Allergies: Types, Symptoms, Causes and Treatment Info
Author: Disabled World (DW)
Updated/Revised Date: 2 Nov 2026
Table of Contents:
Synopsis - Definition - About This Section - FAQs - Publications - Subtopics
Synopsis
Learn about allergy types, symptoms, causes and treatments, including airborne allergens, the role of histamine and vitamins that may ease reactions.
At a Glance
- 1 - Histamine is released by mast cells when an allergen binds to the antibody IgE.
- 2 - Poison ivy rash is a delayed allergic reaction caused by T cells, not antibodies.
- 3 - Saline nasal rinsing has the best evidence among complementary approaches for hay fever.
- 4 - Raw butterbur contains chemicals that can damage the liver, so only certified products should be considered.
Topic Definition
- Allergy
An allergy is a hypersensitivity disorder in which the immune system overreacts to a normally harmless substance, treating it as a threat and mounting a defensive response. When the body encounters one of these triggers, known as an allergen, it can release large amounts of histamine and other chemicals that inflame surrounding tissue, producing familiar symptoms such as sneezing, a runny or stuffy nose, red and watery eyes, itching, hives, eczema, or, in the case of asthma, difficulty breathing. Common allergens include pollen, mold, dust, animal dander, insect stings, and certain foods, and reactions range from mildly annoying to, in rare and severe cases, a life threatening emergency called anaphylaxis. Because each person's immune system and biology differ, allergies vary widely in their triggers, severity, and in how well they respond to treatments such as antihistamines.
Overview
NOTE: This section is mainly on respiratory system allergies - For food allergy information, click here.
An allergy is a reaction of the immune system to a substance that is usually harmless, such as pollen, dust mites, mold, pet dander, insect stings, certain foods, or some medicines. These substances are called allergens. Symptoms range from sneezing, a runny or stuffy nose, and itchy, watery eyes to hives, eczema, and asthma attacks. In some people, a severe reaction called anaphylaxis affects the whole body and can be life-threatening; foods, insect stings, and medicines are the most common causes. Not every reaction or intolerance is an allergy.
Allergies are very common. In 2024, 31.7 percent of U.S. adults and 29.5 percent of children had at least one diagnosed allergy, and seasonal allergies such as hay fever affected 25.2 percent of adults [Centers for Disease Control and Prevention, n.d.].
How an Allergic Reaction Happens
The first time a person who is prone to allergies meets an allergen, the immune system makes an antibody called immunoglobulin E (IgE) against it. IgE attaches to mast cells in the nose, eyes, lungs, skin, and gut. When the allergen appears again, it binds to the IgE, and the mast cells release histamine and other chemicals. These chemicals cause the swelling, itching, mucus, and tightening of the airways that people feel as allergy symptoms [MedlinePlus, n.d.]. A tendency to develop allergies often runs in families.
Airborne Allergies and Their Symptoms
Airborne allergies are the most common type. Pollen from trees, grasses, and weeds causes seasonal allergic rhinitis, often called hay fever, while dust mites, mold, cockroaches, and pet dander can cause symptoms all year. Common symptoms include sneezing, a runny or blocked nose, itchy eyes, nose, and throat, coughing, postnasal drip, and red, watery, or swollen eyes (allergic conjunctivitis). Allergies can also trigger asthma attacks in people who have asthma.
Types of Allergic Reactions
Doctors describe four main types of hypersensitivity reactions. The most familiar, type I, is the immediate IgE reaction behind hay fever, food allergies, insect sting allergies, and anaphylaxis. Types II and III involve other antibodies that attack the body's own cells or form clumps in the blood and tissues. Type IV is a delayed reaction caused by T cells rather than antibodies; the itchy rash that appears a day or two after touching poison ivy is a common example.
Diagnosing Allergies
A doctor or allergist diagnoses allergies from a person's symptoms and history, often confirmed with skin prick tests or blood tests that measure IgE to specific allergens. Keeping a record of when and where symptoms happen can help identify triggers.
Treating Allergy Symptoms
The first step is to avoid known allergens where possible, for example by keeping windows closed on high-pollen days, using dust mite covers on bedding, controlling humidity to limit mold, and keeping pets out of the bedroom. Medicines include antihistamines, nasal corticosteroid sprays, decongestants, leukotriene modifiers, and allergy eye drops, and many are available without a prescription. Allergy shots or tablets placed under the tongue (allergen immunotherapy) can reduce symptoms over the long term for people allergic to pollen, dust mites, and some other allergens. People at risk of anaphylaxis should carry epinephrine, which can be given with an auto-injector or, since 2024, a nasal spray. Because people respond differently to treatment, it helps to work with a health care provider to find the right approach.
Vitamins, Supplements, and Other Complementary Approaches
Many vitamins, supplements, and herbal blends are sold for allergy relief, but for most of them there is little good evidence. The National Center for Complementary and Integrative Health (NCCIH) reports that saline nasal irrigation, rinsing the nose with a saltwater solution, has the best evidence among complementary approaches: a 2012 review of 10 studies found that regular rinsing for up to seven weeks eased nasal symptoms and reduced the use of allergy medicines in adults and children [National Center for Complementary and Integrative Health, n.d.]. Rinsing devices should be used only with distilled, sterile, or boiled and cooled water, because unfiltered tap water can contain harmful organisms.
A few rigorous trials suggest that butterbur leaf extract may ease hay fever symptoms, but raw butterbur contains chemicals called pyrrolizidine alkaloids that can damage the liver, so only products certified free of them should be considered, and only with a doctor's advice. There is no convincing evidence that honey relieves seasonal allergies [National Center for Complementary and Integrative Health, n.d.]. Quercetin, vitamin C, vitamin E, other antioxidants, glucosamine, and herbal blends sold for allergies have not been shown in good-quality studies to treat allergy symptoms. Supplements can interact with medicines, and high doses of some vitamins, such as vitamin A, can be harmful, so it is best to talk with a health care provider before trying them.
Allergy Facts and Statistics
- Percent of adults with any diagnosed allergy: 31.7% (2024).
- Percent of adults with a seasonal allergy: 25.2% (2024).
- Percent of adults with eczema: 7.7% (2024).
- Percent of adults with a food allergy: 6.7% (2024).
- Percent of children with any diagnosed allergy: 29.5% (2024).
- Percent of children with a seasonal allergy: 20.6% (2024).
- Percent of children with eczema: 12.7% (2024).
- Percent of children with a food allergy: 5.3% (2024).
Frequently Asked Questions
What is the difference between an allergy and an intolerance?
An allergy involves the immune system reacting to a substance, while an intolerance is usually a digestive or chemical response that does not involve the immune system.
How are allergies diagnosed?
Doctors often use skin prick tests, blood tests that measure specific antibodies, and a review of symptoms and history to identify triggers.
Can allergies develop later in life?
Yes, allergies can appear at any age, and some people develop new sensitivities as adults even to things that never troubled them before.
What is anaphylaxis and how is it treated?
Anaphylaxis is a severe, rapid, and potentially life threatening allergic reaction that is treated with emergency adrenaline and urgent medical care.
Are allergies hereditary?
A tendency toward allergies often runs in families, though the specific allergens a person reacts to can differ from those of their relatives.
Can you outgrow an allergy?
Some childhood allergies, particularly to certain foods such as milk or egg, may fade with age, while others can persist for life.
How can I reduce allergens in my home?
Regular cleaning, washing bedding in hot water, using dust mite covers, controlling humidity to limit mold, and keeping pets out of bedrooms can all help.
What is allergy immunotherapy?
Allergy immunotherapy uses regular allergy shots or tablets under the tongue to slowly train the immune system to tolerate an allergen such as pollen or dust mites. Treatment usually lasts three to five years and can reduce symptoms long term.
References
- Centers for Disease Control and Prevention. (n.d.). FastStats: Allergies and hay fever.
- MedlinePlus. (n.d.). Allergy. National Library of Medicine.
- National Center for Complementary and Integrative Health. (n.d.). Seasonal allergies and complementary health approaches: What the science says.
Curated and edited by Ian C. Langtree, Founder and Editor-in-Chief, Disabled World. This section is maintained by the Disabled World editorial team. Last updated: