# The swabs and brushes used in medical tests are sterilised with a cancer-causing gas, so having a cervical smear or a Covid test exposes you to a carcinogen **Verdict: Contradicted.** The chemistry in this claim is real and the conclusion drawn from it is not. Ethylene oxide is a gas used worldwide to sterilise medical devices, and overexposure to it genuinely can cause cancer and lung damage, which is why occupational exposure is tightly controlled. None of that establishes that a device sterilised with it carries a risk to the patient who touches it, and the regulator says plainly that it does not. Asked about the cervical screening version in August 2026, a spokesperson for the UK's Medicines and Healthcare products Regulatory Agency told Full Fact there is no credible evidence that the swabs used in cervical smear tests are associated with cancer. The mechanism is the ordinary one for a processing agent: the gas is applied, then removed, and what remains is capped by an international standard and tested for before the device can be sold. What this file rates is not whether ethylene oxide is hazardous, because it is; it is the claim that being sterilised with it makes a swab or brush dangerous to the person it is used on. That claim is false. This is a record of what regulators and researchers have said, not health advice, and decisions about screening belong with a clinician and with health services such as the NHS. Category: Science, Space & Technology · Era: 2020s · First circulated: Spring 2021, when posts urged people not to use Covid-19 lateral flow tests because the swabs were sterilised with ethylene oxide; the cervical screening version spread across Facebook, Instagram and X in August 2026 · Believed by: A wide audience reached through wellness and natural-health networks, alongside people with no particular views on medicine who encounter a screenshot naming a real carcinogen and reasonably want to know whether it is in something about to be used on them URL: https://theconspiratory.com/theory/ethylene-oxide-sterilised-swabs ## Summary In August 2026 posts began circulating claiming the brush used in a cervical smear test is sterilised in a cancer-causing chemical, and that having the test is therefore dangerous. Full Fact checked it on 17 August. The starting fact is true: ethylene oxide is used to sterilise swabs, speculums and a great deal of other medical equipment, and overexposure to the gas really can cause cancer. The conclusion does not follow, and the people who regulate the devices say so. A spokesperson for the Medicines and Healthcare products Regulatory Agency told Full Fact there is no credible evidence linking the swabs used in cervical smear tests to cancer. Professor Andrea Sella of University College London has described the process as exposing the material to the gas for seconds or minutes and then removing it entirely before packaging, leaving nothing behind. This is not a new claim; the same argument was made about Covid-19 lateral flow tests in 2021 and answered then, including in a Freedom of Information response from the MHRA that is unusually useful to anyone who wants to check for themselves. Keep two things separate: that ethylene oxide is hazardous in occupational quantities, which is documented and uncontested, and the claim this file rates, that a sterilised swab endangers the patient. Nothing here is medical advice. ## The claim That because ethylene oxide is a carcinogen and is used to sterilise medical swabs and brushes, patients undergoing cervical screening or Covid-19 testing are being exposed to a cancer-causing chemical, and the risk is not being disclosed to them. ## Origin and timeline - Long-standing: Ethylene oxide is a colourless gas used around the world to sterilise medical equipment, including swabs, speculums and wound dressings, in cases where heat would damage the item. That it is used this way is not disputed by anyone, including the regulators; the sterilisation method is printed on the packaging. - Also long-standing: Ethylene oxide is genuinely hazardous at sufficient exposure. Too much of it carries health risks including cancer, and severe inhalation can cause lung damage. This is the true premise the claim is built from, and no part of this file disputes it. - 31 March 2021: As lateral flow testing was rolled out to schools and colleges in England, a large number of social media posts warned people not to use the tests because the swabs were sterilised with a cancer-causing chemical. Full Fact checked the claim and rated the tests not unsafe, reporting that ethylene oxide's use in sterilisation does not make the products unsafe, and quoting a Department of Health and Social Care spokesperson. - 28 May 2021: The MHRA published its response to a Freedom of Information request on the safety of ethylene oxide and its use to sterilise lateral flow test swabs, reference FOI-21-294. It sets out the regulatory chain in detail and is the most checkable document in this file. - 2021 to 2022: Variants continued to circulate and were checked individually: that the gas would harm pregnant women given a PCR swab, and that the chemical used to sterilise Covid tests would turn into antifreeze in the body. Full Fact addressed each. The persistence of the argument across several different products is itself part of the pattern. - August 2026: The claim reappeared attached to cervical screening. Posts stating that the brush used in a smear test is sterilised in a cancer-causing chemical, and implying the test is therefore dangerous, were shared hundreds of times across Facebook, Instagram and X. - 17 August 2026: Full Fact published its check. Its verdict is that overexposure to ethylene oxide can be dangerous but that medical devices sterilised with it are not unsafe. An MHRA spokesperson told Full Fact there is no credible evidence that the swabs used in cervical smear tests are associated with cancer, and that negative health effects would involve higher and prolonged exposure. ## The evidence, claim by claim - Claim: Ethylene oxide causes cancer, so a swab sterilised with it exposes patients to a carcinogen. Evidence: The first half is true and the second does not follow from it. Overexposure to ethylene oxide can be carcinogenic and can cause lung damage, which is why exposure is controlled where the gas is handled. What is at issue is whether any of it is still on the device. Professor Andrea Sella, professor of inorganic chemistry at University College London, has described the process as exposing a material to the gas for a few seconds or minutes and then removing the gas entirely before the item is packaged, and said there is nothing left of the ethylene oxide once it is packaged. Dr Alexander Edwards of the University of Reading has told fact checkers that before release from manufacture, a device is checked to ensure no residual ethylene oxide is left. - Claim: Nobody is checking what is left on the device. Evidence: The MHRA's 2021 Freedom of Information response sets out who checks and against what. The manufacturer is responsible for testing residual ethylene oxide on the device to ensure it is below the allowable limit, which is set by the international standard ISO 10993-7:2008. That documentation is reviewed by an independent third-party Approved Body, called a Notified Body in Europe, before the manufacturer may supply the UK market. The Approved Body carries out periodic audits of the manufacturer's process, and the MHRA audits the Approved Bodies. - Claim: There is no way for an ordinary person to verify any of this. Evidence: There is, and it is printed on the box. According to the same MHRA response, swabs may be sterilised using either ethylene oxide or radiation, and the method used is displayed on the packaging: a rectangular box reading STERILE followed by EO for ethylene oxide or R for radiation. The Approved Body responsible carries a unique identifying number shown next to the CE or UKCA mark on the packaging, which can be searched to find that body's name and contact details. A claim that something is being concealed is difficult to sustain about a fact stamped on the wrapper. - Claim: The residue limits are a single number that ignores how the device is used. Evidence: They are not. The MHRA response explains that the permitted residual ethylene oxide on a medical device is set according to how long the device is in contact with the person and what kind of contact it is, with contact time divided into limited, prolonged and permanent categories. A swab used briefly and a device implanted permanently are not held to the same figure. - Claim: This concern is specific to cervical screening. Evidence: The identical argument has been attached to a series of unrelated products since 2021: lateral flow tests, PCR swabs used in pregnancy, and a version claiming the sterilising chemical would turn into antifreeze in the body. Each was checked separately and none held. A claim that transfers cleanly from a nose swab to a pregnancy test to a cervical brush is tracking a manufacturing step, not any particular procedure. ## Why people believe it - The premise is genuinely true, which is what makes it so much stronger than an invented claim. Ethylene oxide really is a carcinogen and really is used to sterilise the swab. Someone who checks that much finds it confirmed and reasonably stops there. - Very few people know that a processing agent is not an ingredient. Sterilisation, like solvent extraction in food manufacturing, is a step that happens to a product and is then reversed out of it, and nothing in ordinary experience teaches that distinction. - The setting raises the stakes. Cervical screening is intimate, uncomfortable and easy to postpone, so a reason to avoid it lands on ground that is already soft, and a warning about a hidden carcinogen is a far more socially acceptable reason to skip an appointment than simply not wanting to go. - The absence of a warning label reads as concealment. Nobody hands you a leaflet about the sterilisation chemistry, so a post that supplies it feels like disclosure of something withheld, when the information was published by the regulator and abbreviated on the packaging. - It has had five years to settle. The argument has been circulating in one form or another since 2021, so many people meeting the smear-test version are recognising something rather than hearing it for the first time, and recognition is persuasive on its own. ## Open questions - How far the August 2026 posts spread beyond the platforms Full Fact names, and whether they have had any measurable effect on cervical screening attendance, is not established in the reporting available here. - Whether the current version originated with a single account or emerged independently from the older lateral flow material is unknown; the claim's structure is identical but no origin has been traced. - The residual limits in ISO 10993-7 have been revised since the 2008 version the MHRA response cites, and which version applies to a given device today is not something this file can establish. ## Latest developments - 2026-08-17T15:45Z: Built on Full Fact's check of 17 August, published as the claim reached cervical screening. Its verdict is that overexposure to ethylene oxide can be dangerous but that medical devices sterilised with it are not unsafe, and an MHRA spokesperson told Full Fact there is no credible evidence that the swabs used in cervical smear tests are associated with cancer. Recorded alongside a note on timing that is not a coincidence of this file's making: the day before, Boatos rated a hoax claiming Oreo filling is made from petroleum derivatives, which runs on the identical error, treating hexane used to extract vegetable oil as though it were in the biscuit. Two claims, two countries, two industries, one confusion between a processing agent and an ingredient. (source: https://fullfact.org/health/brush-cervical-smear-test-no-evidence-cancer-threat/) ## Sources - Smear test brushes are safe, Full Fact (2026): https://fullfact.org/health/brush-cervical-smear-test-no-evidence-cancer-threat/ - Lateral flow tests are not unsafe, Full Fact (2021): https://fullfact.org/online/lateral-flow-tests-ethylene-oxide/ - Freedom of Information request about the safety of ethylene oxide (EO) and its use to sterilize the swabs used in lateral flow tests (FOI-21-294), Medicines and Healthcare products Regulatory Agency (2021): https://www.gov.uk/government/publications/freedom-of-information-responses-from-the-mhra-week-commencing-19-april/freedom-of-information-request-about-the-safety-of-ethylene-oxide-eo-and-its-use-to-sterilize-the-swabs-used-in-lateral-flow-tests-foi-21-294 - Ethylene oxide-sterilised swabs won't cause harm during pregnancy, Full Fact: https://fullfact.org/online/ethylene-oxide-pcr-phe/ - Chemical used to sterilise Covid-19 tests won't turn into deadly antifreeze, Full Fact: https://fullfact.org/health/chemical-used-to-sterilise-covid-19-tests-wont-turn-into-deadly-antifreeze/ - Viral video spreads misinformation about ethylene oxide and Ivermectin, Full Fact: https://fullfact.org/online/ethylene-oxide-covid-test-ivermectin/ - Contrary to claim, Oreo cookies do not contain petroleum derivatives, Boatos.org (2026): https://www.boatos.org/english/are-oreo-cookies-made-with-petroleum-derived-components.html Rated by The Conspiratory, a neutral, sourced encyclopedia of conspiracy theories. Full page: https://theconspiratory.com/theory/ethylene-oxide-sterilised-swabs