What are the symptoms of an allergy?

Sneezing, a runny or stuffy nose, itchy or watery eyes, and itchy skin, rashes, or swelling are common allergy symptoms. Coughing and wheezing can occur too. The pattern depends partly on the trigger and where the reaction develops. Trouble breathing, difficulty swallowing, or signs of circulatory collapse can signal a severe reaction that needs immediate help.

The symptoms of an allergy

An allergy occurs when the immune system reacts to a substance that causes no problems for most people. Symptoms can affect different parts of the body: the nose runs or becomes congested, eyes itch or water, and skin develops itching, swelling, or a rash. Sneezing and asthma symptoms can also be part of the picture. Reactions range from mild to severe.

In 2024, 31.7% of US adults had a diagnosed seasonal allergy, eczema, or food allergy. That figure shows how common these conditions are, but it cannot tell you whether a particular unexplained symptom is allergic. Bottoms-McClain et al., 2026.

The most common allergy symptoms

Allergens can produce symptoms in several areas of the body. Two people exposed to the same pollen may therefore have different experiences. Timing varies as well: some symptoms begin soon after exposure, while others develop later. MedlinePlus: allergic rhinitis.

Area	Common symptoms	Typical context
Nose	Sneezing, runny nose, congestion	Exposure to pollen, dust mites, or animal allergens
Eyes	Watering, itching, dark circles, swelling	Airborne allergens indoors or outside
Skin	Rashes, swelling, itching, hives	Contact reactions, food allergy, or insect stings
Digestion	Abdominal pain, nausea, vomiting, diarrhea	Food allergy; a US adult survey estimated its prevalence at 10.8%
Airways	Coughing, wheezing, asthma symptoms	Pollen, mold, dust mites, or pet allergens
Other symptoms	Fatigue, headaches, sore throat, blocked ears, reduced sense of smell	Ongoing exposure, including a prolonged pollen season

The 10.8% estimate concerns food allergy overall, not the percentage of adults with digestive symptoms. It was based on a survey’s symptom criteria rather than food-challenge confirmation in every participant. Table sources: MedlinePlus: allergic rhinitis, MedlinePlus: allergy, MedlinePlus: anaphylaxis, and Gupta et al., 2019. For nighttime discomfort, see sleeping with a sore throat.

Fatigue, headaches, and blocked ears may be less obvious than sneezing, but can also accompany allergy. Studies of allergic rhinitis, often called hay fever, have linked it with poorer sleep quality, daytime sleepiness, and morning headaches. The evidence for these associations was rated low to very low quality. The findings do not establish that rhinitis caused those problems. Liu et al., 2020.

Why allergies cause these symptoms

During an allergic reaction, the immune system responds to a normally harmless substance as a threat. In allergic rhinitis, an inhaled allergen encounters IgE antibodies attached to mast cells in the nasal lining. The immune system must already be sensitized to that substance. Mast cells then release histamine and other signaling molecules that produce symptoms. Zoabi et al., 2022.

This helps explain why the nose and eyes are often affected together. Allergic rhinitis is an IgE-mediated response to an inhaled allergen and frequently coexists with allergic conjunctivitis and asthma. Bousquet et al., 2020.

A runny nose is not always allergic, however. A review of studies reported a median prevalence of 18.1% for allergic rhinitis and 29.4% for rhinitis without specifying its cause. The median is the middle value when estimates are ranked. Definitions and populations varied substantially, so these are not a single universally applicable rate or a direct diagnostic comparison. Exposure history remains important when investigating nasal symptoms. Savouré et al., 2022.

What triggers allergy symptoms?

Substances that trigger allergic reactions are called allergens. Someone can react to more than one. MedlinePlus: allergy.

• Airborne allergens include pollen, dust mites, mold spores, and pet dander. Symptoms can follow exposure. MedlinePlus: allergic rhinitis.
• Among US adults in the 2015–2016 food allergy survey, shellfish allergy was most common at 2.9%, followed by milk at 1.9% and peanut at 1.8%. These were population estimates based on symptom-defined convincing allergy. Gupta et al., 2019.
• Insect stings can cause local swelling or a severe, life-threatening allergic reaction. MedlinePlus: allergy.
• Drug allergies can also range from mild to severe. MedlinePlus: allergy.

Allergy can first appear in adulthood. In the same survey, 48% of adults with convincing food allergy reported that at least one of their food allergies began as an adult. This does not mean that all of them had been free of food allergy during childhood. A first recognized reaction can be severe. Gupta et al., 2019.

Signs of a severe allergic reaction

Anaphylaxis is a potentially life-threatening systemic allergic reaction. Symptoms can develop rapidly, sometimes within seconds or minutes, and may involve several parts of the body. The following six groups describe possible features, not a checklist that must be completed before seeking help. MedlinePlus: anaphylaxis and Cardona et al., 2020.

• Breathing: shortness of breath, coughing, wheezing, or high-pitched breathing sounds. MedlinePlus: anaphylaxis.
• Swelling: swelling of the face, eyes, or tongue, especially with difficulty swallowing or airway symptoms.
• Circulation: dizziness, lightheadedness, faintness, or palpitations.
• Skin: hives, itching, or flushing.
• Digestion: abdominal pain, nausea, vomiting, or diarrhea.
• Consciousness and speech: slurred speech or loss of consciousness.

These signs may appear in different combinations. Hives or flushing alone do not automatically mean anaphylaxis, and anaphylaxis can occur without a rash. If breathing, swallowing, or circulation is affected after a suspected allergen exposure, do not wait for more symptoms to appear.

When to call for emergency help and when to book an appointment

For a suspected severe allergic reaction, call 911 in the United States or 112 in Germany immediately. Warning signs include trouble breathing, swelling that may affect the airway, difficulty swallowing, or dizziness with impending fainting. Use a prescribed epinephrine auto-injector immediately if available; do not wait for a test or for emergency responders to arrive. MedlinePlus: anaphylaxis.

Clinicians recognize anaphylaxis from symptoms and examination findings. Emergency treatment does not wait for a confirmatory test. Epinephrine injected into a muscle is first-line treatment in the cited anaphylaxis guidelines. Once the emergency has been treated, a specialist can investigate the trigger and help plan for future reactions. Cardona et al., 2020 and Muraro et al., 2022.

Recurring symptoms deserve assessment even when they are not an emergency. So do symptoms that are no longer adequately controlled by usual treatment. A clinician can consider whether allergy fits the pattern and whether an allergy test would help. MedlinePlus: allergic rhinitis.

Allergy, a cold, or sinusitis?

No single symptom reliably separates these conditions. The combination of symptoms, their timing, and their duration is more informative. Allergy symptoms may begin soon after exposure. A cold generally begins a few days after infection with one of more than 200 possible viruses. MedlinePlus: allergic rhinitis and MedlinePlus: common cold.

Feature	Allergies	Common cold	Sinusitis
Onset	Often soon after allergen exposure	A few days after infection	Often follows a cold
Duration	May persist while exposure continues	Some symptoms last 10–14 days	Acute: up to 4 weeks
Fever	Not a feature of ordinary hay fever	Can occur, though uncommon	Can occur
Itching	Itchy nose, eyes, or throat is characteristic	Not a defining feature	Not a defining feature
Pattern, frequency, or longer-duration categories	Intermittent or persistent	Adults average 2–3 colds a year	Subacute: 4–12 weeks; chronic: more than 12 weeks

The fever distinction concerns ordinary respiratory allergies such as hay fever, not every possible immune or drug reaction. NIH comparison.

The last row contains different kinds of information: an allergy pattern, the average frequency of colds, and duration-based sinusitis categories. They are useful context, not directly comparable measurements. More than one condition can be present at the same time.

Table sources: MedlinePlus: common cold, MedlinePlus: sinusitis, MedlinePlus: allergic rhinitis, and Bousquet et al., 2020. For nighttime discomfort, see sleeping with a sinus infection.

The distinction is not always straightforward even in clinical practice. A systematic review of patients with suspected acute rhinosinusitis found imaging-confirmed inflammation in 51%, while 31% met a reference standard for acute bacterial rhinosinusitis. The bacterial assessment used pus on sinus puncture or a positive bacterial culture, not imaging alone. Individual signs had limited diagnostic accuracy. These figures apply to patients already suspected of having acute rhinosinusitis, not everyone with a runny nose. Ebell et al., 2019.

Allergies can also contribute to sinus inflammation, so the conditions are not mutually exclusive. The course over time and the overall clinical picture often help more than one isolated symptom. MedlinePlus: sinusitis.

How long do allergy symptoms last?

Symptoms can continue while allergen exposure continues, so there is no fixed number of days. Allergic rhinitis is classified as intermittent or persistent, and separately as mild or moderate to severe. These descriptions help capture how often symptoms occur and how much they interfere with life. Bousquet et al., 2020.

Within an episode, itching of the nose, eyes, or throat, sneezing, a runny nose, and watery eyes often appear early. Congestion, cough, blocked ears, reduced smell, sore throat, fatigue, and headaches may develop later. This sequence alone cannot identify the allergen. MedlinePlus: allergic rhinitis.

How allergies are investigated and confirmed

Not every suspected allergy is confirmed. In a US survey, 19% of adults reported a food allergy, while 10.8% described symptoms meeting the study’s criteria for a convincing food allergy. This was not the same as confirming every diagnosis with a supervised food challenge. Gupta et al., 2019.

• Start with the history. Symptoms, timing, and suspected exposures guide the choice of tests. For persistent or poorly controlled rhinitis, skin testing or serum specific IgE may help clarify an allergic cause. A suspected food or drug reaction needs assessment on its own merits; it should not have to persist before being investigated. Bousquet et al., 2020.
• Skin-prick testing is a first-line approach in many suspected IgE-mediated allergies. It is not the test for every type of allergic reaction. Ansotegui et al., 2020.
• Specific IgE blood tests can complement skin testing or be used when skin testing is unsuitable. Ansotegui et al., 2020.
• A medically supervised oral food challenge is the reference standard for food allergy diagnosis and is particularly useful when the history and test results leave uncertainty. The food is given under medical supervision, not tried at home as a diagnostic experiment. Santos et al., 2023.

A positive skin-prick or specific IgE test initially shows sensitization. Diagnosing allergy also requires clinically relevant symptoms triggered by that allergen. Ansotegui et al., 2020.

Frequently asked questions

What are seven common allergy symptoms?

Common symptoms can be grouped as sneezing; a runny nose; a stuffy nose; itchy or watery eyes; itchy skin or rashes; swelling; and coughing or wheezing. They do not all have to appear together.

Itching, sneezing, a runny nose, and watery eyes often begin soon after exposure. Congestion, cough, and fatigue may follow later. The pattern varies with the trigger and the tissues involved, and symptoms can range from mild to severe. MedlinePlus: allergy and MedlinePlus: allergic rhinitis.

What are five signs of a severe allergic reaction?

Possible features include five broad groups: breathing difficulty or wheezing; facial or tongue swelling with swallowing difficulty; dizziness or palpitations; hives with flushing; and slurred speech or loss of consciousness. They can develop rapidly after exposure. These groups are a description, not diagnostic criteria: isolated hives do not by themselves establish anaphylaxis, and a severe reaction can occur without skin changes.

For suspected anaphylaxis, call 911 in the United States or 112 in Germany immediately. Use a prescribed epinephrine auto-injector if available. Intramuscular epinephrine is first-line emergency treatment in the cited guidance. MedlinePlus: anaphylaxis and Cardona et al., 2020.

How can you tell an infection from an allergy?

Timing and accompanying itching offer clues. Allergy symptoms can begin soon after exposure, often with an itchy nose, eyes, or throat. A cold begins a few days after infection with one of more than 200 possible viruses, and some symptoms can last 10–14 days.

Even clinicians may need the full history and examination to distinguish causes. In studies of suspected acute rhinosinusitis, imaging confirmed inflammation in 51%, and a separate puncture or culture reference standard supported bacterial rhinosinusitis in 31%. These numbers describe that selected population; they cannot determine whether your symptoms are allergic or infectious. MedlinePlus: common cold, MedlinePlus: allergic rhinitis, and Ebell et al., 2019.

Can allergies cause a sore throat?

Yes. Sore throat can occur later in an episode of allergic rhinitis, along with congestion, cough, blocked ears, and reduced smell. Symptoms continuing through weeks of pollen exposure may fit that pattern better than a single cold. The pattern alone does not establish the cause. MedlinePlus: allergic rhinitis.

Can allergies cause headaches?

Headaches can accompany allergic rhinitis. Along with fatigue and irritability, they may appear later than sneezing and itching. Observational studies also associate rhinitis with poorer sleep, daytime sleepiness, and morning headaches, but the evidence was rated low to very low quality. That does not establish a causal chain in which rhinitis disrupts sleep and thereby causes headache. MedlinePlus: allergic rhinitis and Liu et al., 2020.

Can allergies cause a fever?

Ordinary hay fever does not cause fever. Fever alongside nasal allergy symptoms suggests another process, such as an infection. NIH comparison of respiratory symptoms. Sinusitis can involve fever, weakness, and fatigue, whereas sneezing, itching, and congestion are characteristic of allergic rhinitis.

Allergy and sinusitis can coexist. If fever develops after prolonged nasal symptoms, a clinical assessment can help identify what has changed. MedlinePlus: allergic rhinitis and MedlinePlus: sinusitis.

Can allergies begin in adulthood?

Yes. In a US survey, 48% of adults with convincing food allergy reported that at least one food allergy began in adulthood. Some also had childhood-onset allergies. Overall, 10.8% met the survey’s symptom criteria for convincing food allergy, while 19% believed they had a food allergy. These measures are different, and neither means every participant had a food-challenge-confirmed diagnosis. Gupta et al., 2019.

Diagnosed allergic conditions are also common more broadly: in 2024, 31.7% of US adults had a diagnosed seasonal allergy, eczema, or food allergy. Bottoms-McClain et al., 2026.

How do clinicians test for allergies?

The history comes first. Symptoms and previous reactions help determine which tests are appropriate. With persistent or poorly controlled rhinitis, skin-prick testing or serum specific IgE can help investigate an allergic cause. Other suspected reactions, including food and drug reactions, need their own assessment rather than waiting for symptoms to become persistent.

Skin-prick testing is first-line in many IgE-mediated allergies. Specific IgE blood tests can complement it or provide an alternative when appropriate. For an uncertain food allergy diagnosis, a medically supervised oral food challenge is the reference standard. A positive skin or IgE test alone shows sensitization; allergy requires corresponding symptoms on exposure. Ansotegui et al., 2020, Bousquet et al., 2020, and Santos et al., 2023.

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