Allergy
An exaggerated immune response to harmless substances.
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An allergy is an exaggerated immune response where the body mistakenly identifies an ordinarily harmless allergen as a threat. Allergic reactions give rise to allergic diseases such as hay fever, allergic conjunctivitis, allergic asthma, atopic dermatitis, food allergies, and anaphylaxis. Allergies are common, affecting about 20% of people in the developed world with allergic rhinitis, and rates of many allergic diseases appear to be increasing.
- Common allergens
- Pollen, certain foods, metals, insect stings, medications, latex
- Affected population (allergic rhinitis)
- About 20% in developed world
- Affected population (food allergy)
- 10% of adults, 8% of children
- Affected population (atopic dermatitis)
- About 20% have or have had
- Affected population (asthma)
- About 1–18% depending on country
- Affected population (anaphylaxis)
- 0.05–2%
Lore & Background
The development of allergies is due to genetic and environmental factors. The mechanism of allergic reactions involves immunoglobulin E antibodies (IgE) binding to an allergen and then to a receptor on mast cells or basophils, where they trigger the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person's medical history, with further testing of the skin or blood possibly useful in certain cases, though positive tests may not necessarily mean there is a significant allergy.
Reader's Guide
Allergies are significant because they affect a large portion of the population and can range from mild symptoms like sneezing and itchy skin to life-threatening anaphylaxis. Treatments include avoidance of known allergens, medications such as steroids and antihistamines, and injectable adrenaline (epinephrine) for severe reactions. Allergen immunotherapy, which gradually exposes people to larger amounts of allergen, is useful for some types such as hay fever and reactions to insect bites, though its use in food allergies is unclear. Early exposure of children to potential allergens may be protective. The intestinal microbiome is increasingly recognized as an important factor in allergy development, with early-life alterations in microbiota composition associated with increased risk of food allergy and atopic disease.
Did You Know?
- Anaphylaxis occurs in between 0.05–2% of people, depending on the country.
- Early exposure of children to potential allergens may be protective against allergies.
- Allergen immunotherapy is useful for hay fever and reactions to insect bites, but its use in food allergies is unclear.
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Frequently Asked Questions
What is Allergy?
Allergy is the body's immune system mounting an outsized defensive attack against a substance that is actually harmless, such as pollen, a food protein, or a medication. Instead of ignoring the trigger, the immune machinery flags it as a dangerous invader and launches a reaction far beyond what the situation warrants.
What are Allergy's known manifestations?
Depending on which organ system is targeted, Allergy can present as hay fever, allergic conjunctivitis, allergic asthma, atopic dermatitis, food allergy reactions, or the life-threatening systemic episode known as anaphylaxis. Each manifestation reflects the same underlying overreaction but expressed through different tissues and symptoms.
How widespread is Allergy's influence?
Roughly one in five people in developed nations experience allergic rhinitis, while food allergies affect about 10% of adults and 8% of children. Asthma prevalence ranges from 1% to 18% depending on the country, and anaphylaxis is reported in somewhere between 0.05% and 2% of the population.
What are the most common triggers Allergy reacts to?
The most frequently encountered allergens include airborne pollen, specific foods, metals, insect stings, certain medications, and latex. The immune system misreads any of these ordinarily benign substances as a threat and orchestrates the exaggerated response.
Why is Allergy considered significant in modern medicine?
Allergic diseases are among the most prevalent chronic conditions in the developed world, and their incidence appears to be climbing year over year. Because they range from mildly irritating to immediately fatal, they carry a substantial burden on public health systems and on individual quality of life.
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