I read a bit about drinking diluted chlorine dioxide (e.g. 12mg/L) as a supposedly protective means against COVID-19. Apparently it is a widespread belief in Latin America, especially on social media, that this is a good alternative to getting vaccinated. Here is an article that explores how the usage of ClO2 against COVID-19 became such a widespread practice throughout Latin America: https://osf.io/u9ehf/download.

People who follow this practice support their assertion of efficiency against COVID-19 with articles like the following:

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    At the early part of 2019, chlorine dioxide was also apparently being (stupidly and ineffectively) ingested to cure childhood autism. So the myth goes back to at least before covid. That came from the wikipedia page on chlorine dioxide. I'd like to see more answers focused on this history of this pretend cure. – Jason C Feb 5 at 11:01


Chlorine dioxide is a type of bleach.

The Blue Ridge Poisoning Center at University of Virginia Health put out a specific warning not to drink bleach.

There is a lot of confusing, incomplete, and just plain inaccurate information circulating about how to prevent the COVID-19 virus (“coronavirus”) from spreading. Some advice measures simply won’t help, and some could be downright dangerous. The Blue Ridge Poison Center at UVA Health warns that drinking bleach will not prevent COVID-19 infections and could cause serious injury.

When used correctly, cleaning products can be a safe and effective weapon against the spread of disease-causing germs including the COVID-19 virus (“coronavirus”). In particular, the U.S. Centers for Disease Control and Prevention (CDC) recommends using diluted bleach solutions on frequently-touched surfaces. Hand sanitizer with an alcohol content of at least 60% is recommended for killing COVID-19 on the hands, especially when soap and water is unavailable. However, these products and others used to clean and disinfect may have the potential to be toxic if used incorrectly. Exposure to cleaning products is the second leading cause of calls to poison centers nationwide.

Some cleaning products (including bleach) are caustic, meaning they can cause burns when swallowed or when sprayed or splashed onto the skin or into the eyes.

After Trump suggested injecting disinfectants (dear lord), the CDC had to remind everyone not to do that.

Household cleaners and disinfectants can cause health problems when not used properly. Follow the instructions on the product label to ensure safe and effective use.

In a similar tale, the FDA warned against using the Miracle Mineral Solution which is basically bleach.

Miracle Mineral Solution and similar products are not FDA-approved, and ingesting these products is the same as drinking bleach.

12 mg/L may be hazardous to your health

Very low concentrations can have benefits. It's used as a secondary disinfectant in drinking water. The US EPA puts the maximum safe level in drinking water at 0.8 mg/L.

12 mg/L is well above that and inadvisable.

There is no way to demonstrate it's working, until it doesn't

Outside of a controlled experiment, this treatment will seem to prevent COVID-19 right up to the moment it does not. Meanwhile, it's damaging the body with a caustic substance.

Quackery such as this is not harmless. The health care system does not need another sick person (from long-term chemical poisoning) on their hands. If one truly believes they are immune to COVID they are more likely to put themselves at risk of getting and spreading COVID, especially because may be contagious before they have severe symptoms.

Bleach kills everything, including humans

The papers fall into two categories.

  • bleach against various viruses (not COVID-19) in a lab
  • bleach against various viruses (again, not COVID-19) on humans at safe levels

I'm going to guess folks cherry-picked "bleach is effective against viruses" and "bleach can be used on humans" ignoring the "in a lab" and "at safe levels".

Bleach is very good at killing viruses. This does not mean it only kills viruses. Bleach kills everything, that's why it's so good at disinfecting surfaces. Everything includes humans. We use bleach on humans in very low concentrations because we would like to keep the human alive. Fire is also a pretty good disinfectant, but it is also very harmful to humans. Don't drink fire either.

None of the papers are about drinking unsafe amounts of bleach to cure COVID

None of these papers are about COVID-19. None are about drinking unsafe amounts of bleach. Their only relation is they are about uses of chlorine dioxide, mostly against viruses.

Not a single one is about drinking bleach at 12 mg/L for any reason.

I don't care how bored you are, do not drink bleach.

Before you comment, please keep in mind this is an answer about drinking unsafe amounts of bleach to prevent COVID. It is not a dissertation on the medicinal uses of chlorine dioxide. As such, it is not intended to be technically correct, it is intended to be blunt. Don't drink bleach. It will not prevent COVID.

Nerdy anecdotes such as this one and touch up edits are always welcome.

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    Nitpick: while chlorine dioxide (ClO2) is certainly a type of bleach, it is not the solution that is typically referred to when one says "bleach". The general term "bleach" almost always refers to a dilute solution of sodium hypochlorite (NaOCl). Both ClO2 and NaOCl are bleaching agents, and you are correct from a chemistry perspective when you call ClO2 a "bleach", but the layman will likely be confused. In any case, if confused or unclear, always err on the side of not drinking anything that acts as a bleaching agent. :-) – Cody Gray Feb 4 at 5:23
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    If I read the paper correctly, "Efficacy and Safety Evaluation of a Chlorine Dioxide Solution" concludes (contrary to your literally bold assertions) "a higher safety profile for UC-1 than those yielded in previous studies." Also note that, again contrary to your very bold assertion, household bleach is regularly ingested in a lot of places in the world as a common drinking water disinfectant of the last resort; it is entirely common there and much less harmful than the untreated water. – Peter - Reinstate Monica Feb 4 at 15:20
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    @CodyGray: No one is confused by calling an unknown chemical formula by its household name, pretty much by definition of "household name" (i.e. the commonly understood name). Bleach and bleaching agent are synonymous here. Similarly, "I drove my car into a tree" is clear, and "I drove my GLS into a tree" is less clear for those who are not knowledgeable about types of car. How often I drive a GLS versus my other car is not the point of the story, and the overly pedantic detail detracts from the size of audience the message reaches. – Flater Feb 4 at 16:01
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    @Peter-ReinstateMonica "less unsafe" and "higher safety profile" mean the same thing, I used that phrasing because I didn't want to give any impression the paper was saying its safe to drink bleach. I'm not trying to give the most accurate summary of the papers, I'd really rather not discuss them at all, only enough to show none of them say to drink bleach. As for the EPA regulations, I'd have to run the numbers, but I'm pretty sure it's well below 12mg/L and it does not prevent COVID. – Schwern Feb 4 at 20:08
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    I'm aware the answer is not 100% accurate, it is not supposed to be. Comments which impove the accuracy, like Cody's, are interesting to know. However, when someone is under the delusion that drinking unhealthy amounts of bleach will prevent COVID I prefer to keep the message simple: DO NOT DRINK BLEACH and IT DOES NOT PREVENT COVID – Schwern Feb 4 at 20:14

It may be worth adding that the WHO sets a somewhat higher threshold for toxicity than the EPA, for chlorine dioxide in water, namely 2mg/L.

Anyhow, the problem is that there don't seem to be even animal studies finding that at non-toxic levels (for the host) chlorine dioxide helps with an already established viral infection. So basically there's zero evidence, even from animal studies that it could be a treatment.

Edit: Actually, this is not entirely correct, Peter's answer points to a [not yet formally peer-reviewed/published] preprint of a study in chicken embryos, but it's a bit disconcerting that such a study was only done recently [2020], when chlorine dioxide has been used as a disinfectant for decades. So, you could at least say that for internal use, this is a very experimental treatment, in preclinical stage at best. Also that study noted that "developmental abnormalities were observed in the majority of the infected embryos, including those that received ClO2 treatment", so it seems it's not that foolproof of a treatment, although treatment lowered the servility of some symptoms, including mortality. Viral load was only lowered 2.4-fold in the treatment groups (30-300 ppm ClO2) compared to controls; in absolute terms "average viral load of ClO2-treated chicks was 104.3/mL, range: 103.66 – 105.03 and of untreated chicks was 104.83/mL, range: 104.52 – 105.01, respectively (Tukey HSD, Group E vs. F, p = 0.03)." The study was also limited to a single dose of ClO2, which limited both toxicity [to the host] and effectiveness against the virus. Before any human trials, more complex animal models would have to be tested. E.g. look at how oseltamivir was tested in various animal models; an antiviral like that completely inhibited virus replication in some organs but only partially in other organs in the same animal etc. Chicken embryos are really on the lowest step of the ladder of in vivo (animal) models.

On the interesting, but not-really-relevant side, besides the plethora of studies on chlorine dioxide as an additive in water treatment (remember again, the dose makes the poison) which mostly what the OP linked to, there is also one study on chlorine dioxide killing influenza viruses aerosols. (Again this was at host-safe levels.)

Mice in semi-closed cages were exposed to aerosols of influenza A virus (1 LD50) and ClO2 gas (0.03 p.p.m.) simultaneously for 15 min. Three days after exposure, pulmonary virus titre (TCID50) was 102.6±1.5 in five mice treated with ClO2, whilst it was 106.7±0.2 in five mice that had not been treated (P=0.003). Cumulative mortality after 16 days was 0/10 mice treated with ClO2 and 7/10 mice that had not been treated (P=0.002).

Actually, part of study that strongly indicates that the relevant effect happens outside the body: if application of the ClO2 gas is delayed relative to the virus aerosol, the mice still die aplenty:

When ClO2 gas was delivered 5 min after the delivery of virus aerosols (5 min delay), mortality was 10 % (1/10) (P=0.081 versus no-ClO2 group). The mortality rate was 50 % (5/10) with a 15 min delay, which was [statistically] the same as in animals that received no ClO2 gas treatment.

Thus the ClO2 gas doesn't really treat already infected mice. (It's a bit more complicated why the window is 15 mins, basically the virus has to make its way through mucus etc.)

So, this in aerosol form it could be potentially be a more useful application against a mainly airborne pathogen, but there are substantial practical difficulties putting it in widespread practice since you really need to kill/inactivate the virus before it enters the body with this method/substance.

Additinally, the WHO and the health ministry of Japan have said in a statement that fumigation/spraying devices that are loosely based on that idea (e.g. blow a mist/aerosol of chlorine dioxide in people's faces) aren't approved or effective and that some adverse events have been reported in Japan after exposure to such devices. (There's no technical detail in that newspaper report why the authorities cited say that, but it's probably related to the difficulty of ensuring the (effective but non-toxic) concentration in a larger volume of air from a point source etc.)

Since I see there's some discussion under the other answer about disinfectant mouthwashes... Various kinds of these have been studied with respect to reducing the amount of virus emitted by Covid-19 patients, particularly in a dentistry setting. (There is actually mouhtwash based on chlorine dioxide, although it's not commonly used in dentistry.) But the effect of any such mouthwash products is quite transient, on the order of a few of hours as measured by salivary viral loads (which don't quite drop to zero). Also there has been substantial heterogeneity in the results reported, even for the same active substance; some studies found no reduction, others found a load reduction e.g. in half the patients tested, but not in all of them some reason (which is not really understood). So even for this limited purpose of acting like a "chemical mask" reducing the amount of virus emitted, the evidence regarding disinfectant mouthwashes is mixed.

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    Bleach kills via a chemical reaction, which requires it to come in contact with the target virus. What those studies you cited all show is that once a virus takes root inside your body, there's no feasible delivery mechanism to get the bleach in contact with the virus (at least none that won't kill you for other reasons). Putting bleach into your digestive system to kill something that lives in the respiratory system is certainly pointless. – bta Feb 4 at 17:48
  • Hi @Fizz: I updated the question to remove references to OPs friend, as seeking personal medical advice is off-topic here. You might want to update your answer accordingly (by removing references to OPs friend & passages that read like they are giving personal medical advice - instead of informing about what reliable sources say about the dangers of chlorine dioxide and its (non-)effect on covid). – tim Feb 9 at 8:39

Summary: There is no evidence that ingesting Chlorine Dioxide cures or protects from COVID-19, but the idea is not a priori as patently absurd as it may seem at first glance.

Molecular Chlorine and some chlorine compounds like sodium hypochlorite or chlorine dioxide are known to be effective disinfectants outside of the body. Chlorine dioxide, a water soluble gas, is used in low concentration to treat drinking water. According to the Agency for Toxic Substances and Disease Registry millions of people ingest it every day for this reason.

Inhaling Chlorine dioxide as a gas above safety limits has adverse health effects:

Breathing Chlorine Dioxide can irritate the lungs causing coughing and/or shortness of breath. Higher exposures can cause [...] pulmonary edema

- Chlorine Dioxide Hazrdous Substance Fact Sheet.

This establishes the known frame conditions:

  • Dissolved Chlorine dioxide is effective in deactivating SARs-COV-2 outside of the body.
  • It can be drunk safely in very low concentrations.
  • It has adverse health effects in higher concentrations, particularly when inhaled.

Is it dangerous?

Severe adverse health effects from low concentrations are not to be expected. In other words: Yes, go ahead and drink chlorine dioxide solutions in dilutions below published safety limits if you feel like it. Millions of people do it every day.

However, the reported 12mg/L concentration is an order of magnitude more concentrated than what is considered safe for drinking water by the EPA. Several studies have shown no adverse affects in animals and cell cultures even well above that concentration (e.g. https://res.mdpi.com/d_attachment/ijerph/ijerph-14-00329/article_deploy/ijerph-14-00329.pdf), but there have been reports of life-threatening adverse events, including respiratory and liver failure, at even higher concentrations.

Does it prevent or cure COVID-19?

A possible therapeutic use of chlorine dioxide in low concentrations would not contradict the above facts, but there is no medical evidence that it does.

I could not find a randomized controlled study which showed whether or not it can prevent or cure Covid-19 when ingested. (Obviously though there was not a lot of time to perform one.)

There is a lot of crackpot activity in this field, ranging from irresponsible charlatans to researchers with an agenda1. None of them are robust clinical studies.

But the idea is not a priori as patently absurd as one may think at first glance.

For example, there is a study showing that ClO2 "inhibits the replication of porcine reproductive and respiratory syndrome virus" in cell cultures. Of course, I cannot assess the quality of this study, it does not address SARS-CoV-2, it is ex vivo and it does not seem to be widely cited.

There are a few other, non-peer-reviewed studies performing in vitro or animal experiments.

For example, Evaluation of the antiviral effect of chlorine dioxide (ClO2) using a vertebrate model inoculated with avian coronavirus which showed show that it lowered the viral load of avian coronavirus (IBV, not SARS-CoV2) in tissues of chick embryos.

Our study shows that ClO2 could be a safe and viable way of treating and mitigating the effects of avian coronavirus infections, and raises the possibility that similar effects could be observed in other organisms.

Interestingly, there is a study on mice (https://pubmed.ncbi.nlm.nih.gov/18089729/) that shows how very low-concentrated chlorine dioxide gas in the air mitigates or prevents over-the-air infections with the Influenza A virus. Since the influenza virus has a lipid hull like SARS-CoV-2, low amounts of chlorine dioxide in the air might similarly prevent infection with SARS-CoV-2.

1 E.g. https://www.hilarispublisher.com/open-access/chlorine-dioxide-in-covid19-mechanism-of-molecular-action-in-sarscov2.pdf, whose authors are from the Liechtensteiner Verein für Wissenschaft und Gesundheit which promotes "principles of natural holistic medicine". Never mind holistic approaches to health; they are dearly needed. But unfortunately that label often means "substitute evidence with conviction".

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    @barbecue I was answering the question in the way of skeptics SE (sourced, objective). If you want to apply common sense (i.e. go off topic here): I'm not aware of broken glass having antiviral properties, nor have there been studies showing lower virus load in mice eating glass, nor is there any reason to believe that. – Peter - Reinstate Monica Feb 5 at 2:15
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    "the level for drinking water is safe for large quantities. Since your friend drinks only one liter the overall amount is not far from EPA safe levels" < this part doesn't seem to be coming from the science. Just because it's safe to drink low-level bleach over time, doesn't mean it's also safe to drink high-level bleach over less time followed by no bleach for a while. – Erik Feb 5 at 9:36
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    @ZachLipton I stand by my assessment. All sources I read show that acute toxic effects in rats are only observed at a level of around 20mg/kg body weight; that is 100 times less than what's in the drink /(12 mg total). Also, perhaps surprisingly, household bleach is "fairly benign when ingested". The properties of a ClO2 solution are probably similar, but data is more limited. As to the efficacy: I simply refrained from any speculation. It is not known (but not a priori as insane as it sounds at first). – Peter - Reinstate Monica Feb 5 at 9:39
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    As the FDA link I posted describes, people have suffered "Life-threatening Adverse Events" from drinking chlorine dioxide products while there is simply no meaningful evidence supporting its efficacy for this purpose. I'd imagine those events likely involved higher concentrations, but that illustrates why your answer—which relies on pure speculation for assertions about how much is safe to consume and holding one's nose while doing it—is so dangerous: people who think it's safe can suffer terrible outcomes at the wrong doses. – Zach Lipton Feb 5 at 9:57
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    @Peter-ReinstateMonica You just didn't answer the very simple question the person had. No reputable peer reviewed journal has suggested anything close to "go drink chlorine dioxide" as way to prevent covid. This is skeptics, not an academic discussion. You're answer continues to be dangerous. – jdf Feb 5 at 19:58

Is there any evidence it works?

I have not done extensive reading on this topic, but based on the sources you linked, no, there is no evidence ingesting ClO2 is either preventative or a treatment once infected.

There is very limited evidence that an aerosol of ClO2 may have some protective effect, but the evidence seems to suggest this effect comes from killing the virus in the air before it reaches the victim. The evidence does not support any beneficial effect from a ClO2 aerosol once one is infected.

This paper (from a very crappy journal) gives an overview of some of the evidence. As the authors themselves state:

"Many of these propositions are based on hypotheses, and therefore can only be applied after careful research".

I will also note that the authors are focused on using a ClO2 aerosol as preventative treatment (tenuous but possible) and not ingesting a ClO2 solution.

Is it reasonable to speculate this might work?

While everyone has a different definition of 'reasonable', I would say no, this does not sound feasible.

In order for a disinfectant of this nature to have any effect, it needs to physically reach the virus at a sufficient concentration in order to 'kill' it. The only way for a disinfectant of this nature to reach the virus in an infected individual would be for it to survive their digestive system, enter the bloodstream, and evade filtration by their liver and kidneys. Assuming this is all possible, it then needs to be at a high enough concentration in the blood to kill the virus upon contact. My guess is that at this concentration ClO2 would also start causing lots of other problems including, but not limited to, killing off your own cells.

I am not a doctor or a toxicologist, so this assumption could be incorrect. Without any clinical or experimental data to back up the safety of systemically circulating ClO2 in blood though I think it is best to err on the side of caution.

What this does mean, however, is you would likely need to ingest fairly large quantities of ClO2 in order to achieve the necessary concentration in your blood. (ie 2mg/L ingested <<< 2mg/L in blood, avg. person has ~5L blood) This is likely to exceed current safety limits.

How might I explain this to my friend?

If your friend has a hard time understanding why this isn't feasible you could point to alcohol. Ethanol (the alcohol in beer, wine, and spirits) can kill coronaviruses at a 70% ethanol-to-water concentration (for reference, most spirits such as bourbon and vodka are around 45% ethanol). Despite this, no one is suggesting you drink large quantities of alcohol in order to prevent viral infection. This is because 1) drinking enough to get your blood alcohol concentration even near 55% (the lower bound for efficacy of ethanol as a viral disinfectant) would definitely kill you and 2) heavy alcohol consumption on a regular basis actually suppresses your immune system (for complicated reasons)

While this analogy is far from perfect, it still might be useful in trying to convince the average person why just because something can kill covid in a dish does not mean that ingesting it will be protective or preventative.

So, while ClO2 may kill covid in your drinking water, there is no evidence or reason to believe that drinking such a solution would kill covid in your body, any such claims are purely speculative.

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