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There is a common pro-vaccination argument that attempts to equate the amount of formaldehyde injected into the body when receiving a vaccine, with the amount of formaldehyde ingested into the GI tract when eating a pear.

Here is a classic example:

  • Refutations to Anti-Vaccine Memes

    120 times

    A 200g pear contains up to 12,000 μg of formaldehyde naturally.

    Vaccines contain up to 100 μg, or 0.83% of the formaldehyde in a pear.

    i.e. A pear contains 120 times more formaldehyde than a vaccine.

I loathe this argument mainly as a non-sequitur factoid, but also because it is often parroted without references in a hypocritical argument to tell people not to believe everything they are told.

For example, it is not hard to find (repeated) examples of similar claims with different numbers:

  • Science Alert: Six myths about vaccination – and why they’re wrong

    there’s 600 times more formaldehyde in a pear than a vaccine.

  • Just the Vax: The Toxin Gambit Part 1: Formaldehyde

    Put another way, the amount contained within a vaccine is more than 50 times less than what is in a pear.

  • I found this image on a Mothering.com forum

    600 times image

    The difference is subtle, but notice it is 600 times as much (a factor of 5 increase), and the level of blue has changed by maybe 10%.

  • Vaxplanations repeat the 120 times claim, but I give them credit for also addressing the ingestion versus injection difference.

  • Gizmodo says a 220 g pear contains 8,600 to 13,200 µg of formaldehyde, putting the original 12,000 µg for a 200 g pear at the upper end.

  • This forum commenter seems to have lost a percentage sign:

    A typical vaccine may contain up to 100 ug, or 0.83 of the formaldehyde available in a typical pear.

So what is the real ratio of formaldehyde between a typical pear and a typical vaccine? 50:1, 120:1, 600:1, 1:0.83 or a different number?

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    The dose makes the poison. Does either side of the argument even address the formaldehyde dose that would matter to a human baby (in comparison to how much vaccine or pear contains)? – user5341 Apr 19 '16 at 16:47
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    From a link in DavePhD's answer: "Formaldehyde is essential in human metabolism and is required for the synthesis of DNA and amino acids (the building blocks of protein). Therefore, all humans have detectable quantities of natural formaldehyde in their circulation (about 2.5 ug of formaldehyde per ml of blood). Assuming an average weight of a 2-month-old of 5 kg and an average blood volume of 85 ml per kg, the total quantity of formaldehyde found in an infant's circulation would be about 1.1 mg, a value at least five times more than the amount an infant would be exposed to in vaccines." – JasonR Apr 19 '16 at 16:58
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    Note that vaccines are not injected into the bloodstream but rather into the muscle. – James McLeod Apr 19 '16 at 19:38
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    @JasonR So, basically, eating a pear gives you ten times as much formaldehyde as eating a baby. It seems that the pear lobby is suppressing this important dietary information. – David Richerby Apr 19 '16 at 21:34
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    This comparison would only make sense if one could inject himself with a pear. – Dmitry Grigoryev Apr 20 '16 at 11:13
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No. The amount of formaldehyde in 200 grams of pear is about 7 times the maximum that an infant would receive from a single vaccine, as explained below:

According to Determination of formaldehyde in foods, biological media and technological materials by headspace gas chromatography Chromatographia December 1996, Volume 43, pages 625-627:

Sample: Pears

Formaldehyde content: 7.4 mg/kg

Number of samples: 18

Given 200 grams of pear, 7.4 mg/kg corresponds to 1.48 mg (1480 μg) of formaldehyde

According to Children's Hospital of Philidelphia's page Vaccine Ingredients – Formaldehyde

The average quantity of formaldehyde to which a young infant could be exposed at one time may be as high as 0.2 mg

It lists the formaldehyde concentrations (or upper limits) of various vaccines. It lists Japanese encephalitis vaccine as having up to 0.2 mg (200 μg) of formaldehyde.

So the proper ratio is 1480:200 or 7.4:1.

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    According to this document: cfs.gov.hk/english/whatsnew/whatsnew_fa/files/formaldehyde.pdf a pear can have 38.7-60 mg/kg. They say this is from WHO. Those levels are almost a factor of 10 higher than your answer quotes. – JasonR Apr 19 '16 at 17:03
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    Pear does not contain as much formaldehyde as meme says, but still vastly more than a vaccine. So meme is correct, just numbers are bit off. – Peter M. Apr 19 '16 at 18:03
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    The first line should be changed to "No (but it still contains more, just not by that margin)" or something similar, for the sake of future readers who might only give a casual glance. Otherwise this answer could be misinterpreted by an anti-vaccination advocate as "look, the answers was a clear NO, so the claim that pears contain more formaldehyde was a silly lie, pears contain much less than vaccines". – vsz Apr 19 '16 at 23:16
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    If a pear contains 7 times the amount in a vaccine, that means that it contains 600% more formaldehyde than a vaccine contains. Perhaps someone confused 600% more with 600 times. – Matt Malone Apr 20 '16 at 13:24
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    @fredsbend formaldehye is a very simply molecule, there is only one formaldehyde, no matter the source. – Mad Scientist Apr 21 '16 at 11:56
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No, the maths on these memes don't quite add up, but it is fair to say that a pear does still contain quite a bit more formaldehyde than any vaccine by at least a factor of 10.

According to the WHO (World Health Organization), (PDF File) a Pear can contain 6 to 38.7 mg/kg of formaldehyde. That would mean for a 200 gram pear, we have anywhere from 1.2 to 7.74 mg.(1)

According to the Children's Hospital of Philadelphia, the vaccine with the highest amount of formaldehyde is the Japanese Encephalitis vaccine at a whopping 0.2mg. However, that vaccine is not on the standard CDC schedule (PDF File). The highest amount in a regularly scheduled vaccine is actually 0.1mg.

So at a worst case scenario for a regularly scheduled vaccine, a 200g pear may have 77 times the formaldehyde that type of a vaccine. At best, we are talking 12 times the amount. So pear is greater than vaccine. However, that doesn't really matter.

This is all a non-sequitur argument as Oddthinking points out (injection versus ingestion for instance). I think the really important point comes from the Children's Hospital website (emphasis mine):

Formaldehyde is essential in human metabolism and is required for the synthesis of DNA and amino acids (the building blocks of protein). Therefore, all humans have detectable quantities of natural formaldehyde in their circulation (about 2.5 ug of formaldehyde per ml of blood). Assuming an average weight of a 2-month-old of 5 kg and an average blood volume of 85 ml per kg, the total quantity of formaldehyde found in an infant's circulation would be about 1.1 mg, a value at least five times more than the amount an infant would be exposed to in vaccines.

That right there should put a nail in the coffin of that bad argument. As a human adult, you will have 4.5 to 5.5 liters of blood. This means you have 11.25 to 13.75 mg of formaldehyde in your body anyway (maths in comments below didn't scale properly apparently).


(1) - Please note, there does seem to be a systematic typo that exists in the documentation. The original German document lists 6 - 38.7 mg/kg. This figure has been turned into 38.7 - 60 mg/kg. For the purposes of this answer, I am using the original citation of MÖHLER, K. & DENBSKY, G. (1970) [Determination of formaldehyde in foods.] Z. Lebensm. Unters. Forsch., 142: 109-120.

NOTE: With the above referenced typo, the first meme would be considered mostly correct (i.e. 60 mg/kg does indeed give an answer of 12,000 micrograms, or 12mg as an answer at the upper end. So while not 600 times, the 120 times is an understandable mistake). Another mistake is that 7 times anything is about 600%, so a percent symbol getting dropped could be another cause of that confusion. This is all "below the line" speculation though, as tracing the origins of mistakes is probably beyond the scope of this site.

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    Just because I have 5×x of a substance in my body does not mean that ingesting me with a quantity of 1×x is harmless. Suppose I have 40 litre water in my body. If I am suddenly ingested with 8 litre, I would be not happy. I don't dispute that ingestion of a small amount of formaldehyde is safe, but the fact that we have a 5× larger quantity in our body already is not itself sufficient evidence to support that. – gerrit Apr 19 '16 at 17:39
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    @gerrit, the word you're looking for in this case is injected or inject, "ingesting me" implies that someone is eating you. However I agree with your overall argument. – Ryan Apr 19 '16 at 17:50
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    I would indeed be interested in the injection vs ingestion difference, with injection, it all ends up in the bloodstream, whereas with ingestion a significant portion might be degraded or not absorbed. In the absence of measure about how much formaldehyde from a pear makes into the bloodstream when eating said pear, this is all pretty inconclusive. – Matthieu M. Apr 19 '16 at 17:52
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    @pydsigner I would say it's irrelevant since it's comparing "apples to pears" as it were. :) – JasonR Apr 19 '16 at 19:18
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    @MatthieuM. Yeah, definitely. The "natural blood content" (and natural in-body production) is a much better argument ceteris paribus. But, well, it's most likely a counter-argument to an even more ridiculous claim. I'm guessing the guys using formaldehyde content as an argument against vaccination have no idea how formaldehyde works in the body, how it is produced and that quite a bit of it is produced whenever you drink alcohol, for example. This kind of meme is targeted precisely on people like that - thinking that formaldehyde is un-natural or that natural means desirable or healthy. – Luaan Apr 20 '16 at 8:37

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