FULL CLAIM: Poison Control Centres alert about a toxic chemical called sodium azide in home COVID-19 testing kits. “Just another one the Conspiracy Theorists called correctly - PCR testing is not good for anyone.”
REVIEW
A Facebook reel posted in early 2025 claimed that at-home COVID-19 testing kits contain harmful substances. Specifically, the reel’s caption claimed that U.S. Poison Control Centers had alerted people about a “poisonous substance” in test kits called sodium azide. The caption added, “Just another one the Conspiracy Theorists called correctly – PCR testing is not good for anyone”.
The video accompanying this caption followed the same narrative, throwing suspicion over the fact that test swabs glow under blacklight. “What are they putting in the COVID tests so that you take these twenty thousand times and stick them up your nose?”, the video asked.
Two instances of the reel received considerable engagement on Facebook. One of them was posted by Linda Traitz, a user with around 150,000 followers, and received over 160,000 views. The other one was posted on “The Rabbit Hole”, a Facebook page with almost half a million followers that posts conspiracy theories, and was viewed more than 150,000 times.
Misinformation about test swabs was recurrent during the COVID-19 pandemic, involving false claims that swabs contained nanobots, parasites, radioactivity, and toxic substances such as ethylene oxide or lithium. The Facebook reel is yet another example of such a narrative.
First, the reel confuses rapid antigen tests with PCR tests, which are different techniques. Second, the reel’s content is misleading because it implies that the presence of sodium azide in COVID-19 antigen test kits means testing is harmful to people. This isn’t true.
U.S. Poison Control Centers did alert people about a reagent in rapid COVID-19 antigen tests in 2022. However, neither this warning nor the fact that test swabs glow under blacklight indicates that at-home COVID-19 tests are harmful. We explain why below.
Users shouldn’t come into contact with the tiny amounts of sodium azide present in some rapid COVID-19 tests
Sodium azide is a colorless and odorless solid that is highly soluble in water and has multiple applications. For example, it is used as a pest control agent and as a preservative in some diagnostic medicines and blood tests. When mixed with water or acids, sodium azide becomes a powerful explosive that is used as a propellant for inflating car airbags.
Sodium azide is highly toxic, and inhaling or touching it causes eye, skin, and respiratory tract irritation. Swallowing even small amounts of sodium azide can result in a transient drop in blood pressure that can lead to heart palpitations, dizziness, headache, nausea, and vomiting. Cases of severe poisoning can result in loss of consciousness or even death.
Rapid COVID-19 antigen tests typically contain a nasal swab, a vial with reagent fluid, and a testing strip. The reagent fluid consists of a saline solution with small amounts of buffering chemicals that keep the pH of the fluid stable. The reagent fluid in some kits also contains tiny amounts of sodium azide that works as a preservative and also helps transfer the sample from the swab to the reagent liquid.
But sodium azide is only present in the reagent fluid, not in the nasal swabs. This means that if the kit is correctly handled and disposed of, the person taking the test doesn’t ever come into contact with sodium azide.
However, the vials of reagent fluid may visually resemble eye droppers and other medications, which may lead some people to accidentally ingest their content or use it on their eyes or skin. A 2022 letter published in the American Journal of Emergency Medicine found that around 150 cases of exposure to COVID-19 test kit reagents were reported to U.S. Poison Control Centers between July 2021 and January 2022[1]. The authors noted that many cases resulted in minor or no adverse effects, indicating that the low amounts of sodium azide present in the reagent fluid “are unlikely to cause significant human toxicity” in adults. A similar study conducted in Australia in 2023 arrived at the same conclusion[2].
The case is different for small children, who due to their smaller body size are particularly susceptible to adverse effects including sudden drops in blood pressure and fainting if they accidentally swallow reagent fluid. This is the main reason why Poison Control Centers around the U.S. alerted people to the presence of sodium azide in COVID-19 test kits in early 2022.
Susan Smolinske, the director of the New Mexico Poison & Drug Information Center and co-author of the letter in the American Journal of Emergency Medicine, explained that the message isn’t to stop using rapid kits but to “just be careful with these reagents”. This means using them as indicated and keeping them out of children’s reach.
Glowing under black light is an innocuous physical property of many materials
The fact that test swabs glow under black light does also not indicate they contain any harmful or suspicious hidden component.
Black light is a type of ultraviolet (UV) radiation that emits very little visible light (Figure 1). This type of light has many applications, from attracting insects—some of which can see UV light—to disinfecting medical material to diagnosing some infections and diseases.
Figure 1 – Diagram of the electromagnetic spectrum, showing the variation in wavelength, frequency, and energy at the different ranges. The narrow range of visible light is shown enlarged at the top. Source: U.S. National Aeronautics and Space Administration (NASA)
Most materials exposed to black light absorb the UV radiation and reflect only a small part of it, also as UV light invisible to the human eye. However, some materials contain phosphors, which are molecules that can absorb UV radiation and re-emit it at longer wavelengths. These longer wavelengths are visible to the human eye, causing the material to appear to glow. This phenomenon called luminescence may occur while the source of light is present (fluorescence), or persist for minutes to days after the light source has been removed (phosphorescence).
Many common materials and even living organisms glow under black light. Some examples include ripe bananas, tonic water, some vitamins, and plant chlorophyll. Also, certain body fluids like saliva, urine, semen, and vaginal fluid naturally emit fluorescence, a property that is extremely useful in forensic investigations[3].
In other words, luminescence is a relatively common phenomenon, and there are many possible explanations of why test swabs may glow under black light. These go from the materials the swabs are made of to specific treatments these materials may have received or simple contamination with luminescent materials during handling.
Regardless of the cause, this characteristic isn’t proof positive that a harmful substance is present, but a normal physical phenomenon associated with many common substances and materials.
REFERENCES
- 1 – Johnson-Arbor et al. (2022) Human toxicity from COVID-19 rapid home test kits. American Journal of Emergency Medicine.
- 2 – Chiew et al. (2023) Clinical features of COVID-19 rapid antigen test exposures reported by an Australian poisons information centre: a prospective study. Clinical Toxicology.
- 3 – Achetib et al. Specific fluorescent signatures for body fluid identification using fluorescence spectroscopy. Scientific Reports.
