Can Allergies or the Common Cold Cause a Positive Antigen Test Result?
When discussing antigen tests, most people are referring to rapid diagnostic tests for the SARS-CoV-2 virus—the pathogen responsible for COVID-19. A common question arises: can conditions like allergic rhinitis or the common cold lead to a positive result, showing two lines (or "two bars") on a rapid antigen test? The straightforward answer is no—neither allergies nor typical viral colds alone will trigger a positive antigen result. These conditions do not involve the presence of the SARS-CoV-2 virus, which is what the test is designed to detect.
How Do Rapid Antigen Tests Work?
Rapid antigen tests identify specific proteins from the SARS-CoV-2 virus, such as the nucleocapsid (N) protein, spike (S) protein, membrane (M) protein, or envelope (E) protein. These proteins are present when an active infection exists in the body. The test works on the principle of antigen-antibody binding: if viral antigens are present in the nasal or throat sample, they bind to antibodies on the test strip, triggering a visible line in the T (test) region.
A positive result appears as two colored lines—one in the C (control) zone and one in the T (test) zone. This dual-line outcome indicates the likely presence of SARS-CoV-2 antigens. However, this only occurs if the individual is currently infected with the coronavirus—not due to seasonal allergies, hay fever, or non-COVID respiratory infections.
When Might Someone With a Cold or Allergies Get Two Lines?
The only scenario in which a person suffering from nasal congestion, sneezing, or other cold-like symptoms would test positive is if they are simultaneously infected with SARS-CoV-2. Many respiratory illnesses share similar symptoms, including runny nose, sore throat, and fatigue. Therefore, someone might mistake early signs of COVID-19 for a routine cold or allergy flare-up.
If that individual has recently been exposed to a confirmed case of COVID-19 or visited a high-risk area, the appearance of two lines could indicate a true co-infection—or more accurately, a misinterpreted initial assumption about the cause of their symptoms. In such cases, the immune system is responding to the coronavirus, not allergens or rhinoviruses (common cold viruses).
Understanding Negative Results
In individuals who have allergies or a standard cold but are not infected with SARS-CoV-2, the antigen test will typically show only one line—the control line (C). This single line confirms that the test was performed correctly but that no viral antigens were detected. It's a reliable negative result when interpreted properly.
It's important to note that while rapid antigen tests are convenient and fast, they are less sensitive than molecular tests, especially during the early or late stages of infection when viral loads may be low.
For Greater Accuracy: Consider PCR Testing
If you're experiencing symptoms consistent with COVID-19—even mild ones—and have had potential exposure, health experts recommend confirming results with a polymerase chain reaction (PCR) test. Unlike antigen tests, PCR tests amplify genetic material from the virus, allowing detection even at very low levels. This makes them significantly more accurate, particularly in asymptomatic individuals or those in the incubation phase.
Therefore, if there's any doubt about your status—especially when living with vulnerable populations or preparing to travel—a follow-up PCR test provides greater confidence in your diagnosis.
Final Thoughts: Symptom Overlap Doesn't Mean Test Confusion
While allergic rhinitis and the common cold can mimic some symptoms of COVID-19, they do not interfere with or alter the outcome of a rapid antigen test. A two-line result is not caused by mucus, inflammation, or histamine responses—it specifically signals the presence of SARS-CoV-2 proteins.
Stay informed, monitor your symptoms carefully, and when in doubt, opt for lab-based testing to ensure accuracy. Public health decisions should always be based on reliable diagnostics, not assumptions—even if your sniffles feel all too familiar.