Allergies are common, affecting more than 1 in 4 people at some point in their lives. An allergic reaction is an abnormal immune response the body launches when it is exposed to one or more substances that are otherwise harmless. These substances are called allergens. Most people develop mild to moderate allergies in childhood, though for some people they are quite severe.

Grass and Tree Pollen

An allergy to grass and tree pollen, called hay fever or allergic rhinitis, is extremely common. In 2016 alone, 20 million adults in the U.S. and 6.1 million children were diagnosed with hay fever. Symptoms often begin or increase at certain times of the year and can include

• sneezing
• runny nose or nasal congestion
• red, itchy, watery eyes (allergic conjunctivitis)
• itchiness in the nose, throat, or roof of the mouth
• postnasal drip
• cough
• fatigue

Dust Mites

Dust mites are microscopic insects that live in house dusti and feed on the dead skin cells humans regularly shed. They are attracted to humid environments and are commonly found in carpeting, bedding, and upholstered furniture. Dust mite allergies affect roughly 20 million Americans and produce symptoms similar to those of hay fever, such as sneezing, runny or stuffy nose, and itchy eyes. Such symptoms are typically mild; however, long-term exposure could lead to sinus infections and asthma.

Animal Dander

Dander is the dead skin cells regularly shed by animals such as cats and dogs. This, not the fur itself, is the is the most common allergy trigger related to pets, although the root cause of a pet allergy is the proteins found within the animal’s skin, saliva, and urine.Symptoms are similar to dust mites and hay fever: sneezing, stuffy or runny nose, and eye irritation. Some people experience severe symptom presentation and signs of asthma, such as wheezing and difficulty breathing.

Foods

Food allergies affect both children and adults, with 8% of children and 5% of adults having one or more. The most common culprits are cow’s milk, chicken eggs, tree nuts, peanuts, shellfish, wheat, soy, and fish. Milk and egg allergies most commonly affect the very young; research shows 90% of children outgrow their dairy allergy by the age of 3 and 68% of children will outgrow their egg allergy by 16.The most common food triggers for adults are shellfish, tree nuts, peanuts, and fish.

Insect Stings and Bites

Stings or bites from insects such as bees, wasps, hornets, and fire ants can trigger an allergic reaction that may be dangerous for some. Severe reactions can occur with any allergen; however, in the case of stings and bites, there is an additional degree of concern: because being stung is less common than accidentally consuming peanuts, for instance, people with this allergy are often unaware of it until it happens.Symptoms of a mild reaction include localized pain, redness, swelling, itching, warmth, and pimple-like spots. A severe reaction, also known as anaphylaxis, can cause difficulty breathing, hives, dizziness, nausea, diarrhea, and swelling of the face, throat, mouth, or tongue.

Medications

An allergy to medications or a drug allergy occurs when the body mistakenly identifies a medication as a virus or bacteria and produces an immune response as a result. This can happen the first time the person takes a medication or after repeated exposure. The most common drug allergies are to antibiotics, ibuprofen, aspirin, insulin, anti-seizure medications, and intravenous muscle relaxers.

Latex

A latex allergy is a reaction to proteins in rubber latex. Latex is used in many everyday products, such as balloons, rubber bands, household gloves, condoms, and bandages.A mild reaction may cause itchiness, redness, and hives. When the reaction is more severe, the person may develop sneezing, coughing, runny nose, itchy throat, watery eyes, difficulty breathing, and wheezing.

Mold

A mold allergy is a reaction to mold spores, which are tiny and lightweight enough to be carried through the air. A mild allergic reaction to mold is similar to other mild reactions: sneezing, coughing, watery eyes, postnasal drip, and itchy eyes, nose, and throat. It can also cause dry or scaly skin. A more severe reaction may include difficulty breathing, chest tightness, and wheezing.

Household Chemicals

Household chemicals are typically harmless in small amounts but can be toxic at higher exposures.The following substances are the most common allergy triggers:

• ammonia, found in numerous cleaning products such as glass cleaners
• hydrochloric acid, a common ingredient in toilet cleaners and disinfectants
• BPA, found in canned goods and plastic bottles; can leach into consumables.

Cosmetics and Personal Care Products

A number of ingredients in cosmetics and personal care items can trigger allergic reactions, including natural rubber, fragrances, preservatives, dyes, and metals such as nickel and gold. Fragrances, preservatives, and dyes are particularly widespread and are frequently found in soaps, lotions, deodorants, and detergents. Someone allergic to a specific compound may have to avoid various products.