COVID-19 rapid testing has become a common practice, but the question of whether everyday nasal products interfere with the results remains a frequent concern. A nasal spray can potentially affect a COVID-19 test result, but this outcome is highly dependent on the type of spray used and the specific test being performed. The interference is mainly a risk with at-home rapid antigen tests (RATs), which are more susceptible to chemical and physical disruption than laboratory-based tests. Understanding how these components interact with the testing mechanisms is necessary to ensure the accuracy of a result.
Specific Nasal Spray Ingredients That Interfere
The components most likely to cause a false-positive result are not the active medications but the inactive ingredients designed to stabilize the formula or moisturize the nasal passage. Many medicated or moisturizing sprays contain mucoadhesive polymers, which are substances that allow the product to stick to the nasal lining for a longer time. Ingredients like sodium carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), and various other thickening agents are used to increase the spray’s viscosity.
These polymers can physically interfere with the testing process by changing the fluidity of the sample. Furthermore, the presence of certain buffers, preservatives, or ions within the spray can alter the chemical environment of the nasal sample. When these foreign substances are introduced into the sensitive environment of a rapid test, they can trigger a non-specific reaction that mimics the presence of the SARS-CoV-2 antigen. Simple saline sprays are less likely to cause a false positive, but they can lead to a false negative result by significantly diluting the viral load collected on the swab.
How Nasal Sprays Interact with Different COVID Tests
Rapid Antigen Tests (RATs)
The primary vulnerability lies in the mechanism of the Rapid Antigen Test (RAT), which is a type of lateral flow immunoassay. A RAT functions by using specialized gold nanoparticles coated with antibodies that bind specifically to the SARS-CoV-2 nucleocapsid protein. When a nasal spray component, such as a polymer or an acidic substance, is present, it can disrupt the test cassette’s internal environment. This disruption can cause the gold nanoparticles to aggregate or bind non-specifically to the test line, resulting in a false-positive line even without the presence of the viral antigen.
The buffer solution provided in the test kit is specifically formulated to maintain a neutral pH and regulate the flow of the sample across the test strip. Introducing foreign chemicals can neutralize this stabilizing effect, leading to inaccurate results. The change in viscosity from thickening agents can also impede the flow rate across the strip, potentially leading to an invalid or inaccurate result.
Polymerase Chain Reaction (PCR) Tests
In contrast, Polymerase Chain Reaction (PCR) tests, which are performed in a laboratory, are generally less susceptible to interference leading to a false positive. PCR tests detect the virus’s genetic material (RNA) through an amplification process, making them highly sensitive and specific. For these tests, nasal spray use is more likely to cause a false negative or an invalid result.
Certain spray ingredients, such as some preservatives or high concentrations of thickeners, can inhibit the enzymes required for the PCR amplification process. Excessive irrigation, such as with a Neti pot or large-volume saline rinse, can also dilute the viral load below the detection limit. This dilution of the sample collected on the swab could result in a false negative result.
Steps to Ensure Accurate Testing
To ensure the most reliable COVID-19 test result, timing the nasal spray use is important, especially when using an at-home antigen test. Experts recommend a waiting period between the application of any nasal spray—whether medicated, moisturizing, or simply saline—and the collection of the nasal sample. A waiting time of 30 to 60 minutes is generally advised to allow the contents of the spray to be absorbed or cleared from the nasal passages by the body’s natural mucociliary clearance.
If you regularly use a spray, it is best practice to gently blow your nose before swabbing to clear any residual product or mucus. It is also important to strictly follow the manufacturer’s instructions for the specific test kit, particularly concerning the amount of buffer solution to use and the correct swabbing technique. If a positive result occurs immediately after using a nasal spray, especially without any symptoms, retesting is a prudent step. Retesting after the recommended waiting period or confirming the result with a laboratory-based PCR test can help rule out a potential false positive caused by product interference.