Allergies

Overview

Allergies are a common condition affecting millions of individuals worldwide. They are the result of the immune system's hypersensitivity to typically harmless substances in the environment, known as allergens. These allergens can include substances such as pollen, dust mites, mold spores, pet dander, food, insect stings, and medicines. When a person with an allergy comes into contact with an allergen, their immune system reacts, leading to an allergic reaction.

A microscopic view of common allergens such as pollen, dust mites, and mold spores.

Types of Allergies

Allergies can be categorized into several types, depending on the allergen involved. Some of the most common types of allergies include:

Food Allergies: These are caused by an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives, or swollen airways.
Drug Allergies: These are a group of symptoms caused by an allergic reaction to a drug. Common drug allergies include reactions to penicillin and related antibiotics.
Insect Sting Allergies: These occur when the immune system overreacts to the venom of stinging insects such as bees, wasps, hornets, yellow jackets, and fire ants.
Pet Allergies: These are triggered by exposure to pets, most commonly cats and dogs, and are caused by sensitivity to proteins found in the animals' skin cells, urine, or saliva.
Hay Fever (also known as allergic rhinitis): This is an allergic response to allergens such as dust mites, pet dander, or molds. Seasonal hay fever is typically caused by an allergy to pollen from trees, grasses, or weeds.

Symptoms

The symptoms of allergies can vary depending on the type of allergy and the severity of the reaction. Common symptoms include:

Sneezing
Itching of the nose, eyes, or roof of the mouth
Runny, stuffy nose
Watery, red, or swollen eyes (conjunctivitis)
Swelling of the lips, tongue, face, or throat
Hives
Anaphylaxis (a severe, potentially life-threatening allergic reaction)

In some cases, allergies can trigger a severe reaction known as anaphylaxis. This is a medical emergency that requires immediate treatment.

Causes

Allergies occur when the immune system mistakenly identifies a harmless substance as a threat and produces antibodies to fight it. These antibodies release chemicals, such as histamine, that cause allergy symptoms. The exact cause of why the immune system reacts this way is still not fully understood, but it is believed to be a combination of genetic and environmental factors.

Diagnosis

The diagnosis of allergies typically involves a combination of a medical history, physical examination, and tests. Skin tests and blood tests are the most common methods used to diagnose allergies. In a skin test, a small amount of a suspected allergen is applied to the skin using a tiny needle that barely penetrates the skin's surface. A blood test, on the other hand, measures the amount of specific antibodies produced in response to an allergen.

Treatment

While there is no cure for allergies, they can be managed with prevention and treatment. Avoidance of known allergens is the best way to prevent allergic reactions. Medications can help to reduce symptoms, and include antihistamines, corticosteroids, and decongestants. In some cases, immunotherapy (allergy shots or under-the-tongue tablets) may be recommended. In the case of severe reactions, an emergency injection of epinephrine can be life-saving.

Prevention

Preventing allergic reactions depends largely on the type of allergy a person has. General measures can include avoiding known allergens, using "mite-proof" bedding, maintaining a clean home, and wearing a medical alert bracelet or necklace that lets others know of a severe allergy (particularly important for food and drug allergies).