Besides certain distinct symptoms, sinus infections and allergies have other key differences:

Causes

Allergies: Allergies occur due to an overactive immune response to allergens like pollen or dust. When activated, the immune system releases histamines, chemicals that cause sneezing and increased mucus production. Other chemicals set the inflammation process in motion, leading to nasal congestion and swelling.

Sinus infection: Sinus infections can occur due to an upper respiratory infection affecting the nose or throat, caused by viruses or bacteria. The sinuses, which run behind the eyes, cheeks, nose, and forehead, become inflamed and blocked. Mucus builds up in the sinuses, causing pain or pressure. Bacteria enter the body through the nose, mouth, or eyes, growing in the blocked mucus.

Viral infections are the most common cause of sinus infections in people with a healthy immune system. People with weakened immune systems can develop sinus infections from fungi or bacteria, which may cause more serious health concerns.

Predictability

Allergies: Allergies can be perennial (all year round) or seasonal. Indoor allergens like dust, pet dander, and mold typically cause perennial allergies. Seasonal allergies tend to flare up during the spring, summer, or fall, when tree or grass pollens begin to multiply. Ragweed blooms from August through November and is the most common cause of fall seasonal allergies. 

People with seasonal allergies can often predict when their symptoms will get worse. They can then take precautions to avoid outdoor allergens.

Sinus infections: Sinus infections are often unpredictable. They can occur anytime someone has swelling and mucus buildup in their sinuses.

Treatments

Allergies: The best treatment for allergies is avoiding the allergen that causes symptoms. Treatments like antihistamines, steroid nasal sprays and immunotherapy (allergy shots) can help reduce swelling and other allergy symptoms.

Sinus infection: How to treat a sinus infection depends on its cause. With virus-based sinus infections, the infection typically clears on its own with plenty of rest. Healthcare providers sometimes suggest or prescribe corticosteroid nasal sprays and anti-inflammatory medicines.

If the cause is allergies, allergy treatment will help avoid future infections. If bacteria caused your sinusitis or a bacterial infection developed from the mucus buildup, you may need antibiotics to clear the infection.

Despite their differences, some similarities between allergies and sinus infections can make them hard to distinguish:

Common Conditions

Up to 1 in 6 people live with allergic rhinitis. It is one of the most common chronic disorders among children and is very common in people ages 20-40.

Sinus infections are one of the leading reasons for antibiotic prescriptions. They are most common in children younger than 15 and adults aged 25-64.

Acute, Chronic, or Recurring

Acute (short-term) allergies occur when someone comes into contact with something they’re allergic to. Symptoms typically go away when the allergen is no longer present. Seasonal allergies cause recurring (repeated) allergy symptoms in periods when certain trees or grasses bloom. Perennial allergies often cause chronic (long-term) allergy symptoms because allergens are always present. 

Sinusitis is considered acute when it lasts less than four weeks. If symptoms last 12 or more weeks, it’s become chronic. Some people have recurring sinusitis, four or more episodes of acute sinusitis in the same year.

Share Some Treatments

While some treatments are specific to each condition, the two share some options.

Allergies and sinus infections involve swelling in the nasal passages. Medications like corticosteroids and decongestants can help reduce swelling and open the sinuses for both conditions. Steam, warm compresses, and saline nasal sprays or rinses can help relieve sinus pain and pressure.

It’s possible to have allergies and a sinus infection at the same time because they have different causes. Allergies can also cause a sinus infection when nasal congestion leads to blocked mucus and bacterial growth in the sinuses.

It can be hard to tell whether allergies have turned into a sinus infection. If you develop a fever or, in some cases, thick or discolored mucus, you may have developed sinusitis on top of your allergies.

A primary care provider or pediatrician can diagnose allergies and sinus infections. However, these providers may need to refer you to an allergist or ear, nose, and throat (ENT) specialist, who can test for specific allergies or treat any complications.

If you have mild allergy symptoms, you may be able to manage them yourself with over-the-counter (OTC) medications like Zyrtec (cetirizine) and saline rinses. However, if symptoms become more severe, make an appointment with your provider.

Call a healthcare provider right away if you or your child has any of the following:

• Severe pain
• A fever that lasts longer than four days
• Symptoms that last longer than 10 days
• Symptoms that improve but then get worse again

Allergies and sinus infections share several symptoms but often have different causes and treatments.

Allergies happen when your immune system reacts to allergens like pollen, while sinus infections most commonly result from viruses or bacteria.

Knowing the difference between the two conditions can help you choose the right treatment and feel better faster.