What Are Allergies? Types, Symptoms, and Treatment

What Are Allergies and How Do They Develop?

Allergies occur when your immune system mistakenly identifies a harmless substance — like pollen, pet dander, or peanut protein — as dangerous and launches a defensive attack. This overreaction triggers the release of histamine and other chemicals, causing symptoms like sneezing, itching, swelling, and in severe cases, anaphylaxis.

Your immune system normally protects you from genuinely harmful invaders like bacteria and viruses. In people with allergies, the immune system produces immunoglobulin E (IgE) antibodies against substances that are typically harmless. When you encounter the allergen again, these IgE antibodies recognize it and signal mast cells to release histamine and other inflammatory mediators. This cascade of chemical signals produces the familiar symptoms of an allergic reaction.

Allergies develop through a process called sensitization. During your first exposure to an allergen, your immune system may quietly begin producing IgE antibodies without causing any symptoms. Subsequent exposures trigger progressively stronger immune responses, eventually producing noticeable symptoms. This is why someone can eat a food for years before suddenly developing an allergy to it.

The World Health Organization estimates that allergic diseases affect 30 to 40 percent of the global population, making them one of the most common chronic conditions worldwide [2]. Allergy prevalence has been increasing steadily over the past several decades, particularly in industrialized countries. The hygiene hypothesis suggests that reduced exposure to infections in early childhood may contribute to immune systems that overreact to harmless substances.

The WHO estimates allergic diseases affect 30 to 40 percent of the global population [2]

What Should You Do if You Think You Have Allergies?

Start by tracking your symptoms and potential triggers in a daily journal — note when symptoms occur, where you are, and what you were exposed to. Over-the-counter antihistamines like cetirizine (Zyrtec) or loratadine (Claritin) can provide initial relief while you schedule an appointment with an allergist for proper testing.

The first step in managing allergies is identifying what triggers your symptoms. Keep a detailed log of when symptoms occur, what you were doing, and your environment. Note whether symptoms happen indoors or outdoors, during specific seasons, or after eating certain foods. This information is invaluable when you see a healthcare provider, as it helps narrow down the potential allergens.

While waiting for a medical evaluation, several over-the-counter options can help. Second-generation antihistamines like cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra) effectively reduce sneezing, itching, and runny nose without significant drowsiness. Nasal saline rinses can flush allergens from nasal passages. For nasal congestion, intranasal corticosteroid sprays like fluticasone (Flonase) are considered the most effective first-line treatment (Source: AAAAI Clinical Practice Guidelines) [1].

The American College of Allergy, Asthma, and Immunology recommends seeing a doctor if over-the-counter medications do not control your symptoms within two weeks, if symptoms interfere with sleep or daily activities, or if you experience any wheezing or shortness of breath. Do not wait if you have ever had a severe allergic reaction — seek an allergist evaluation as soon as possible.

According to the AAAAI, intranasal corticosteroids are the single most effective medication class for allergic rhinitis [1]

What Are the Most Common Types of Allergies?

The most common allergy types are seasonal allergic rhinitis (hay fever), perennial allergic rhinitis from indoor allergens, food allergies, drug allergies, insect sting allergies, and contact dermatitis. Each type involves different allergens, produces distinct symptoms, and may require different management strategies.

Seasonal allergic rhinitis, commonly called hay fever, affects approximately 81 million Americans annually according to the Asthma and Allergy Foundation of America [3]. Tree pollen peaks in spring, grass pollen in late spring and summer, and ragweed pollen in fall. Symptoms include sneezing, runny nose, nasal congestion, and itchy, watery eyes. If you notice your symptoms follow a predictable seasonal pattern, hay fever is likely the cause.

Perennial allergic rhinitis persists year-round and is typically caused by dust mites, mold spores, cockroach droppings, or pet dander. These indoor allergens can be particularly difficult to avoid since they accumulate in homes and workplaces. You may notice symptoms worsen in enclosed spaces or during certain activities like vacuuming or making the bed.

Food allergies affect approximately 32 million Americans, including 5.6 million children under age 18 [10]. The nine major food allergens — milk, eggs, peanuts, tree nuts, wheat, soy, fish, shellfish, and sesame — account for about 90 percent of reactions. Food allergies can range from mild oral itching to severe anaphylaxis. Drug allergies most commonly involve penicillin and related antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, and sulfonamide antibiotics.

Insect sting allergies affect approximately 5 percent of the population and can cause severe systemic reactions. Bees, wasps, hornets, yellow jackets, and fire ants are the most common triggers. Contact dermatitis involves delayed skin reactions to substances like nickel (in jewelry), latex, poison ivy, fragrances, and preservatives in cosmetics.

The AAFA reports that seasonal allergic rhinitis affects approximately 81 million Americans each year [3]

• Seasonal allergic rhinitis (hay fever): triggered by pollen from trees, grasses, and weeds — affects 81 million Americans annually
• Perennial allergic rhinitis: caused by year-round indoor allergens including dust mites, mold, pet dander, and cockroaches
• Food allergies: nine major allergens (peanuts, tree nuts, milk, eggs, shellfish, wheat, soy, fish, sesame) cause 90% of reactions
• Drug allergies: most commonly penicillin, NSAIDs, sulfonamides, and chemotherapy agents — always inform your healthcare providers
• Insect sting allergies: bees, wasps, hornets, yellow jackets, and fire ants — can cause anaphylaxis in about 5% of people
• Contact dermatitis: delayed skin reactions to nickel, latex, poison ivy, fragrances, and cosmetic preservatives

What Are the Symptoms of Allergies?

Allergy symptoms vary depending on the allergen type and how you are exposed. Respiratory allergies typically cause sneezing, runny nose, congestion, and itchy eyes. Food allergies can cause hives, swelling, digestive upset, and potentially life-threatening anaphylaxis. Skin allergies produce redness, itching, and rashes at the point of contact.

Allergic rhinitis symptoms include sneezing, clear watery nasal discharge, nasal congestion, postnasal drip, itchy nose and throat, and watery itchy eyes. These symptoms can significantly impact quality of life, affecting sleep, concentration, work productivity, and school performance. Two classic physical signs that help distinguish allergies from a cold are the allergic salute — the upward rubbing of the nose with the palm — and allergic shiners — dark circles under the eyes caused by nasal congestion.

Food allergy symptoms typically appear within minutes to two hours after eating the offending food. Mild symptoms include tingling or itching in the mouth, hives or eczema flares, and abdominal pain or diarrhea. Severe food allergy reactions can progress rapidly to anaphylaxis, characterized by throat swelling, difficulty breathing, rapid pulse, dizziness, and a dangerous drop in blood pressure.

Skin allergy symptoms depend on the type of exposure. Contact dermatitis causes red, itchy, and sometimes blistering rashes at the site of contact, usually appearing 24 to 72 hours after exposure. Hives (urticaria) — raised, itchy welts that can appear anywhere on the body — may result from food allergies, drug allergies, or insect stings and typically develop within minutes. Eczema (atopic dermatitis) is a chronic skin condition closely linked to allergies that causes dry, itchy, inflamed patches of skin.

The AAAAI Anaphylaxis Practice Parameter recommends that all patients at risk of anaphylaxis carry two epinephrine auto-injectors at all times [9]

How Are Allergies Diagnosed?

Allergists diagnose allergies through a combination of detailed medical history, physical examination, and specific tests. Skin prick testing is the most common and reliable method, providing results within 15 to 20 minutes. Blood tests measuring allergen-specific IgE levels offer an alternative when skin testing is not appropriate.

Skin prick testing involves placing small drops of purified allergen extracts on your forearm or back and then lightly pricking the skin through each drop. A positive result appears as a raised, red, itchy bump called a wheal within 15 to 20 minutes. Skin prick tests can evaluate dozens of allergens simultaneously and have good sensitivity and specificity. The AAAAI considers skin prick testing the gold standard for diagnosing IgE-mediated allergies [1].

Blood tests, specifically serum-specific IgE tests (formerly called RAST tests), measure the amount of IgE antibodies your blood produces in response to specific allergens. These tests are useful when skin testing cannot be performed — for example, in patients taking antihistamines that cannot be stopped, those with severe eczema covering large skin areas, or patients at high risk of anaphylaxis from skin testing.

Component-resolved diagnostics (CRD), a newer approach, can identify which specific proteins within an allergen source you react to. This helps predict whether a reaction is likely to be mild or severe, and can distinguish true food allergies from cross-reactive sensitivities. For suspected food allergies, oral food challenges — eating small, increasing amounts of the suspect food under medical supervision — remain the definitive diagnostic test [8].

What Are the Best Treatment Options for Allergies?

Allergy treatment follows a stepwise approach: allergen avoidance first, then medications to control symptoms, and immunotherapy for long-term desensitization. Second-generation antihistamines and intranasal corticosteroids are the primary first-line medications. For lasting relief, allergen immunotherapy through shots or sublingual tablets can modify the underlying immune response.

Allergen avoidance is the foundation of allergy management, though it is not always practical. For dust mite allergies, encasing mattresses and pillows in allergen-proof covers, washing bedding weekly in hot water above 130°F, and maintaining indoor humidity below 50 percent can significantly reduce exposure. For pollen allergies, monitoring local pollen counts through the National Allergy Bureau, keeping windows closed during high-pollen days, showering after outdoor activities, and using HEPA air purifiers can help reduce symptoms.

When avoidance alone is insufficient, medications provide symptom relief. Second-generation antihistamines like cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra) are first-line treatments for mild to moderate allergic rhinitis. Common side effects are minimal but may include mild drowsiness with cetirizine. Intranasal corticosteroids such as fluticasone (Flonase), mometasone (Nasonex), and budesonide (Rhinocort) are the most effective single medication class for allergic rhinitis and work best when used consistently rather than as-needed.

Leukotriene receptor antagonists like montelukast (Singulair) can help patients who have both allergies and asthma. However, the FDA issued a boxed warning for montelukast in 2020 regarding potential neuropsychiatric side effects including mood changes and suicidal thoughts — discuss the risks and benefits with your doctor [11]. For eye symptoms, antihistamine eye drops like olopatadine (Patanol) or ketotifen (Zaditor) provide targeted relief.

Allergen immunotherapy gradually exposes your immune system to increasing doses of specific allergens over three to five years, retraining the immune response. Subcutaneous immunotherapy (allergy shots) has been used for over a century and is effective for environmental and venom allergies. Sublingual immunotherapy (SLIT) tablets, available for grass pollen, ragweed, and dust mites, offer a convenient at-home alternative. A systematic review in JAMA found that immunotherapy can reduce symptom severity by 30 to 40 percent compared to placebo [4].

A systematic review in JAMA found that allergen immunotherapy reduces allergy symptom severity by 30 to 40 percent compared to placebo [4]

What Are the Complications if Allergies Are Left Untreated?

Untreated allergies can lead to chronic sinusitis, ear infections, worsening asthma, sleep disruption, and reduced quality of life. Severe untreated food or venom allergies carry the risk of fatal anaphylaxis. Early diagnosis and treatment can prevent most of these complications.

Chronic nasal congestion from untreated allergic rhinitis can block the sinus drainage pathways, leading to recurrent or chronic sinusitis — a condition that affects more than 30 million Americans annually. Untreated nasal allergies also increase the risk of middle ear infections (otitis media), particularly in children, because congestion can block the Eustachian tubes that connect the nose to the middle ear.

Perhaps the most significant complication is the allergy-asthma connection. According to the AAFA, approximately 60 percent of people with asthma have allergic asthma, where allergen exposure triggers airway inflammation and bronchospasm [3]. Untreated allergies can worsen existing asthma or contribute to its development — a phenomenon called the allergic march, where eczema in infancy progresses to allergic rhinitis and then asthma.

Sleep disruption from nasal congestion is an underappreciated complication. Studies show that moderate to severe allergic rhinitis reduces sleep quality comparably to conditions like chronic pain, leading to daytime fatigue, impaired concentration, and reduced productivity [6]. Children with untreated allergies may experience learning difficulties and behavioral problems related to poor sleep and chronic nasal breathing obstruction.

• Chronic sinusitis: persistent sinus inflammation and infections from blocked drainage — affects 30+ million Americans
• Allergic asthma: allergen-triggered airway inflammation causing wheezing, coughing, and shortness of breath
• Ear infections: especially in children, from Eustachian tube congestion
• Sleep disruption: nasal congestion reduces sleep quality, causing daytime fatigue and impaired concentration
• Allergic march: progression from eczema to allergic rhinitis to asthma, particularly in children
• [Rare] Fatal anaphylaxis: untreated severe food or venom allergies without access to epinephrine carry a small but real risk of death

How Can You Live Well With Allergies?

Living well with allergies means combining consistent medical treatment with practical environmental controls, dietary awareness, and stress management. Most people with allergies can achieve excellent symptom control and maintain a full, active lifestyle with the right management plan.

Create an allergy-friendly home environment by focusing on your bedroom first — you spend about a third of your life there. Use allergen-proof mattress and pillow encasings, wash bedding weekly in hot water above 130°F, remove carpeting if possible, and keep humidity below 50 percent to discourage dust mites and mold. A HEPA air purifier in the bedroom can reduce airborne allergens significantly. Keep pets out of the bedroom, even if they are allowed in other areas of the home.

Diet can play a supporting role in managing allergies. Some research suggests that anti-inflammatory foods rich in omega-3 fatty acids (salmon, sardines, walnuts, flaxseed) and quercetin (onions, apples, berries) may help modulate immune responses, though evidence is limited. If you have food allergies, become an expert label reader — the Food Allergen Labeling and Consumer Protection Act (FALCPA) requires clear labeling of the nine major allergens on packaged foods. When eating out, communicate your allergies clearly and ask about ingredients and cross-contamination.

Stress can worsen allergy symptoms by increasing inflammatory cytokines and destabilizing mast cells. Regular exercise (at least 150 minutes per week of moderate activity), adequate sleep (7 to 9 hours), and stress-reduction techniques like deep breathing or meditation can help. Exercise outdoors when pollen counts are lower — typically late afternoon or after rain — or choose indoor activities during peak allergy season.

Connect with support resources if allergies significantly affect your quality of life. Organizations like the Asthma and Allergy Foundation of America (AAFA) and Food Allergy Research and Education (FARE) offer educational materials, support groups, and advocacy resources. If allergies are causing anxiety — particularly around food or anaphylaxis risk — talk to your doctor about whether counseling might help.

When Should You See a Doctor for Allergies?

See a doctor if over-the-counter medications do not adequately control your symptoms after two weeks, if allergies interfere with sleep or daily activities, if you develop signs of asthma like wheezing or chest tightness, or if you have ever experienced a severe allergic reaction requiring emergency care.

While mild allergies can often be managed with over-the-counter treatments, certain situations warrant professional evaluation. An allergist can perform comprehensive testing to identify your specific triggers, develop a personalized avoidance plan, and prescribe targeted therapies. Referral to an allergist is particularly important if you have multiple allergies, allergies combined with asthma, suspected food or drug allergies, or recurrent sinus infections that may be allergy-related.

Seek immediate emergency care for any signs of anaphylaxis, including difficulty breathing, throat tightening, widespread hives with swelling, rapid or weak pulse, dizziness, or fainting after allergen exposure. If you have a known risk of anaphylaxis, your doctor should prescribe epinephrine auto-injectors and help you create a written anaphylaxis action plan. The AAAAI recommends that all patients who have experienced anaphylaxis carry two epinephrine auto-injectors at all times and wear medical identification jewelry [9].

How Can You Prevent Allergic Reactions?

Prevention focuses on minimizing exposure to known allergens through environmental controls, dietary vigilance for food allergies, and pre-medicating before anticipated exposure. Allergen immunotherapy is the only treatment that can modify the underlying disease process and potentially prevent new allergies and asthma from developing.

Environmental control measures are the cornerstone of allergy prevention. For indoor allergens, use HEPA vacuum filters, remove carpeting where possible, keep pets out of bedrooms, control humidity to prevent mold growth, and replace HVAC filters regularly. For outdoor allergens, check daily pollen forecasts through the National Allergy Bureau, limit outdoor activities during peak pollen hours (typically early morning), wear wraparound sunglasses to protect eyes, and change clothes and shower after spending time outdoors.

For food allergies, careful label reading is essential. The Food Allergen Labeling and Consumer Protection Act requires clear labeling of the nine major allergens on packaged foods, though advisory statements like 'may contain' are voluntary and inconsistent. When dining out, communicate your allergies clearly to restaurant staff, ask about ingredients and cross-contamination risks, and carry your epinephrine auto-injector at all times.

Research from the LEAP study published in the New England Journal of Medicine demonstrated that early introduction of peanut-containing foods to high-risk infants between 4 and 11 months of age reduced the risk of developing peanut allergy by 81 percent (Source: Du Toit et al., NEJM, n=640) [5]. This landmark finding changed international guidelines — the American Academy of Pediatrics and NIAID now recommend early introduction of peanut products for high-risk infants rather than avoidance. Talk to your pediatrician before introducing common allergens to high-risk babies.

The LEAP trial showed early peanut introduction reduced peanut allergy risk by 81 percent in high-risk infants [5]

What Questions Should You Ask Your Doctor About Allergies?

Preparing specific questions before your allergy appointment helps you get the most useful information and make informed decisions about your care. Here are the most important questions to bring up, along with why each one matters.

Understanding your specific diagnosis and triggers is the foundation of effective allergy management. Ask your doctor to explain exactly which allergens you tested positive for and which ones are most likely causing your worst symptoms. This helps you prioritize avoidance strategies and choose the right medications.

• Which specific allergens did I test positive for, and which are causing my worst symptoms? — Helps you prioritize avoidance efforts and targeted treatment
• Should I try immunotherapy (allergy shots or sublingual tablets)? — Immunotherapy is the only treatment that can modify the underlying disease, but it requires a 3-to-5-year commitment
• Could my allergies be contributing to my asthma, sinusitis, or ear infections? — Allergies often drive other conditions, and treating the allergies can improve them all
• Are there any medications I should avoid because of my allergies? — Drug cross-reactivity is common (e.g., penicillin allergy may extend to related antibiotics)
• What should my emergency plan look like if I have a severe reaction? — Every patient at risk of anaphylaxis needs a written action plan and epinephrine auto-injectors
• Should my children be tested, given my allergy history? — Allergies have a strong genetic component, and early identification can guide prevention strategies like early allergen introduction