Allergy symptoms range from a runny nose and itchy eyes to hives, stomach pain, and in severe cases, life-threatening breathing difficulties. Nearly one in three U.S. adults has at least one diagnosed allergic condition, making allergies one of the most common chronic health issues in the country. The specific symptoms you experience depend on what you’re allergic to and how your body encounters it, whether through breathing, eating, touching, or being stung.
Why Allergies Cause Symptoms
An allergic reaction starts when your immune system misidentifies a harmless substance, like pollen or a food protein, as a threat. The first time you’re exposed, your body produces antibodies designed to recognize that specific substance. The next time it shows up, those antibodies signal immune cells called mast cells to release histamine and other inflammatory chemicals into your tissues.
Histamine is the main driver behind most allergy symptoms. It causes smooth muscles in your airways to tighten, makes blood vessels leak fluid into surrounding tissue (producing swelling and congestion), and triggers nerve endings that create itching. It also shifts your immune system’s activity toward producing even more of the inflammatory signals that keep the reaction going. This is why allergies tend to get worse with repeated exposure rather than better, and why antihistamines work by blocking histamine’s effects at the cellular level.
Respiratory and Nasal Symptoms
Seasonal allergies (hay fever) are the most common type, affecting about 25% of American adults. When you inhale allergens like pollen, dust mites, mold spores, or pet dander, your body mounts an immune response in your nasal passages and airways. The hallmark symptoms include:
- Nasal congestion and a runny nose with clear, watery mucus
- Sneezing, often in rapid bursts
- Itchy nose, throat, and roof of the mouth
- Red, watery, itchy eyes
- Postnasal drip, which can cause a sore throat and cough
- Sinus pressure and headaches
- Dark circles under the eyes, sometimes called “allergic shiners”
- Fatigue
In people with allergic asthma, inhaled allergens can also trigger wheezing, chest tightness, and difficulty breathing. These symptoms overlap with non-allergic asthma but tend to flare predictably during high-pollen seasons or after contact with a known trigger like cats or dust.
Skin Reactions
Allergies can produce several distinct skin reactions, each with its own pattern. Hives (urticaria) are raised, red, itchy welts that can appear anywhere on your body and range from small dots to large patches. They often appear suddenly and may shift location over hours. Angioedema is related but affects deeper layers of skin, causing swelling that typically shows up around the eyelids, lips, tongue, hands, or feet. Unlike hives, angioedema usually isn’t itchy or red.
Eczema (atopic dermatitis) produces a scaly, itchy rash that commonly appears on the face, inside the elbows, behind the knees, and on the wrists and ankles. It tends to be a chronic, recurring condition rather than a sudden reaction to a single exposure. About 7.7% of U.S. adults have diagnosed eczema.
Contact dermatitis occurs when your skin directly touches an allergen, with poison ivy being the classic example. The reaction typically produces an itchy, red, blistered rash at the site of contact. It usually takes 12 to 72 hours to develop after exposure, which can make it tricky to identify the cause. Irritant contact dermatitis, by contrast, tends to burn or sting more than it itches.
Food Allergy Symptoms
Roughly 6.7% of adults have a diagnosed food allergy. Symptoms typically appear within minutes to two hours after eating the trigger food and can affect multiple body systems at once. The most common signs include tingling or itching in the mouth, swelling of the lips, face, tongue, or throat, hives, stomach pain, nausea, vomiting, and diarrhea. Some people also experience nasal congestion, wheezing, or dizziness.
A related condition called pollen-food allergy syndrome (or oral allergy syndrome) affects many people who already have hay fever. Certain raw fruits, vegetables, nuts, and spices contain proteins that resemble pollen, and your immune system can react to them. This usually causes tingling or itching confined to the mouth, though in more serious cases it can cause throat swelling. Cooking the food typically breaks down the proteins enough to prevent the reaction.
It’s worth noting that food intolerances can mimic food allergy symptoms, particularly nausea, cramping, and diarrhea. The key difference is that a true food allergy involves the immune system and can escalate to a dangerous reaction, while an intolerance (like lactose intolerance) generally causes only digestive discomfort.
Insect Sting and Drug Allergy Symptoms
Insect stings from bees, wasps, hornets, and fire ants cause localized pain, redness, and swelling in most people, but an allergic reaction goes further. A large local reaction produces swelling that extends well beyond the sting site and may worsen over a day or two. A systemic reaction can cause hives across your body, facial or throat swelling, breathing difficulty, a rapid pulse, nausea, and dizziness, all of which can signal the start of anaphylaxis.
Drug allergies most commonly cause skin symptoms: a widespread rash, hives, or itching. Some drug reactions also produce facial swelling, wheezing, or fever. Symptoms can appear within an hour of taking the medication or, in some cases, days later, which makes drug allergies particularly difficult to pin down.
Signs of Anaphylaxis
Anaphylaxis is the most dangerous form of allergic reaction. It can be triggered by foods, insect stings, medications, or latex, and it typically begins within minutes of exposure, though it can sometimes be delayed by 30 minutes or more. During anaphylaxis, the immune system releases a massive wave of chemicals that can send your body into shock.
The warning signs include a rapid or weak pulse, sudden drop in blood pressure, swelling of the tongue or throat, severe difficulty breathing, widespread hives, flushed or pale skin, nausea, vomiting, diarrhea, dizziness, and fainting. Even one or two of these symptoms after a known allergen exposure warrants emergency treatment. Anaphylaxis can stop breathing or heartbeat and is always a medical emergency.
Allergies vs. a Cold
Because allergies and colds share symptoms like congestion, sneezing, and a runny nose, it’s easy to confuse them. A few differences help you tell them apart. Allergies almost never cause a fever, while colds often do. The mucus from allergies is typically thin and clear, while cold mucus often thickens and turns yellow or green as the infection progresses. Colds generally resolve in 3 to 10 days. Allergy symptoms can persist for weeks or as long as you’re exposed to the trigger. Itchy eyes, nose, and throat strongly point toward allergies, as itching is uncommon with viral infections.
How Allergies Are Diagnosed
If your symptoms are persistent or you can’t identify the trigger, allergy testing can help narrow it down. The most common method is a skin prick test, where tiny amounts of up to 50 suspected allergens are applied to your skin through small scratches, usually on your forearm or back. If you’re allergic, a raised, itchy bump resembling a mosquito bite develops within about 15 minutes. Larger bumps generally indicate greater sensitivity.
When skin testing isn’t an option, such as for people taking certain medications or those with severe skin conditions, a blood test can measure the levels of allergy-specific antibodies in your system. For suspected food allergies, your provider may also recommend an elimination diet or a supervised oral food challenge to confirm which foods cause reactions.