People are allergic to a surprisingly wide range of substances, from foods and pollen to metals, medications, and insect venom. In 2024, nearly one in three U.S. adults (31.7%) had at least one diagnosed allergic condition, whether seasonal, food-related, or skin-based. Here’s a breakdown of the most common triggers and what makes each category distinct.
Seasonal and Environmental Allergens
Seasonal allergies are the single most common type, affecting about 25.2% of U.S. adults. The triggers are airborne particles that your immune system mistakenly treats as threats.
Pollen is the biggest culprit. Trees release pollen in spring, grasses in late spring and summer, and weeds (especially ragweed) in fall. These microspores travel as a fine dust that’s nearly impossible to avoid outdoors. Mold is another major trigger, thriving both indoors and out, particularly in damp areas like bathrooms, basements, and piles of fallen leaves.
Indoor allergens cause year-round symptoms for many people. Dust mites, microscopic creatures that feed on dead skin cells, live in bedding, upholstered furniture, and carpeting. Pet dander is equally pervasive. Up to 25% of children and adults show immune sensitivity to cat or dog allergens, though not all of them develop noticeable symptoms. The allergenic proteins come primarily from an animal’s skin cells and saliva, not the fur itself, which is why “hypoallergenic” breeds still cause reactions in many people.
The Nine Major Food Allergens
About 6.7% of U.S. adults have a diagnosed food allergy. Nine foods account for the vast majority of reactions, and U.S. law requires all of them to be clearly labeled on packaged foods:
- Milk
- Eggs
- Peanuts
- Tree nuts (almonds, walnuts, pecans, and others)
- Fish (bass, flounder, cod, and others)
- Crustacean shellfish (shrimp, crab, lobster)
- Wheat
- Soybeans
- Sesame (added to the list in 2021)
Milk and egg allergies are most common in young children and are frequently outgrown. Peanut, tree nut, fish, and shellfish allergies tend to be lifelong. Sesame was recognized as the ninth major allergen under the FASTER Act after evidence showed it caused severe reactions more often than previously appreciated. If you have a food allergy, the proteins in these foods trigger your immune system even in tiny amounts, which is why trace contamination during manufacturing matters.
Insect Stings and Venom
Stinging insects are one of the top triggers for severe allergic reactions. The species most likely to cause problems vary by region. Yellow jackets are the leading cause of venom allergy across the Northern Hemisphere. Paper wasps are particularly significant in the United States and Mediterranean Europe. Hornet sting allergies appear to be increasing, partly because invasive species like the Asian hornet are spreading into new territories.
Most people experience localized pain and swelling from a sting. A true venom allergy causes a systemic reaction: hives far from the sting site, swelling of the face or throat, difficulty breathing, or a drop in blood pressure. People who’ve had a systemic reaction to one sting carry a meaningful risk of a worse reaction next time, which is why many carry injectable epinephrine.
Medication Allergies
Penicillin is the most commonly reported drug allergy in the United States. Roughly 10% of patients have “penicillin allergy” noted in their medical records. The real number, though, is dramatically lower: fewer than 1% of those patients are truly allergic when formally tested. Many people were labeled allergic as children after a rash that was actually caused by the illness itself, not the drug. Because penicillin-type antibiotics are often the most effective and affordable option for common infections, a false allergy label can lead to the use of broader, less targeted alternatives.
Beyond penicillin, other medications that commonly trigger allergic reactions include aspirin, other over-the-counter pain relievers, and the contrast dyes used in certain imaging scans like CT scans. Drug allergies can range from a mild rash to full anaphylaxis, so any new medication that causes hives, facial swelling, or breathing difficulty warrants immediate attention.
Skin Contact Allergens
Eczema affects about 7.7% of U.S. adults, but contact allergies are a separate and overlapping problem. Contact dermatitis happens when your skin reacts to a substance it touches directly, producing an itchy, red, sometimes blistering rash.
Nickel is the most common contact allergen worldwide. It’s found in jewelry (especially piercing posts), belt buckles, zippers, bra hooks, eyeglass frames, coins, keys, and electronic devices like phones and laptops. People with a nickel allergy typically develop a rash within 12 to 48 hours of skin contact with the metal. Fragrances and preservatives in cosmetics, soaps, and lotions are the other leading contact allergens. Because these ingredients appear in hundreds of everyday products, identifying the exact trigger often requires patch testing by a dermatologist.
Latex
Latex allergy affects less than 1% of the general population, but the rate climbs to about 12% among healthcare workers who wear latex gloves regularly. Repeated exposure increases the risk of developing sensitivity over time.
What surprises many people is how many non-medical products contain latex: elastic waistbands, sneakers, swimsuits, baby bottle nipples, pacifiers, rubber bands, erasers, condoms, balloons, and bath mats. For someone with a latex allergy, even brief contact with these items can cause hives or, in severe cases, breathing difficulties. Synthetic alternatives (nitrile gloves, latex-free condoms) are widely available.
Alpha-Gal Syndrome: A Tick-Triggered Meat Allergy
One of the more unusual allergies to gain attention in recent years is alpha-gal syndrome, a red meat allergy caused by tick bites. When a lone star tick bites you, it can transfer a sugar molecule called alpha-gal from its saliva into your bloodstream. Your immune system may then flag that molecule as dangerous. Because alpha-gal is naturally found in the bodies of most mammals (but not humans), eating beef, pork, or lamb after being sensitized can trigger an allergic reaction.
What makes alpha-gal syndrome tricky is its timing. Reactions typically occur three to six hours after eating red meat, much later than typical food allergies, which makes it harder to connect symptoms to the cause. Most reported cases in the U.S. cluster in the South, East, and Central states, where lone star ticks are most common.
Anaphylaxis: When Allergies Turn Dangerous
Any allergy has the potential to cause anaphylaxis, a rapid, whole-body reaction that can stop breathing or collapse blood pressure. The most common triggers are foods (especially peanuts, tree nuts, shellfish, and milk in children), insect stings, medications, and latex. In rare cases, even exercise can trigger it.
Anaphylaxis is fatal if untreated. It develops within minutes of exposure and requires immediate treatment with epinephrine. People with known severe allergies typically carry an auto-injector for this reason. A first episode of anaphylaxis, though, often comes as a complete surprise, which is why any allergic reaction involving throat tightness, difficulty breathing, dizziness, or a rapid pulse is treated as an emergency.