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Understanding Allergies

Allergies occur when your immune system reacts to a substance that is usually harmless to most people. Learn about the science behind allergic reactions, why they happen, and what factors can increase your risk.

The Basics

What is an Allergy?

An allergy is an overreaction of the immune system to substances that are typically harmless to most people. These substances are called allergens.

When someone with an allergy encounters an allergen, their immune system treats it as a threat and launches a defensive response. This response causes the release of chemicals like histamine, which trigger the symptoms we recognize as an allergic reaction.

Allergic reactions can range from mild (sneezing, itchy eyes) to severe and life-threatening (anaphylaxis). The type and severity of symptoms depend on the allergen, how you were exposed, and your individual immune response.

Key Terms

Allergen

A substance that triggers an allergic reaction. Common allergens include pollen, certain foods, and insect venom.

Antibodies (IgE)

Proteins produced by the immune system to identify and neutralize foreign substances. IgE antibodies are specifically involved in allergic reactions.

Histamine

A chemical released during an allergic reaction that causes many allergy symptoms like itching, swelling, and increased mucus production.

Anaphylaxis

A severe, potentially life-threatening allergic reaction that affects multiple body systems and requires immediate emergency treatment.

The Science

How Allergic Reactions Happen

Understanding the immune response helps explain why allergies develop and how they cause symptoms.

First Exposure (Sensitization)

The immune system encounters an allergen for the first time. It mistakenly identifies the harmless substance as a threat and creates specific antibodies (IgE) against it.

Antibody Attachment

These IgE antibodies attach to mast cells (immune cells found in skin, lungs, and digestive tract) and basophils in the blood, preparing the body for future encounters.

Re-exposure & Reaction

When exposed to the allergen again, it binds to the IgE antibodies on mast cells. This triggers the release of chemicals like histamine, causing allergic symptoms.

Important Note

Not everyone who is exposed to an allergen will become sensitized. And not everyone who becomes sensitized will develop clinical allergy symptoms. The development of allergies involves complex interactions between genetics and environment.

Risk Factors

Who Develops Allergies?

While anyone can develop allergies, certain factors can increase your likelihood.

Family History

If parents or siblings have allergies, asthma, or eczema, you're more likely to develop allergies. The tendency to develop allergies (atopy) is hereditary.

Age

Children are more likely to develop allergies than adults. Some allergies, like milk and egg allergies, may be outgrown, while others like peanut and tree nut allergies often persist.

Existing Conditions

Having asthma or one type of allergy increases your risk of developing other allergies. Conditions like eczema (atopic dermatitis) are also linked to allergy development.

Environmental Factors

Early childhood exposure (or lack thereof) to certain substances, pollution levels, and the timing of introduction to potential allergens can influence allergy development.

Common Triggers