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Vaccine Ingredients

Vaccine ingredients can be confusing. They are often 6-syllable words that are totally foreign to most parents. We’re here to help. In this section we break down the common types of ingredients in vaccines. 


And antigen is a foreign substance (e.g., bacterium or virus) capable of causing an immune response in the body. The presence of antigens in the body triggers the immune system to act, usually producing antibodies and other immune cells.

In a vaccine, the antigen helps your body recognize a disease so your immune system can fight it. Because an antigen is modified, it cannot cause the disease. Common ways that antigens are modified include:

  • Using only a piece not the whole virus or bacteria
  • Killing the virus or bacteria
  • Weakening the virus or bacteria so much that it cannot make you sick
  • If you think of a disease like a robber that is wearing a red coat, an antigen is the red coat – it helps identify the disease but isn’t dangerous itself.

Understanding Formaldehyde in Vaccines

Formaldehyde has been used in some vaccines for many years to inactivate viruses or detoxify bacteria so the vaccines don’t cause sickness. If you’re not an organic chemistry expert that can sound scary but here are the facts:

  • Formaldehyde is actually naturally in our bodies, it’s vital for our metabolic process.
  • Like everything, it is how much formaldehyde in your body that determines if it is dangerous.
  • Vaccines have an extremely small amount of formaldehyde. The highest amount found in a dose of vaccine is 0.02 mg but a newborn will have about 50 times that naturally in their body.

Don’t fall prey to disinformation. Learn the facts in order to protect your family. Learn more at:


Adjuvants are “booster” ingredients – they help your body produce a stronger immune response which means greater protection against a disease. An interesting trivia fact is that the word adjuvant comes from the Latin “adjuvare” which means to help or aid, which is exactly what an adjuvant does. The advantage of adjuvants is that they help produce more antibodies and longer-lasting immunity so a smaller amount of the virus or bacteria needs to be used in the vaccine.

Adjuvants have been used in vaccines since the 1930s. Millions of American children have safely received vaccines with adjuvants for decades. Like all vaccines, adjuvanted vaccines are rigorously tested in clinical trials to ensure they are both safe and effective. Once they are approved in the U.S. adjuvanted vaccines continue to be monitored by the CDC and FDA.

A commonly found adjuvant is aluminum which has concerned some parents. Here are the facts:

  • Aluminum is naturally found in fruits, vegetables, meats, and fish – that’s because it’s the 3rd most abundant element on earth.
  • The amount of aluminum found in vaccines is well within safe limits. For example, the amount of aluminum infants receive from vaccines in their first 6 months is about 4.4 mg. During the same six months, a breast-fed baby will typically receive more than twice the amount in a vaccine from their mother’s milk.

Learn more about adjuvants:


Sometimes antibiotics are used in the vaccine manufacturing process to prevent bacterial contamination during production.  The actual amount of antibiotics that are found in some vaccines is extremely small. For instance, in the MMR vaccine, there is 0.025 mg of Neomycin per dose. To put that in perspective, about 800 MMR vaccines would contain an amount of neomycin equal to the weight of one snowflake.


Most vaccines are “single dose” vaccines meaning that a vaccine vial is only used once for one dose, for one person. But there are a few “multi-dose” vaccines where the vial is used several times. For multi-dose vaccines, preservatives are needed to prevent contamination from bacteria or fungus.

A commonly used preservative in flu vaccines is a mercury called Thimerosal. There has been concern about thimerosal because some people have confused it with a type of mercury that, at high levels, can be toxic to people. But not all types of mercury are harmful. Thimerosal is an ethylmercury which is safe because it breaks down and is excreted from the body rapidly. It is different from methylmercury which is the type of mercury that can accumulate in a person’s body and cause harm at high levels. Methylmercury is the type of mercury found in fish and other animals in our food chain.

Many chemical compounds have complex and unfamiliar names which can confuse or concern people. However, Thimerosal is actually an organic compound and has been used in vaccines, other drugs, and even contact solutions since the 1930s. Today, there are only a few vaccines that use thimerosal because vaccine manufacturers have found cost-effective ways to make single-use vials. Thimerosal has been rigorously studied in the United States and many other countries but for people who still have concerns about it, there are thimerosal-free vaccines available.

Learn more about Thimerosal:


There is a long road from when a vaccine is manufactured to when a patient gets it, and that is where stabilizers come in. Stabilizers protect a vaccine during storage and transport and ensure it will work once it gets to the patient. Common stabilizers include sugars or gelatin. Think of stabilizers like the ice used to keep meat from going bad while it’s being transported from the farm to the grocery store.

How do I know this information is credible?

We work for parents so we make sure that parent concerns are addressed using facts and science and our content is reviewed by experts who have spent their careers studying vaccines. Learn more about how we ensure we are bringing you the best information to help you make healthy choices for your family.

Chemical Compound Confusion


The Language of Science is precise but not always accessible or understandable. Just because something has a long, complex scientific name doesn’t mean it’s unnatural or dangerous.

  • Saccharomyces cerevisiae is baker’s yeast
  • Musa acuminata is just a banana.

So don’t assume a long, strange-sounding name is a bad thing.

Another common misperception is that certain ingredients, like aluminum, are dangerous. Too much of anything, even water, can be dangerous but many ingredients people assume are harmful are naturally found in the body, like aluminum.

Most of us do not know all the nuances of an ingredient, like what and how much of something is helpful or harmful. Instead, we can learn to identify credible sources and trust them to help inform our health decisions.

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