The most common allergens fall into a handful of categories: foods, airborne particles like pollen and dust mites, insect stings, certain medications, metals, and latex. About 10.8% of U.S. adults and 7.6% of children have at least one confirmed food allergy, and millions more react to environmental triggers they breathe in every day. Here’s what you’re most likely to encounter in each category.
The Nine Major Food Allergens
U.S. federal law recognizes nine foods as major allergens, and manufacturers are required to clearly label them on packaging. These nine account for the vast majority of serious food-related allergic reactions:
- Milk
- Eggs
- Peanuts
- Tree nuts (almonds, walnuts, pecans, and others)
- Fish (bass, flounder, cod, and others)
- Crustacean shellfish (crab, lobster, shrimp)
- Wheat
- Soybeans
- Sesame
Sesame was added to this list in 2023 under the FASTER Act after growing evidence that it caused significant allergic reactions. Among children, peanut allergy is the most common at 2.2%, followed by milk (1.9%) and shellfish (1.3%). The pattern shifts in adults: shellfish tops the list at 2.9%, followed by milk and peanuts tied at about 1.8% each. Nearly half of adults with shellfish or wheat allergies developed them in adulthood rather than childhood, so food allergies aren’t just something you’re born with.
Pollen: Trees, Grasses, and Weeds
Pollen is probably the allergen most people think of first. It triggers seasonal symptoms like sneezing, itchy eyes, and congestion, commonly called hay fever. The timing of your symptoms often reveals the culprit. Tree pollen dominates in spring, grass pollen peaks in late spring and summer, and weed pollen takes over in late summer and fall.
Ragweed is one of the most potent weed allergens in North America, with a single plant capable of releasing billions of pollen grains. Mugwort and wall pellitory are other significant weed triggers, especially in parts of Europe. Because pollen counts fluctuate with weather, wind, and geography, your symptoms can vary dramatically from one year to the next or even one neighborhood to the next.
Dust Mites and Pet Dander
Dust mites are microscopic creatures that live in bedding, upholstered furniture, and carpeting. The allergic reaction isn’t to the mites themselves but to proteins in their droppings. One protein in particular, a digestive enzyme found in mite fecal matter, is responsible for triggering an immune response in 80 to 90 percent of people with dust mite allergy. The mites’ shed exoskeletons can also cause reactions. A separate protein has been linked specifically to eczema flare-ups in sensitized people.
Pet allergies work similarly. The trigger isn’t fur itself but proteins found in an animal’s dander (tiny flakes of skin), saliva, and urine. These particles are small and sticky, so they cling to clothing, furniture, and walls long after an animal has left the room. Cat allergens tend to be especially persistent indoors. Even homes without pets can harbor enough transferred dander to cause symptoms in highly sensitive people.
Mold
Mold releases tiny spores into the air, and those spores act as allergens when inhaled. Four mold types cause the most allergic reactions: Alternaria, Cladosporium, Penicillium, and Aspergillus. The first two are primarily outdoor molds that peak in warm, humid months. Penicillium and Aspergillus thrive indoors, growing in damp areas like bathrooms, basements, and around leaky pipes. Between 5 and 20 percent of people seen at allergy clinics show sensitivity to mold, depending on the local climate. Mold allergy symptoms often overlap with pollen season, making it easy to mistake one for the other.
Insect Stings
Bee stings and wasp stings are the most common causes of insect venom allergy. Most people experience localized pain and swelling after a sting, which is normal. An allergic reaction goes further: hives spreading away from the sting site, swelling of the face or throat, difficulty breathing, dizziness, or a drop in blood pressure. These symptoms can escalate to anaphylaxis, a severe whole-body reaction. People who have had a systemic reaction to one sting are at higher risk of a similar or worse reaction if stung again.
Medications
Penicillin is the most commonly reported drug allergy. About 10% of U.S. patients have a penicillin allergy noted in their medical records. The actual number is far smaller: when those patients are formally evaluated, fewer than 1% turn out to be truly allergic. Many people were labeled allergic as children after a rash that may have been caused by the underlying infection rather than the drug. This matters because a penicillin allergy label often pushes doctors toward broader, more expensive antibiotics that can carry their own risks. If you’ve been told you’re allergic to penicillin, allergy testing can clarify whether the label still applies.
Nickel and Other Contact Allergens
Nickel is the single most common cause of allergic contact dermatitis, the itchy, red rash that develops where your skin touches something it reacts to. Nickel is everywhere: jewelry, belt buckles, eyeglass frames, zippers, kitchen utensils, and even some phone cases. The reaction typically appears 12 to 48 hours after contact, which makes it harder to identify than an immediate allergy. Fragrances and preservatives in cosmetics, hair dyes, soaps, and lotions are other frequent contact triggers. If you notice a recurring rash in the same spot, the culprit is often something you wear or apply to that area regularly.
Latex
Natural rubber latex, found in gloves, balloons, elastic waistbands, condoms, rubber bands, and many medical devices, can cause reactions ranging from skin irritation to anaphylaxis. Healthcare workers and people who have had multiple surgeries face higher risk because of repeated exposure. Latex proteins can also cross-react with certain foods, particularly bananas, avocados, chestnuts, and kiwi. If you react to latex, you may notice tingling or itching after eating these foods.
How an Allergic Reaction Happens
Regardless of the trigger, most allergic reactions follow the same basic sequence. On your first exposure to an allergen, your immune system mistakenly identifies it as a threat and produces antibodies designed to recognize it. These antibodies attach to mast cells, which are immune cells stationed in your skin, airways, and gut. Nothing happens yet.
On a second or subsequent exposure, the allergen binds to those waiting antibodies, which signals the mast cells to dump their contents. Within minutes, the cells release histamine and other inflammatory chemicals. Histamine is what causes the familiar symptoms: swelling, itching, mucus production, and in the airways, tightening of the muscles around your breathing passages. This is why antihistamines work for mild reactions. In severe cases, the cascade happens throughout the body simultaneously, causing anaphylaxis.
The speed and severity of this process vary widely. A pollen allergy might give you a runny nose. The same immune mechanism triggered by a peanut or bee sting can be life-threatening. The difference comes down to how much allergen enters your body, how it enters (skin, lungs, or bloodstream), and how strongly your immune system has been primed to respond.