Allergies

Table of Contents

1. How Allergies Work
2. Common Types of Allergies
3. Common Symptoms of Allergies
4. Causes and Risk Factors
5. Diagnosis
6. Treatment Options
7. Prevention and Management Strategies
8. Complications of Allergies
9. Key Research Papers
10. Connections
11. Featured Videos

How Allergies Work

Allergies occur when the immune system reacts to a foreign substance, such as pollen, pet dander, certain foods, or medication, as if it were a threat. These substances, known as allergens, trigger the immune response, which can cause various symptoms ranging from mild to severe.

In the quick type of allergy, the body first makes allergy antibodies (immunoglobulin E, IgE) against the allergen. These antibodies sit on mast cells, immune cells found in the skin, nose, airways and gut. When the allergen comes back and binds to these antibodies, the mast cell bursts open and releases histamine and other chemicals, which cause the itching, swelling, sneezing and hives. A 2012 review by Galli and Tsai describes these antibodies and mast cells as the main drivers of anaphylaxis and other sudden allergic reactions, and also of the long-lasting inflammation and airway changes seen in asthma.

Common Types of Allergies

1. Seasonal Allergies (Hay Fever)

• Caused by: Pollen from trees, grasses, and weeds.
• Symptoms: Sneezing, runny or stuffy nose, itchy eyes, and sore throat.

2. Food Allergies

• Common triggers: Peanuts, tree nuts, shellfish, milk, eggs, wheat, soy, fish, and sesame. Under the US FASTER Act, sesame became the ninth major food allergen, and since January 1, 2023 it must be labeled as an allergen on packaged foods and dietary supplements (US Food and Drug Administration).
• Symptoms: Hives, swelling, stomach pain, vomiting, and in severe cases, anaphylaxis.

3. Drug Allergies

• Caused by: Reactions to medications such as penicillin and other antibiotics, or aspirin and other pain relievers.
• Symptoms: Rash, itching, swelling, and breathing difficulties.

4. Insect Sting Allergies

• Caused by: Stings from bees, wasps, hornets, or fire ants.
• Symptoms: Redness, swelling at the sting site, and in severe cases, anaphylaxis.

5. Skin Allergies

• Includes: Eczema, contact dermatitis, and hives.
• Caused by: Contact with allergens such as latex, certain metals, or cosmetics.

Common Symptoms of Allergies

• Runny or stuffy nose
• Itchy or watery eyes
• Sneezing
• Hives or skin rash
• Swelling: Often in the face, lips, or tongue.
• Shortness of breath or wheezing
• Stomach cramps, nausea, or diarrhea
• Anaphylaxis: A severe, life-threatening reaction that requires immediate medical attention.

Causes and Risk Factors

• Genetic predisposition: Allergies often run in families.
• Environmental exposure: Repeated exposure to allergens can trigger an immune response.
• Asthma and other conditions: People with asthma or other allergic conditions are more likely to develop allergies.

Diagnosis

• Medical history and symptom assessment
• Skin prick test: A small amount of allergen is applied to the skin to check for a reaction.
• Blood tests: To measure levels of allergen-specific antibodies (immunoglobulin E).
• Elimination diet: To identify food allergies by removing potential triggers and reintroducing them one by one.

Treatment Options

• Medications:
  • Antihistamines: To relieve sneezing, itching, and runny nose.
  • Decongestants: To reduce nasal congestion.
  • Corticosteroids: Nasal sprays or creams to reduce inflammation.
  • Epinephrine auto-injectors: For emergency treatment of anaphylaxis.
  • Omalizumab (an anti-IgE injection): In a 2024 trial in 177 children and teenagers aged 1 to 17 with several food allergies, 67% of those given omalizumab injections for 16 to 20 weeks could eat at least 600 mg of peanut protein in one dose without a dose-limiting reaction, against 7% on placebo (cashew 41% vs 3%, milk 66% vs 10%, egg 67% vs 0%). The trial describes this as raising the amount of food that sets off a reaction, not as a cure.
• Immunotherapy:
  • Allergy shots: Gradually introduce small doses of allergens to build tolerance.
  • Sublingual tablets: Taken under the tongue to reduce allergic reactions over time.
• Avoidance:
  • Reducing contact with triggers: Reducing contact with known allergens is the main non-drug approach described in allergy guidance.

Prevention and Management Strategies

• Closed windows: Closing windows during allergy seasons keeps pollen from entering the home.
• Air purifiers: Air purifiers filter allergens from indoor air.
• Showering and changing clothes after time outdoors removes pollen and other allergens from skin, hair and clothing.
• A clean home: Regular washing of bedding, vacuuming with a HEPA filter, and less dust and mold reduce indoor allergens.
• Epinephrine auto-injector: People with severe allergies at risk of anaphylaxis are prescribed an epinephrine auto-injector to carry with them.
• Early peanut in high-risk babies: The LEAP trial randomly assigned 640 babies aged 4 to 11 months with severe eczema, egg allergy, or both to eat or avoid peanut until age 5. Among babies with a negative skin-prick test at the start, peanut allergy at age 5 was 13.7% in the avoiding group and 1.9% in the eating group; among those with a small positive skin test, it was 35.3% and 10.6%.

Complications of Allergies

• Anaphylaxis: A severe, life-threatening allergic reaction.
• Asthma: Allergies can trigger or worsen asthma symptoms.
• Chronic sinusitis: Persistent inflammation of the nasal passages.
• Skin infections: Resulting from scratching due to allergic skin reactions.

Key Research Papers

1. Pawankar R, et al. Allergic diseases and asthma: a global public health concern and a call to action. World Allergy Organization Journal. 2014;7(1):12. — doi:10.1186/1939-4551-7-12
2. Galli SJ, Tsai M. IgE and mast cells in allergic disease. Nature Medicine. 2012;18(5):693-704. — doi:10.1038/nm.2755
3. Bousquet J, et al. Allergic Rhinitis and its Impact on Asthma (ARIA) 2008 update. Allergy. 2008;63(Suppl 86):8-160. — PubMed PMID: 18331513
4. Sicherer SH, Sampson HA. Food allergy: epidemiology, pathogenesis, diagnosis, and treatment. Journal of Allergy and Clinical Immunology. 2014;133(2):291-307. — doi:10.1016/j.jaci.2013.11.020
5. Du Toit G, et al. Randomized trial of peanut consumption in infants at risk for peanut allergy (LEAP study). New England Journal of Medicine. 2015;372(9):803-813. — doi:10.1056/NEJMoa1414850
6. Sampson HA, et al. Food allergy: a practice parameter update-2014. Journal of Allergy and Clinical Immunology. 2014;134(5):1016-1025.e43. — PubMed PMID: 25174862
7. Durham SR, et al. Long-term clinical efficacy of grass-pollen immunotherapy. New England Journal of Medicine. 1999;341(7):468-475. — doi:10.1056/nejm199908123410702
8. Holgate ST. The epidemic of allergy and asthma. Nature. 1999;402(6760 Suppl):B2-B4. — doi:10.1038/35037000
9. Platts-Mills TAE. The allergy epidemics: 1870-2010. Journal of Allergy and Clinical Immunology. 2015;136(1):3-13. — doi:10.1016/j.jaci.2015.03.048
10. Lieberman P, et al. The diagnosis and management of anaphylaxis practice parameter: 2010 update. Journal of Allergy and Clinical Immunology. 2010;126(3):477-480. — doi:10.1016/j.jaci.2010.06.022
11. Muraro A, et al. EAACI food allergy and anaphylaxis guidelines: diagnosis and management of food allergy. Allergy. 2014;69(8):1008-1025. — doi:10.1111/all.12429
12. Wood RA, Togias A, Sicherer SH, et al. Omalizumab for the Treatment of Multiple Food Allergies. New England Journal of Medicine. 2024;390(10):889-899. — PubMed PMID: 38407394
13. US Food and Drug Administration. The FASTER Act: Sesame Is the Ninth Major Food Allergen. — fda.gov

Historical Background

The concept of allergy was first introduced by Clemens von Pirquet in 1906, who coined the term to describe altered immune reactivity. Charles Richet discovered anaphylaxis in 1902, for which he received the Nobel Prize in 1913. The role of immunoglobulin E (IgE) in allergic responses was independently discovered by Kimishige Ishizaka and Gunnar Johansson in 1966-1967, establishing the modern immunological basis of allergic disease.

PubMed Topic Searches

Explore current literature on allergies via PubMed topic searches. These links open live PubMed searches for the listed keywords — results update as new studies are indexed.

1. Clinical trials on allergic rhinitis — PubMed search
2. Clinical trials on food allergy — PubMed search
3. Clinical trials on anaphylaxis — PubMed search
4. Clinical trials on allergen immunotherapy — PubMed search
5. Clinical trials on atopic dermatitis allergy — PubMed search
6. Clinical trials on omalizumab allergy — PubMed search
7. Clinical trials on IgE-mediated hypersensitivity — PubMed search

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Connections

• Pain & Allergy
• Asthma: What Happens in an Attack — interactive animation
• Histamine, Mast Cells & Allergy — interactive animation
• Asthma
• Eczema
• Mast Cell Activation Syndrome
• Alpha-Gal Syndrome
• Food Intolerance
• Sinusitis
• Celiac Disease
• Hives and Flushing
• Chronic Cough
• Elimination Diet
• Shortness of Breath
• Yellow 5 Tartrazine
• Food Additives
• Chronic Pain
• Inflammatory Bowel Disease
• Hashimoto's Thyroiditis
• Quercetin
• Milk
• Common Cold
• Ear Infections
• Genetic Susceptibility to Vaccine Adverse Reactions — the immunoglobulin E mechanisms underlying excipient anaphylaxis
• Herbs covered on this site that discuss this condition: Perilla (Perilla frutescens) · Blessed Thistle · Echinacea (Echinacea purpurea) · Elecampane · Yarrow · Chrysanthemum (Chrysanthemum morifolium)
• Vitamin C
• Nettle

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