Some people blame the preservative thiomersal in vaccines for all kinds of illnesses, but mainly for autism. As thiomersal is a mercury compound, there is some plausibility in suspecting it may cause some damage, but is there some hard data on how dangerous it really is?

How comparable are the effects of thiomersal to equal amounts of elementary mercury or methyl mercury? Is there evidence that the amount that was typically used in vaccines (it is seldom used now) is harmful?

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    It also was used in saline solution for contact-lens wearers quite some time ago. I stopped wearing them in the mid-90s, and my saline had been thimerosal-free for some time. Commented Mar 11, 2011 at 3:09
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    The dose makes the poison. Plenty of things are dangerous if you are exposed to too much (water, for example). The question should be is thiomersal dangerous in the quantities that have been used in vaccines.
    – matt_black
    Commented Sep 19, 2018 at 23:03
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    Haven't they stopped using thiomersal in MMR and other jabs?
    – GordonM
    Commented Sep 20, 2018 at 8:34
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    @GordonM Most of them don't have it anymore. Simple test: If it comes in a single-dose unit there's no thiomersal. If it comes in a vial of many doses there is almost certainly thiomersal. The only reason to put it in is if you're going to use it and then store it for a while. Commented Sep 22, 2018 at 2:11
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    It's quite dangerous--it scares people out of getting vaccinated and thus some die of preventable causes. Commented Oct 13, 2018 at 12:01

3 Answers 3


Thiomersal itself is toxic in quantity, degrading to ethylmercury (C2H5Hg+).

As a vaccine preservative, however, it is harmless. (Global Advisory Committee on Vaccine Safety (2006-07-14): "Thiomersal and vaccines".) This hasn't stopped anti-vaccine activists claiming that the Hg+ atom has nigh-magical powers of autism-causing evil, however, despite no link whatsoever having been found with much research.

  • How does ethyl mercury compare in toxicity to methy mercury? Some anti-vaccine activists use the methyl mercury uptake recommendations to argue against thiomersal, are they comparable in toxicity?
    – Mad Scientist
    Commented Feb 25, 2011 at 0:06
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    The answer is "it doesn't matter, because the quantities in the vaccine are ridiculously tiny by comparison." They are seeing an Hg+, assuming Wakefield wasn't a proven fraud and assuming it must cause autism even if they haven't got a mechanism as yet. Commented Feb 25, 2011 at 0:16
  • Any comment regarding this recent news article? Commented May 26, 2015 at 16:57
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    @user2813274 Yep. Commented Mar 23, 2017 at 3:46

Thimersal does not cause autism. The only study indicating such was proven to be not just shoddy, but an actual fraud committed for the purpose of profiting on the legal fees from ensuing lawsuits. There have been many studies across multiple countries using different vaccine preservatives which show that there's no link between autism and any vaccine.

Thimersal is the poster child for correlation != causation. Just because kids happen to become symptomatic for autism at the same time they get vaccines, people swallowed the bait - hook, line, and sinker.






  • Can you provide links to the fraud finding?
    – morganpdx
    Commented Feb 24, 2011 at 23:55
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    @morganpdx Russel is certainly refering to Andrew Wakefield, see this link for some information on that: scienceblogs.com/insolence/2011/01/… . Brian Deer has written a lot about that case, if you're interested.
    – Mad Scientist
    Commented Feb 24, 2011 at 23:58
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    Godlee F., Smith J., Marcovitch H. "Wakefield’s article linking MMR vaccine and autism was fraudulent." BMJ 2011; 342:c7452 doi: 10.1136/bmj.c7452 (Published 5 January 2011) bmj.com/content/342/bmj.c7452.full Commented Feb 24, 2011 at 23:59
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    Actually, that's not correlation != causation, because there isn't even a correlation. What we have here is observation bias, where people who's kids coincidentally became symptomatic after vaccines assume correlation, because they're not looking at the vast number of kids where it didn't happen. When you vaccinate a million kids a year, some of them will have diseases or conditions manifest at nearly the same time. Commented Jul 14, 2011 at 19:36

Thiomersal is toxic, in much higher dosages than found in vaccines.

Here is some safety information about thiomersal.

Its OEL (occupational exposure limit) is 0.05 mg/m3. (Ibid)

[And the autism link, is of course, fraudulent nonsense.]


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