. The conclusion from this study is that yeast fermentate calms allergic responses by stabilizing IgE levels.10

A larger clinical study was then undertaken, with 96 people who had a documented history of seasonal allergies and hay fever. During the highest pollen-count portion of the year, participants took either a placebo or 500 mg of dried yeast fermentate once daily.4

The first 6 weeks of the 12-week study took place during the highest pollen-count period. During this time, scientists documented a reduction in the severity of runny nose and nasal congestion in the treatment group.

Compared to a placebo group, the supplemented subjects experienced 43% fewer total days with nasal congestion. By the end of the study, they also showed decreased levels of white blood cells in their nasal mucus, indicating reduced activation of allergy-triggering cells.4

These clinical effects deliver clear and substantial quality-of-life improvements for those who suffer from seasonal allergies.

The Risks of Allergy Medications
Woman refusing medication

During allergy season, people resort to an assortment of over-the-counter medications such as antihistamines, steroids, and decongestants.

To alleviate symptoms, these drugs are intended to block the histamines and suppress the inflammation that produce runny noses, and watery eyes.

But allergy medications come with many potential side effects, including drowsiness, constipation, headache, rapid heartbeat, and sleep problems.14 In fact, drugs from the category called anticholinergics — which includes some commonly used anti-allergy medications like diphenhydramine (Benadryl®) — have been associated with a potentially increased risk of Alzheimer's disease.15

Here is a list of possible side effects:14


Drowsiness, dry mouth/nose/throat, stomach problems, blurred vision, and constipation.

Examples: Benadryl®, Claritin®, Zyrtec®, Allegra®, Claritin Eye® (eye drops)

Nasal corticosteroids:

Nasal dryness/irritation, nosebleeds, throat irritation, headache, nausea, vomiting, cough, and (with long-term use) fungal infections of the throat, immune suppression.

Examples: Flonase® (nasal), Nasacort® (nasal)

Mast cell stabilizers:

Stinging sensation inside the nose.

Examples: Alomide® (eye drops), Intal® (inhaler), Nasalcrom® (nasal)

Leukotriene inhibitors:

Weakness, upset stomach, earache, dizziness, cough, headache, trouble sleeping, and (less likely) flu-like symptoms.

Example: Singulair®

Nasal decongestants:

Burning/stinging/dryness in the nose, runny nose, and sneezing.

Example: Afrin®

Oral decongestants:

Dizziness, headache, nervousness, fast heartbeat, increased blood pressure, loss of appetite, and problems sleeping.

Example: Sudafed®

Nasal anticholinergics:

Bloody/dry nose, nasal congestion, dry mouth, bad taste in the mouth, irritated throat, dizziness, and nausea.

Example: Atrovent®

Topical corticosteroids (for skin allergies):

Burning, itching, redness, changes to skin color, and thinning of skin.

Example: Cortaid®

Topical immunomodulators (for skin allergies):

Stinging, burning, irritation, itching at the application site, and possibly headache and flu symptoms.

Example: Protopic® ointment


Mainstream allergy medications target symptoms, not the root cause of the problem, and come with an array of potential side effects.

Scientists have identified 2 ingredients that retrain the immune system not to overreact to pollen and other allergens, muting the excessive inflammatory responses behind allergy symptoms.

In human studies, the probiotic Lactobacillus acidophilus L-92 and yeast fermentate substantially reduced seasonal allergy symptoms, such as swollen nasal passages and eye irritation, and resulted in 43% fewer days with nasal congestion.

These two supplements provide a unique option for improving the quality of life in allergy sufferers.

If you have any questions on the scientific content of this article, please call a Life Extension® Wellness Specialist at 1-866-864-3027.


  1. Enomoto MI, T; Take, CR; et. al. . Effects of oral ingestion of L. acidophilus GRAS L. acidophilus L-92 strain on the cedar pollen allergy - Verification of preventive action in artificial exposure facility. The 56th Annual Meeting of the Japanese Society of Allergology, Tokyo, Japan. 2006.
  2. Ishida Y, Nakamura F, Kanzato H, et al. Clinical effects of Lactobacillus acidophilus strain L-92 on perennial allergic rhinitis: a double-blind, placebo-controlled study. J Dairy Sci. 2005 Feb;88(2):527-33.
  3. Ishida Y, Nakamura F, Kanzato H, et al. Effect of milk fermented with Lactobacillus acidophilus strain L-92 on symptoms of Japanese cedar pollen allergy: a randomized placebo-controlled trial. Biosci Biotechnol Biochem. 2005 Sep;69(9):1652-60.
  4. Moyad MA, Robinson LE, Kittelsrud JM, et al. Immunogenic yeast-based fermentation product reduces allergic rhinitis-induced nasal congestion: a randomized, double-blind, placebo-controlled trial. Adv Ther. 2009 Aug;26(8):795-804.
  5. Available at: Accessed March 26, 2018.
  6. Available at: Accessed March 26, 2018.
  7. Furness JB, Kunze WA, Clerc N. Nutrient tasting and signaling mechanisms in the gut. II. The intestine as a sensory organ: neural, endocrine, and immune responses. Am J Physiol. 1999 Nov;277(5):G922-8.
  8. Ishida Y, Bandou I, Kanzato H, et al. Decrease in ovalbumin specific IgE of mice serum after oral uptake of lactic acid bacteria. Biosci Biotechnol Biochem. 2003 May;67(5):951-7.
  9. Torii A, Torii S, Fujiwara S, et al. Lactobacillus Acidophilus strain L-92 regulates the production of Th1 cytokine as well as Th2 cytokines. Allergol Int. 2007 Sep;56(3):293-301.
  10. Jensen GS, Patterson, K.M., Barnes, J., Schauss, A.G., Beaman, R., Reeves, S.G. and Robinson, L.E.,. A double-blind placebo-controlled, randomized pilot study: consumption of a high-metabolite immunogen from yeast culture has beneficial effects on erythrocyte health and mucosal immune protection in healthy subjects. The Open Nutrition Journal. 2008;2:pp.68-75.
  11. Torii S, Torii A, Itoh K, et al. Effects of oral administration of Lactobacillus acidophilus L-92 on the symptoms and serum markers of atopic dermatitis in children. Int Arch Allergy Immunol. 2011;154(3):236-45.
  12. Yamamoto K, Yokoyama K, Matsukawa T, et al. Efficacy of prolonged ingestion of Lactobacillus acidophilus L-92 in adult patients with atopic dermatitis. J Dairy Sci. 2016 Jul;99(7):5039-46.
  13. Inoue Y, Kambara T, Murata N, et al. Effects of oral administration of Lactobacillus acidophilus L-92 on the symptoms and serum cytokines of atopic dermatitis in Japanese adults: a double-blind, randomized, clinical trial. Int Arch Allergy Immunol. 2014;165(4):247-54.
  14. Available at: Accessed February 13, 2019.
  15. Gray SL, Anderson ML, Dublin S, et al. Cumulative use of strong anticholinergics and incident dementia: a prospective cohort study. JAMA Intern Med. 2015 Mar;175(3):401-7.