Can allergies cause a runny nose?

How allergies cause it

An allergic runny nose tends to come on fast. Hay fever symptoms can begin immediately after you are exposed to allergens like pollen or animal dander, and they continue as long as the exposure does.¹ Early symptoms of allergic rhinitis, a runny nose among them, begin almost immediately after exposure to the allergen, while in the later phase the most dominant symptom is a stuffy nose.³

The flow is the end of a chain reaction in the immune system. If you have allergic rhinitis, your immune system overreacts to the allergen by making antibodies called immunoglobulin E (IgE). These antibodies travel to cells that release histamine and other chemicals, which cause a runny nose along with sneezing, stuffiness, itching and postnasal drip.² Within minutes of exposure, mast cells release histamine and other chemicals, and histamine provokes virtually all of the early symptoms.³

With a pollen allergy, the discharge is usually clear and thin. A runny nose is also known as rhinorrhea.⁵

Seasonal symptoms in spring, summer and early fall are usually caused by airborne mold spores or pollen from trees, grass and weeds. Year-round symptoms are generally caused by dust mites, pet hair or dander, cockroaches or mold.¹ More than two-thirds of people with seasonal allergies also have symptoms year-round.⁴

Allergies or something else?

It can be hard to tell a cold from hay fever, but the discharge and your temperature give clues. If you have hay fever, your runny nose will likely have a thin, watery discharge, and you will not have a fever. With a cold, you may have a thicker or yellowish discharge and a low-grade fever.¹

Color can change with a cold, too. During a cold, mucus may change to a white, yellow or green color after 2 or 3 days, and CDC says this is normal.⁹

Allergy symptoms usually last as long as you are exposed to the allergen, which may be about 6 weeks during pollen season. Colds and flu rarely last beyond 2 weeks.¹⁰ A stuffy, runny nose is also common with a cold and sometimes comes with the flu.¹⁰

Many people with rhinitis symptoms do not have allergies. Non-allergic rhinitis usually begins in adults and causes year-round symptoms, especially a runny nose and stuffiness. Strong odors, pollution, weather changes, smoke and other irritants may cause its symptoms.²

When to see a doctor

If a cold seems to be behind your runny nose, CDC advises seeking medical care for trouble breathing or fast breathing, dehydration, a fever that lasts longer than 4 days, symptoms that last more than 10 days without getting better, symptoms such as fever or cough that improve and then return or worsen, or chronic medical conditions that get worse.¹¹

A runny nose can also be an early, mild sign of anaphylaxis, a rare but severe allergic reaction most often linked to allergies to food, insect stings, drugs and latex.¹² Those early symptoms can quickly lead to more serious problems, including trouble breathing, tightness of the throat and dizziness, and anaphylaxis can be deadly.¹²

To find the cause of allergy symptoms, an allergist may start by taking a detailed history, looking for clues in your lifestyle that help pinpoint the cause.¹ If the symptoms appear at work or get worse there, ACAAI suggests asking an allergist to help identify the triggers.¹