The most common allergies fall into a few broad categories: pollen, food, medications, insect venom, and substances you touch or breathe indoors. Roughly 40% of the world’s population has immune sensitivity to at least one environmental protein, making allergies one of the most widespread chronic conditions on the planet. Here are the 10 most common, along with what makes each one distinct.
1. Pollen (Seasonal Allergies)
Pollen allergy, often called hay fever or allergic rhinitis, tops the list. It affects between 10% and 30% of people worldwide, and CDC data from 2024 shows that about 25% of American adults and 21% of children deal with seasonal allergies. The culprits are airborne pollen grains from trees (spring), grasses (late spring and summer), and ragweed or other weeds (fall). Your immune system treats these particles as threats, triggering sneezing, nasal congestion, itchy eyes, and fatigue. Symptoms tend to follow a predictable calendar depending on where you live, which helps distinguish pollen allergy from a cold.
2. Dust Mites
Dust mites are microscopic creatures that thrive in bedding, upholstered furniture, and carpeting. They’re one of the most potent indoor allergy triggers, and exposure is nearly universal in homes with any amount of soft furnishing. Research on children with asthma found that even low levels of dust mite allergen in household dust significantly raised the odds of developing sensitivity, while high exposure levels increased the risk ninefold compared to unexposed children. Cities with warm, humid climates tend to have the worst dust mite levels. San Diego, for example, had moderate-to-high dust mite concentrations in nearly 79% of homes studied.
Unlike pollen allergies, dust mite symptoms are year-round: a stuffy nose in the morning, sneezing when you make the bed, or worsening asthma at night. Encasing pillows and mattresses in allergen-proof covers and washing bedding in hot water weekly are the most effective ways to reduce exposure.
3. Shellfish
Shellfish allergy is the most common food allergy in the United States, affecting an estimated 8.4 million Americans. Shrimp, crab, and lobster are the usual triggers, though clams, mussels, and oysters can also cause reactions. Unlike many childhood food allergies, shellfish allergy typically develops in adulthood and is lifelong. Reactions range from hives and digestive upset to full anaphylaxis, making it one of the food allergies most likely to send someone to the emergency room.
4. Milk
Cow’s milk allergy affects roughly 6.2 million Americans and is one of the earliest allergies to appear, often showing up in the first year of life. It’s different from lactose intolerance, which is a digestive issue. A true milk allergy involves the immune system reacting to proteins in milk, causing symptoms like hives, vomiting, wheezing, or in severe cases, anaphylaxis. The good news: most children with milk allergy outgrow it by age 5 or 6, though a small percentage carry it into adulthood.
5. Peanuts
Peanut allergy also affects about 6.2 million Americans and is the most prevalent food allergen in children specifically. It gets outsized attention for good reason: peanut reactions tend to be more severe than many other food allergies, and only about 20% of allergic children eventually outgrow it. Even trace amounts can trigger symptoms in highly sensitive individuals, which is why peanut-free policies are common in schools. Early introduction of peanut-containing foods to infants (around 4 to 6 months, with pediatric guidance) has been shown to dramatically reduce the risk of developing this allergy.
6. Pet Dander
Cat and dog allergies are triggered not by fur itself but by proteins found in the animal’s skin flakes, saliva, and urine. Cat allergens are especially sticky and lightweight, staying airborne for hours and clinging to clothing, which is why you can have a reaction in a home where a cat lived months ago. Symptoms overlap heavily with dust mite and pollen allergies: sneezing, congestion, itchy eyes, and in some people, asthma flare-ups. Because pet dander is so pervasive in public spaces (carried on clothing), even people who don’t own pets can experience symptoms in offices, schools, and public transit.
7. Insect Stings
Bee, wasp, yellow jacket, and hornet stings cause localized pain and swelling in most people, but about 3% of adults and nearly 1% of children develop a serious systemic allergic reaction to insect venom. These reactions can escalate to anaphylaxis, with symptoms like throat swelling, a drop in blood pressure, and difficulty breathing. Insect venom allergy is one of the leading causes of anaphylaxis-related emergency visits. If you’ve had a reaction that extended beyond the sting site (widespread hives, dizziness, breathing trouble), allergy testing and carrying an epinephrine auto-injector are standard next steps.
8. Mold
Mold spores float through indoor and outdoor air, making mold allergy both seasonal and year-round depending on where you live. Outdoor mold peaks in late summer and fall as leaves decompose, while indoor mold thrives in damp areas like bathrooms, basements, and around leaky pipes. Symptoms mirror other airborne allergies, but mold exposure is also closely linked to worsening asthma. Controlling indoor humidity below 50% and fixing water leaks promptly are the most practical steps for reducing exposure.
9. Medications
Drug allergies may affect up to 10% of the global population, and penicillin is by far the most commonly reported trigger. About 10% of U.S. patients have a penicillin allergy noted in their medical records. Here’s the catch: fewer than 1% of those patients are actually allergic when formally tested. Most people labeled as penicillin-allergic had a childhood reaction (often a rash during an infection) that was never truly an allergy, or they’ve lost their sensitivity over time. This matters because a penicillin allergy label steers doctors toward broader, more expensive antibiotics that can carry more side effects and contribute to antibiotic resistance. If you’ve been told you’re allergic to penicillin, allergy testing can clarify whether the label still applies.
Medications are also the most common trigger in fatal anaphylaxis cases. Antibiotics account for the majority of anaphylactic deaths in retrospective studies, making it important to distinguish a true drug allergy from a side effect or coincidental rash.
10. Nickel and Other Contact Allergens
Nickel is the most common cause of allergic contact dermatitis, a delayed skin reaction that produces an itchy, red, sometimes blistering rash wherever the metal touches your skin. It’s found in jewelry (especially earrings and belt buckles), watchbands, zippers, eyeglass frames, and even some phones and laptops. The allergy develops over time with repeated exposure, which is why many people first notice it after getting their ears pierced. Once you’re sensitized, the allergy is permanent, though avoiding direct skin contact with nickel-containing items prevents flare-ups entirely. Fragrance chemicals in perfumes, lotions, and household products are the other major category of contact allergens.
Why Some Allergies Overlap
If you’re allergic to one thing on this list, you’re statistically more likely to be allergic to others. This tendency, called atopy, means your immune system is generally more reactive to harmless substances. A child with eczema, for instance, has a higher chance of later developing food allergies, then hay fever, then asthma, a progression sometimes called the allergic march. Among the nine major food allergens recognized in the U.S. (milk, egg, peanut, tree nuts, wheat, soy, fish, shellfish, and sesame), together they account for at least 90% of serious food allergy reactions.
Tree nut allergy affects roughly 3.9 million Americans, egg allergy about 2.7 million, and wheat allergy about 2.4 million. Sesame, the newest addition to the major allergen list (added in 2021), affects an estimated 700,000 people. These didn’t make the top 10 list by overall prevalence, but they’re significant enough that U.S. food labeling laws require them to be clearly identified on packaging.