Do you need to worry about thimerosal in vaccines?

Way back before the 1930’s lots of kids were dying from vaccine-related bacterial infections. That’s because kids were given their vaccines from multi-dose vials–vials intended to be used more than one time, but with different needles.

It turns out that’s not a very clean way of giving vaccines.

This allowed for bacteria and fungi to grow inside the vials. Then, the microorganisms would get injected into the bodies of the kids that came after the first injection. However, that changed with the addition of preservatives in vaccines. 

Preservatives are used in vaccines to prevent or kill any growth of bacteria, fungi, or other microorganisms that might have contaminated the vaccine vial.

Due to tragic events in history, such as the infection of children with deadly bacteria after injection with multi-dose vaccines, the United States Code of Federal Regulations (the CFR) required preservatives to be added to multi-dose vials of vaccines. 

Preservatives have been required in multi-dose vaccines since the 1930s.

Since then, thimerosal has been the most widely used preservative in multi-dose vaccines. It has a long record of safety and has been proven effective at preventing bacterial and fungal contamination of vaccines. However, over the past several years, thimerosal has become a target for controversy due to its mercury concentration and concern for safety.

Let’s talk thimerosal:

Yes, thimerosal contains mercury. It is about 50% mercury by weight. A vaccine composed of 0.01% thimerosal as a preservative contains approximately 25 micrograms of mercury per 0.5 mL dose.1

Mercury is an element that is found as inorganic mercury salt in the water, soil, plants, and animals. It occurs naturally in the Earth’s crust, air, soil, and water. Since the beginning of time, occurrences such as volcanic eruptions, rock weathering, and coal-burning have all contributed to the release of mercury into the environment. The mercury in the environment then gets changed by certain types of bacteria into a compound called methyl mercury. Methyl mercury accumulates in the aquatic food chain an organic form and can land in larger quantities on your plate in seafood. These organic forms of mercury are more easily absorbed and harder to eliminate from the body when ingested.

At high levels, methyl mercury can be toxic to people. Methyl mercury is a neurotoxin and not the form of mercury found in thimerosal. The consumption of this form of mercury, such as through eating contaminated fish or exposure to methyl mercury fungicide, for example, has been associated with physical side effects. Many studies have been conducted on methyl mercury, of which the mercury health guidelines have been established.

But not all forms of mercury are the same.

Thimerosal is a derivative of ethyl mercury. This tiny change in wordage relates to a hugely different toxicological profile. Studies comparing methyl and ethyl mercury suggest that these two types of mercury are processed differently in the body.Ethyl mercury has been shown to break down by the body and get excreted much more rapidly than methyl mercury, and therefore is much less likely to accumulate in the body and cause harm.

Thimerosal Toxicity:

Allergic reactions to thimerosal have been described in the clinical setting.1 Most of the reactions seen have been delayed hypersensitivity reactions such as redness and swelling at the injection site.4,5 The reactions tend to be mild and last only up to a few days. However, when an allergic reaction is seen in the clinical setting, it’s nearly impossible to tell whether the reaction was due to the thimerosal or to another component of the vaccine.1

One study published in 1931 involved the injection of a 1% thimerosal solution into subjects, with no reported side effects except for 2 cases of skin sloughing.6 As stated before, the thimerosal component in vaccines currently is 0.01%, ten-fold lower than the concentration used in this study.

Another study conducted in 1985 compared the toxicity of ethyl and methyl mercury in adult rats. After feeding the rats the mercury concentrations daily, the study found that the ethyl mercury, the mercury found in thimerosal, to be less neurotoxic than the methyl mercury.Still, guidelines for mercury safety are based on methyl mercury.

Finally, a study conducted in 2002 may be of the most importance. Due to the concern that infants may lack the ability to eliminate the mercury in vaccines, a study conducted at the University of Rochester and National Naval Medical Center in Bethesda, MD looked at the levels of mercury in the blood and other samples from infants who had received routine vaccinations containing thimerosal. They found that in every infant included in the stud,y the levels of mercury in the blood samples didn’t exceed the methyl mercury safety guidelines.8 Also, they found that mercury was cleared from the infants’ blood faster than predicted for methyl mercury and that most of the mercury was excreted in the stool fairly quickly.8

The study suggests that thimerosal is removed much more rapidly from the body than methyl mercury. Currently, follow-up studies are being conducted, paid for by the National Institute of Allergy and Infectious Diseases (NIAID).

Thimerosal and neurodevelopmental disorders, such as autism:

Many studies have shown that there is no association between thimerosal exposure and autism.

For a list of studies on thimerosal and autism, check out the Children’s Hospital of Philadelphia (CHOP) website.

In 2001, the Institute of Medicine (IOM) convened a committee to discuss and review vaccine safety-related issues. One review focused on the potential relationship between thimerosal in vaccines and neurodevelopmental disorders. They concluded that the evidence that thimerosal caused autism, attention deficit hyperactivity disorder (ADHD), and speech or language delay was not great enough to link the two.9

In 2004 the IOM issued its final report on thimerosal and autism. The committee concluded that there is no causal relationship between thimerosal-containing vaccines and autism.1 Also, they stated that the benefits of vaccination are tried and true and that “the hypothesis of susceptible populations is presently speculative, and that widespread rejection of vaccines would lead to increases in incidences of serious infectious diseases like measles, whooping cough and Hib bacterial meningitis”.1

However, the IOM committee decided that the removal of thimerosal from vaccines was “a prudent measure in support of the public health goal to reduce mercury exposure of infants and children as much as possible”.1

So, is thimerosal safe?

The three U.S. health agencies, The Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), and the National Institutes of Health (NIH), have looked at all of the current research on thimerosal and have found it to be safe to use in vaccines.3

Also, the organizations, The National Academy of Sciences’ Institute of Medicine, the Advisory Committee on Immunization Practices (ACIP), and the American Academy of Pediatrics (AAP) have found thimerosal to be safe after reviewing the research.3

What vaccines still contain thimerosal?

The great news is that all of the childhood vaccines are thimerosal-free! So you don’t need to worry about it any longer! 

Some of the influenza vaccines are produced in multi-dose vials, and therefore contain thimerosal.  You can always ask for a thimerosal-free flu vaccine.

Several other vaccines do contain thimerosal. For a complete list of the vaccines containing thimerosal: HERE.

*Note: Vaccines that are considered trace-thimerosal-containing formulations have 1 microgram or less of mercury per dose. Full thimerosal vaccines have around 25 micrograms per dose, with the exception of inactivated influenza vaccine. 


  1. U.S. Food and Drug Administration (FDA). Department of Health and Human Services.
  2. Vaccine Education Center at The Children’s Hospital of Philadelphia (CHOP).
  3. The Centers for Disease Control and Prevention (CDC).
  4. Cox NH, Forsyth A. Thimerosal allergy and vaccination reactions. Contact Dermatitis 1988;18:229-233.
  5. Grabenstein JD. Immunologic necessities: diluents, adjuvants, and excipients. Hosp Pharm 1996; 31:1387-1401.
  6. Powell HM, Jamieson WA. Merthiolate as a Germicide. Am J Hyg 1931;13:296-310.
  7. Magos L, Brown AW, Sparrow S, Bailey E, Snowden RT, Skipp WR. The comparative toxicology of ethyl- and methylmercury. Arch Toxicol 1985,57:260-267.
  8. Pichichero ME et al. Mercury levels in premature and low birth weight newborn infants after receipt of thimerosal-containing vaccines. J Pediatr. 2009 Oct;155(4):495-9. Epub 2009 Jun 26.
  9. IOM (Institute of Medicine). Thimerosal-containing vaccines and neurodevelopmental disorders. Washington DC: National Academy Press; 2001.

11 thoughts on “Do you need to worry about thimerosal in vaccines?”

  1. Thanks for reading. I feel that I have made sure to list the reactions associated with each vaccine outlined in my posts. Extreme reactions to vaccines are rare, as I have stated in each entry, however they can happen. I think this is something the readers understand from reading these posts. Vaccines can have side effects.

  2. Dr. Heath Motley

    Here are some great links you might like too. Or for any nea sayers.

    Please stop telling people vaccine injuries are rare and brushing off individuals who have suffered vaccine injuries. Vaccines are associated with serious adverse reactions like: Blood and lymphatic system disorders, immune system disorders, myocarditis, nervous system disorders, convulsions, seizures, encephalitis (brain swelling), facial palsy, skin disorders, sudden infant death (SIDS), death, meningitis, paralysis, anaphylactic shock, skin and tissue disorders, eczema, lower respiratory infections, cerebrovascular accident, transverse myelitis, Guillain-Barré syndrome, Bell’s palsy, aseptic meningitis, pneumonia, ringing in the ears, multiple sclerosis, myelitis including transverse myelitis, seizure, febrile seizure, peripheral neuropathy, herpes zoster, migraines, neurological syndromes, chronic arthritis, hearing loss, rheumatoid arthritis, vasculitis, neuropathy, and vaccine-strain versions of chicken pox, measles, mumps, polio, influenza, meningitis, yellow fever, and pertussis.

    For a list of other exciting (yet downplayed) reactions check out the package inserts here.

    To view the VAERS database where you will find more adverse reactions reported including deaths, click here.

    Vaccines cause Chromosome Changes Leading to Mutations, Leukemias and Lymphomas, Auto-immunity, Diabetes, Nervous System Changes, Autism, Demyelination, Seizures, Convulsions, Epilepsy, Brain Swelling, Unexplained Diseases, Another Vaccinal Disease like Paralytic Poliomyelitis, tentanus, smallpox, etc. Following Inoculation, Death of course, metabolic problems, deafness, kidney disorders, skin disorders, abcesses, shock and more.

    Health Guide: Vaccine Research

    Vaccine References

    my list of peer reviewed vaccine research

    Keep in mind that it is mainly doctors and researchers who are anti-vaccine, even the CDC admitted that anti-vaxxers are on average far more educated than pro-vaxxers. This is why the anti-vaxxers are always posting science while the pro-vaxxers are throwing insults.
    Vaccine Facts backed by Science!vaccine-faqs/c1swe

    WE WANT THE FACTS!the-factsscience/cc2d

    Research supporting Vaccine/Autism Causation
    Evidence for Thimerosal Risk – Page 1

    Evidence for Thimerosal Risk – Page 2

    Vaccine Ingredients — A Comprehensive Guide
    Adverse Effects of Adjuvants in Vaccines

    87 Published Works on Vaccines and Adverse Health Concerns

    Vaccine Ingredients

    Vaccines Additives

    Papers Showing a Connection Between Thimerosal Exposure and Neurological Harm

    What we’re all tired of is people pretending the American Medical Association has been around since the beginning of time and that everything else is “new age, pseudoscience, and conspiracy theory.” I hate to point out the obvious but the AMA has only been around since 1847. Before that, there were homeopathic physicians/doctors (1789) homeopathic hospitals (1825), and the establishment of the American Institute of Homeopathy in (1841). To say medicine has had a horrible track record.
    Big Pharma Horror Stories
    A long list of disaster stories.

    If anything sounds like a “conspiracy theory” it’s the belief that the immune system requires the administration of a germ to protect itself from a germ.
    Learn more about the harm vaccine do:
    Vaccines and Brain Inflammation

    Vaccines Did Not Save Us – 2 Centuries Of Official Statistics

    Why Vaccination Continues even though it is dangerous and ineffective

    Fact, vaccines have never eradicated anything, ever

    Smoke, Mirrors, and the “Disappearance” Of Polio

    Did Vaccines Really Eradicate Polio? by Suzanne Humphries, MD

  3. Thimerosal Inhibits Dendritic Cell Function by Oxidizing Sulphydril Groups
    Department of Immunology; University of California, Irvine; Irvine, California.

    Results: The results of this study demonstrated that: 1) Thimerosal impairs human monocyte derived dendritic cell function and is cytotoxic at high doses 2) Thimerosal treated DCs were inefficient at priming T cells 3) Addition of thiol containing compound Glutathione restores dendritic cell function and viability.

    Conclusions: Exposure to thimerosal significantly affected the maturation of DCs. Lower doses lead to reduction in pro-inflammatory cytokine secretion and up-regulation of co-stimulatory molecules while it was cytotoxic at higher doses inducing apoptosis in DCs. However, the secretion of anti-inflammatory cytokine, IL-10, by DCs was not affected by thimerosal because it is involved in suppressing T cell proliferation. Mercury and other heavy metals are well known to increase oxidative stress and deplete intracellular glutathione. Here we show that the depletion of glutathione or thiol groups by thimerosal to be the major mechanism responsible for affecting DC function and cytotoxicity. Alterations in immune function through depletion of GSH in DCs may play a key role in exacerbating autoimmune and allergic responses associated with use of thimerosal.

    Toxicol Sci. 2005 Jul;86(1):132-40. Epub 2005 Apr 20.
    Effects of thimerosal on NGF signal transduction and cell death in neuroblastoma cells.
    Parran DK, Barker A, Ehrich M.
    Virginia-Maryland Regional College of Veterinary Medicine, Laboratory for Neurotoxicity Studies, Virginia Tech, 1 Duckpond Drive, Blacksburg, Virginia 24061-0442, USA.
    Signaling through neurotrophic receptors is necessary for differentiation and survival of the developing nervous system. The present study examined the effects of the organic mercury compound thimerosal on nerve growth factor signal transduction and cell death in a human neuroblastoma cell line (SH-SY5Y cells). Following exposure to 100 ng/ml NGF and increasing concentrations of thimerosal (1 nM-10 microM), we measured the activation of TrkA, MAPK, and PKC-delta. In controls, the activation of TrkA MAPK and PKC-delta peaked after 5 min of exposure to NGF and then decreased but was still detectable at 60 min. Concurrent exposure to increasing concentrations of thimerosal and NGF for 5 min resulted in a concentration-dependent decrease in TrkA and MAPK phosphorylation, which was evident at 50 nM for TrkA and 100 nM for MAPK. Cell viability was assessed by the LDH assay. Following 24-h exposure to increasing concentrations of thimerosal, the EC50 for cell death in the presence or absence of NGF was 596 nM and 38.7 nM, respectively. Following 48-h exposure to increasing concentrations of thimerosal, the EC50 for cell death in the presence and absence of NGF was 105 nM and 4.35 nM, respectively. This suggests that NGF provides protection against thimerosal cytotoxicity. To determine if apoptotic versus necrotic cell death was occurring, oligonucleosomal fragmented DNA was quantified by ELISA. Control levels of fragmented DNA were similar in both the presence and absence of NGF. With and without NGF, thimerosal caused elevated levels of fragmented DNA appearing at 0.01 microM (apoptosis) to decrease at concentrations >1 microM (necrosis). These data demonstrate that thimerosal could alter NGF-induced signaling in neurotrophin-treated cells at concentrations lower than those responsible for cell death.

  4. Here is a study showing that very tiny amounts of thimerosal affect dendritic cells, which “are potent antigen-presenting cells that initiate primary immune responses.”

    Uncoupling of ATP-mediated calcium signaling and dysregulated interleukin-6 secretion in dendritic cells by nanomolar thimerosal.
    Article about this study:
    “The slightest fluctuation in how calcium channels ‘communicate’ can alter the growth, maturation and activation of dendritic cells,” explained [Dr. Isaac] Pessah. “Thimerosal dramatically alters how two key calcium channels, code-named RyR1 and IP3R1, found in dendritic cells function as a team by ‘garbling’ the normal signaling system between them.”
    When thimerosal, at a concentration as low as 20 parts per billion, alters the fidelity of normal calcium signals, dendritic cells show abnormal secretion of IL-6 cytokine – a potent chemical signal that initiates inflammatory responses. Higher concentrations – 200 parts per billion – causes programmed death of dendritic cells, preventing them from maturing and doing their primary job of activating T-cells. Without proper feedback to guide its response, a normal dendritic cell can quickly become “a rogue, producing misinformation that could activate aberrant and harmful immune responses,” Pessah explained. “Even one rogue dendritic cell can activate many inappropriate immune responses.”
    The actual study:

  5. Here is a study comparing ethyl and methyl mercury toxicology:

    Arch Toxicol. 1985 Sep;57(4):260-7.
    The comparative toxicology of ethyl- and methylmercury.
    Magos L, Brown AW, Sparrow S, Bailey E, Snowden RT, Skipp WR.
    Neurotoxicity and renotoxicity were compared in rats given by gastric gavage five daily doses of 8.0 mg Hg/kg methyl- or ethylmercuric chloride or 9.6 mg Hg/kg ethylmercuric chloride. Three or 10 days after the last treatment day rats treated with either 8.0 or 9.6 mg Hg/kg ethylmercury had higher total or organic mercury concentrations in blood and lower concentrations in kidneys and brain than methylmercury-treated rats. In each of these tissues the inorganic mercury concentration was higher after ethyl- than after methylmercury. Weight loss relative to the expected body weight and renal damage was higher in ethylmercury-treated rats than in rats given equimolar doses of methylmercury. These effects became more severe when the dose of ethylmercury was increased by 20%. Thus in renotoxicity the renal concentration of inorganic mercury seems to be more important than the concentration of organic or total mercury. In methylmercury-treated rats damage and inorganic mercury deposits were restricted to the P2 region of the proximal tubules, while in ethylmercury-treated rats the distribution of mercury and damage was more widespread. There was little difference in the neurotoxicities of methylmercury and ethylmercury when effects on the dorsal root ganglia or coordination disorders were compared. Based on both criteria, an equimolar dose of ethylmercury was less neurotoxic than methylmercury, but a 20% increase in the dose of ethylmercury was enough to raise the sum of coordination disorder scores slightly and ganglion damage significantly above those in methylmercury-treated rats.

  6. Effect of thimerosal, methylmercury, and mercuric chloride in Jurkat T Cell Line
    Gianpaolo Guzzi, Paolo D. Pigatto, […], and Caterina A.M. La Porta
    Interdiscip Toxicol. 2012 September; 5(3): 159–161
    “the treatment of Jurkat T cells with thimerosal caused a significant decrease in cellular viability at 1μM (25%, p<0.05; IC50: 10μM). Methyl mercury exhibited a significant decrease in cellular viability at 50μM (33%, p<0.01; IC50: 65μM)… Our findings demonstrate that thimerosal at the concentration usually found in vaccines, affects significantly cellular viability…”!po=50.0000

    Here is a paper describing poisoning by ethyl mercury fungicides on seeds which were used to make bread. Of course the type of exposure (ingestion) was different, and the amount of mercury much higher than what is used in some vaccines.

    Poisoning By Ethyl Mercury Toluene Sulphonanilide
    "Many systems were involved, including the kidneys, the gastro-intestinal tract, the skin, the heart, and the muscles, but involvement of the nervous system was the most constant with disturbance of speech, cerebellar ataxia, and spasticity. Mental abnormalities were occasionally observed. Many patients died."

    Accidental ethyl mercury poisoning with nervous system, skeletal muscle, and myocardium injury.
    “Four case reports are presented of patients who ate the meat of a hog inadvertently fed seed treated with fungicides containing ethyl mercury chloride. The clinical, electrophysiological, and toxicological, and in two of the patients the pathological data, showed that this organic mercury compound has a very high toxicity not only for the brain, but also for the spinal motoneurones, peripheral nerves, skeletal muscles, and myocardium.”

  7. Here is a very evenhanded comparison of the toxicity of methyl mercury in fish, ethyl mercury (thimerosal) in vaccines, and mercury vapors from amalgam tooth
    The author states that there is a paucity of research on the toxicity of ethyl mercury, but also cites evidence indicating that thimerosal can be very toxic.
    “Ethyl mercury in the form of thimerosal has found wide application in medicine as a disinfectant. Axton (54) reported case histories of four children and two adults severely poisoned by accidental exposure. Five of the six cases died. Rohyans et al. (55) reported a case of severe poisoning from treatment of an infected ear. Pfab et al. (56) reported on an attempted suicide from drinking a solution of thimerosal, resulting in severe poisoning. Treatment of infants with omphaloceles resulted in high levels of mercury in autopsy tissues (57). Cases of human poisoning have also occurred from infusion of large volumes of plasma containing thimerosal as a preservative (58,59).”
    54. Axton JHM.
    Six cases of poisoning after a parenteral organic mercurial compound (Merthiolate). Postgrad Med J 48:417–421 (1972).

    55. Rohyans J, Walson PD, Wood GA. MacDonald WA.
    Mercury toxicity following Merthiolate ear irrigations.
    J Pediatr 104:311–313 (1984).

    56. Pfab R, Muckter H, Roider G, Zilker T.
    Clinical course of severe poisoning with thimerosal.
    Clin Toxicol 34:453–460 (1996).

    57. Fagan DG, Pritchard JS, Clarkson TW, Greenwood MR.
    Organ mercury levels in infants with omphaloceles treated with organic mercurial antiseptic. Arch Dis Child 52:962–964 (1977).
    “Samples of fresh and fixed tissues from infants with exomphalos treated by thiomersal application were analysed for mercury content. The results showed that thiomersal can induce blood and organ levels of organic mercury which are well in excess of the minimum toxic level in adults and fetuses.”
    These infants died afte their umbilical cords were painted with merthiolate.

    58. Suzuki T, Takemoto T-I, Kashiwazaki H, Miyama T.
    Metabolic fate of ethylmercury salts in man and animal. In: Mercury, Mercurials and Mercaptans (Miller MW, Clarkson TW, eds). Springfield, IL:Charles C. Thomas, 1973;209–232.

    59. Matheson DS, Clarkson TW, Gelfand EW. Mercury toxicity (acrodynia) induced by long-term injection of gamma globulin. J Pediatr 97:153–155 (1980).

Comments are closed.

Scroll to Top