Gut Health and Allergies: What You Need to Know
How gut health and allergies are connected
Researchers think the microbes in your gut help train the immune system, and that this training may affect whether it overreacts to harmless things such as foods or pollen. The link is strongest in early childhood, and most of the evidence comes from observational and animal studies. No diet or probiotic has been shown to make an existing allergy go away, and this article is general information, not medical advice.
What an allergy is, and what it isn’t
An allergy is an immune system reaction. In a person with a food allergy, the immune system reacts abnormally to part of a food, and the reaction can sometimes be severe and life-threatening, according to the National Institute of Allergy and Infectious Diseases (NIAID). NIAID says food allergy affects about 8 percent of children and nearly 11 percent of adults in the United States.
A food intolerance is different. The NHS explains that intolerance tends to cause gut symptoms such as diarrhea, bloating, gas and tummy pain, while allergy causes symptoms such as itchy skin, wheezing or swelling of the lips, face and eyes. Lactose intolerance is a good example. The NIDDK notes that lactose intolerance comes from trouble digesting milk sugar, while milk allergy is an immune response to milk proteins and can be life-threatening.
The difference matters here. Many people with gut symptoms after eating suspect an allergy, but a gut-friendly diet that might ease an intolerance does nothing to make a true allergy safe.
Why the gut matters to the immune system
Microbes help teach tolerance
Your gut is one of the main places where the immune system meets material from the outside world, from food to bacteria. Some gut microbes seem to encourage regulatory T cells, a type of immune cell that calms unneeded reactions. In a 2011 mouse study in Science, certain Clostridium bacteria boosted these cells in the colon, and giving the bacteria early in life reduced allergy-type antibody responses later. That is animal research, and it does not show the same thing happens in people.
The “hygiene hypothesis”
The NCCIH describes the idea that modern lifestyles may have reduced contact with microbes early in life, and that this may have contributed to the rise in allergies. It adds that factors unrelated to hygiene, such as smaller family size and antibiotic use, may also play a role. It is an idea that fits much of the data, not a proven cause.
Early-life gut microbes and later allergy
Several studies in children point the same way, though none prove cause and effect:
- Milk allergy: in a 2016 study of 226 infants with milk allergy, gut microbe makeup at 3 to 6 months was linked with whether the allergy resolved by age 8. Children whose allergy went away had more Clostridia and Firmicutes bacteria.
- Asthma: a Danish study of 690 children found that 1-year-olds with a less mature gut microbiome had a higher risk of asthma at age 5, but only among children whose mothers had asthma.
These are observational studies. They show a link, and other factors such as birth method, feeding and antibiotics may explain part of it.
What the research says about probiotics and allergy
Probiotics are the most tested way to act on this idea. The NCCIH has summarized the reviews:
| Use | What reviews found | Strength |
|---|---|---|
| Preventing eczema (probiotics in pregnancy or early infancy) | Lower risk of atopic dermatitis in 17 studies with 4,755 participants, especially with probiotic mixtures | Moderate, for eczema only |
| Preventing asthma, wheezing or hay fever | No effect seen in the same review | No benefit shown |
| Treating hay fever | Some evidence of better symptoms in 23 studies with 1,919 people, but products varied too much for a recommendation | Weak to mixed |
| Treating asthma in children | Inconclusive in 11 studies with 910 children | Unclear |
| Treating eczema in children | No consistent benefit in 13 studies with 1,271 children | Not supported |
The pattern is that some probiotics, given early, may slightly lower the risk of eczema, but they have not been shown to prevent or treat food allergies. Effects also depend on the exact strain, so results from one product don’t carry over to another. You can read more in our guides to eczema and gut health and probiotics for immune support.
Probiotics are not risk-free for everyone. The NCCIH notes that the risk of harm is higher in people with severe illness or weak immune systems, and that severe or fatal infections have been reported in premature infants given probiotics. Talk with a doctor before giving probiotics to a baby, and before taking them if you are pregnant, immunocompromised or seriously ill.
The one gut-related step with strong evidence
The best evidence for preventing a food allergy is not about microbes at all. It is about feeding allergenic foods early. In the LEAP trial, 640 high-risk infants with severe eczema, egg allergy or both were assigned to eat or avoid peanut until age 5. Among infants who first tested negative, peanut allergy at age 5 was 1.9 percent in the eating group and 13.7 percent in the avoidance group. NIAID’s food allergy guidelines page describes this as an 81 percent relative reduction and the basis for updated U.S. peanut guidelines.
High-risk babies may need testing before peanut is introduced, so this is a conversation to have with your pediatrician, not a step to take alone.
Practical steps for gut health if you have allergies
General gut-friendly habits are reasonable for most people, as long as they avoid foods you react to:
- Eat a range of fiber-rich plants: vegetables, fruit, beans, oats and whole grains feed gut microbes.
- Include fermented foods you tolerate: in a small 17-week Stanford study, a diet high in fermented foods raised gut microbe diversity and lowered several inflammation markers in healthy adults. It did not test allergy outcomes. Our guide to fermented foods for gut health covers options.
- Watch for hidden allergens: yogurt and kefir are made from milk, so they are not safe for people with milk allergy. Look at non-dairy probiotic foods instead, and check labels for other allergens.
- Use antibiotics only when needed: follow your doctor’s advice, and see our guide on restoring gut health after antibiotics.
- Don’t self-treat a suspected allergy: elimination diets, home tests and supplements can miss a real allergy or cut out foods you don’t need to avoid.
When to see a doctor
See a doctor if you or your child have symptoms after eating that keep coming back, if you suspect a food allergy, or before introducing allergenic foods to a high-risk baby. Common food allergy symptoms listed by the NHS include itchy skin or hives, swelling of the lips, face and eyes, coughing or wheezing, and feeling dizzy.
Call 911 or your local emergency number right away if someone has signs of anaphylaxis, a severe reaction the NHS describes as life-threatening and fast:
- Swelling of the lips, mouth, throat or tongue
- Fast breathing, wheezing or struggling to breathe
- A tight throat or trouble swallowing
- Skin, lips or tongue turning blue, gray or pale
- Feeling faint, confused or collapsing
The NHS advises using an adrenaline (epinephrine) auto-injector if you have one, then calling for an ambulance.
Related topics
- Kids’ Gut Health: how a child’s gut develops and what supports it.
- Eczema and Gut Health: the skin side of the same immune story.
- Gut Health and Inflammation: how gut microbes relate to inflammation.
- Probiotics for Immune Support: what probiotic research shows for immunity.
- Is Greek Yogurt Lactose Free?: for people with lactose intolerance rather than milk allergy.
Sources
- Food Allergy (National Institute of Allergy and Infectious Diseases)
- Guidelines for Clinicians and Patients for Diagnosis and Management of Food Allergy in the United States (NIAID)
- Food intolerance (NHS)
- Food allergy (NHS)
- Anaphylaxis (NHS)
- Symptoms & Causes of Lactose Intolerance (National Institute of Diabetes and Digestive and Kidney Diseases)
- Probiotics: Usefulness and Safety (National Center for Complementary and Integrative Health)
- Atarashi K, et al. Induction of colonic regulatory T cells by indigenous Clostridium species (Science, 2011)
- Bunyavanich S, et al. Early-life gut microbiome composition and milk allergy resolution (Journal of Allergy and Clinical Immunology, 2016)
- Stokholm J, et al. Maturation of the gut microbiome and risk of asthma in childhood (Nature Communications, 2018)
- Du Toit G, et al. Randomized trial of peanut consumption in infants at risk for peanut allergy (New England Journal of Medicine, 2015)
- Wastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status (Cell, 2021)
This article is for general information and is not medical advice. Talk to your doctor or a registered dietitian before changing your diet, supplements or medication, especially if you have a health condition.
