You may have heard that vaccines contain all types of crazy ingredients that sound as though they don’t belong in a medical product. The truth is that a very small group of very vocal, but misinformed, individuals have made false accusations regarding the safety of vaccines and their ingredients. In most instances these allegations are just wrong. In other cases, the claims are from information taken out of context or are trying to purposely mislead people.

The main ingredients in vaccines are antigens, which are small amounts of the bacteria or virus against which the person is being vaccinated. Antigens are the parts of the vaccine that encourage your immune system to create antibodies to fight against future infections. To make sure that the vaccines cannot cause the disease you are trying to protect against, the antigens are altered or weakened. Learn more about how vaccines are made and how they work.

Like many of the foods we eat and beverages we drink, vaccines also contain a small amount of additional ingredients, and each has a specific, necessary function. These ingredients may be added to the vaccine to make it more effective, sterile and/or safe. These additional ingredients have been studied and are safe for humans in the amount used in vaccines.

In fact, the amount of these additional ingredients in vaccines is much less than children encounter in their environment, food and water. As the saying goes, “the dose makes the poison.” In other words, any chemical – even water or oxygen – can be toxic or even deadly in large enough quantities.

Sometimes a child may be sensitive to one of the components of a vaccine, and an allergic reaction may result. For this reason, you should discuss any allergies your child may have with your healthcare provider. Below are the ingredients that may be found in certain vaccines and their purpose.

Preservatives

When an individual vaccine dose is drawn from a multi-dose vaccine vial with a new needle, it is possible for bacteria or fungus to get into the vial, which could be very dangerous to the people getting the shots. To prevent this contamination, a preservative is added to the vaccine vial.

Since 1968, the United States Code of Federal Regulations has required the addition of a preservative to multi-dose vials of vaccines; and worldwide, preservatives are routinely added to multi-dose vials of vaccine. Tragic consequences have followed the use of multi-dose vials that did not contain a preservative (including deaths) and are the driving force for this requirement.

Having safe, multi-dose vials of vaccines available for us to use is very important, especially when a large number of people need to be vaccinated quickly, which could be the case during a flu, coronavirus or other disease pandemic.

Thimerosal

Thimerosal is a preservative used in multi-dose vials of flu vaccines to prevent contamination with bacteria or fungus, which could be deadly.

Thimerosal is made from a type of mercury call ethylmercury. This kind of mercury is broken down by the body and clears out of the blood quickly.

Ethylmercury is very different than methylmercury.

Methylmercury is found naturally in the environment. It is also the kind of mercury that is found in fish like salmon and shellfish; and also in many everyday products, foods and drinks.

Methylmercury accumulates in the body and takes much longer to remove from the body. A buildup of methylmercury in the body is usually due to eating certain types of fish or other drinks or food, and high amounts can harm the nervous system. Over a lifetime, everyone is exposed to some methylmercury.

Even though there was no evidence that thimerosal in vaccines was dangerous, in 2001, it was removed from vaccines in the U.S. in an effort to reduce overall mercury exposure among infants. To keep vaccines safe from contamination without the use of thimerosal or other preservatives, they were either reformulated or put into single-dose vials. Now, the only vaccines in the U.S. that use thimerosal as a preservative are flu vaccines in multi-dose vials. (Thimerosal-free, single-dose vials of flu vaccine are also available in the U.S.) There is no evidence that the small amounts of thimerosal in flu vaccines cause any harm, except for minor reactions like redness and swelling at the injection site.

To learn more about the thimerosal content in FDA-approved seasonal flu vaccines, visit the Thimerosal and Vaccines page on the the Food and Drug Administration (FDA) website.

MMR (measles, mumps, and rubella), chickenpox (varicella), inactivated polio (IPV), and pneumococcal conjugate vaccines (PCV) never contained thimerosal as a preservative.

No credible scientific studies have found an association between thimerosal in vaccines and autism. The studies used different methods to find out if there was any connection between thimerosal and autism. Some examined rates of autism a state or a country, comparing autism rates before and after thimerosal was removed as a preservative from vaccines. It is important to note that in the U.S. and other countries, the number of children diagnosed with autism has not gone down since thimerosal was removed from childhood vaccines. To read the studies yourself, visit our Vaccine Research section.

The Global Advisory Committee on Vaccine Safety, which provides independent, authoritative, scientific advice to the World Health Organization (WHO) on vaccine safety issues of global or regional concern, has also concluded that there is no evidence of toxicity in infants, children or adults exposed to thimerosal in vaccines.

You can learn more about vaccines and autism on the Autism Science Foundation website.

Watch Now: Is there mercury (thimerosal) in vaccines? Is that dangerous?

Formaldehyde

Formaldehyde is a colorless gas that is a byproduct of metabolism so it is already present in the human body. People also encounter formaldehyde every day in the environment. It is used in making building materials and many household products, and formaldehyde also gets into the air through car tailpipe emissions.

Formaldehyde is used is used to inactivate bacterial products for toxoid vaccines (DTaP and Tdap), and to kill unwanted viruses and bacteria that might contaminate the vaccine during the manufacturing process. Most formaldehyde is removed from the vaccine before it is packaged. In very small amounts, formaldehyde is not dangerous. In fact, there is more formaldehyde in a pear than in any one vaccine.

Learn more about formaldehyde in vaccines from Vaccine Education Center at Children’s Hospital of Philadelphia.

Aluminum

Aluminum is everywhere. It is commonly found in food, health-and food-related products, water, infant formula and even breast milk. And for over 75 years, very small amounts of aluminum (aluminum gels or aluminum salts) have been added to some vaccines as “adjuvants” to help boost the body’s immune response. Without the use of these aluminum gels/salts in these vaccines, healthcare providers would need to give more doses of the vaccine or there there would be less immunity provided by the vaccine, and therefore less protection from the disease.

Watch Now: Can you explain why adjuvants, like aluminum, are in some vaccines?

Learn more about aluminum in vaccines from the Vaccine Education Center at the Children’s Hospital of Philadelphia.

Adjuvants

Adjuvants, such as aluminum, are added to certain vaccines to help trigger a better immune response from your body. Without the adjuvant, we would need to give more doses of a vaccine or the vaccine would give us less immunity protection from the disease.

Watch Now: Can you explain why adjuvants, like aluminum, are in some vaccines?

Studies have shown there is no connection between adjuvants and the development of autoimmune diseases.

Residual Antibiotics

Antibiotics are added to some vaccines to prevent the growth of bacteria during the vaccine manufacturing process and storage of the vaccine. No vaccine produced in the United States contains penicillin.

Learn more about how vaccines are made.

Egg Protein

Some vaccines, like MMR and some some flu vaccines, are prepared in eggs which means that some egg proteins are present in the final vaccine product. The egg proteins help manufacturers to grow enough of the virus or bacteria needed to make the vaccine. Based on scientific evidence, the American Academy of Pediatrics (AAP) states that the MMR vaccine can be safely given to all patients with egg allergies, including patients with a history of severe, generalize anaphylactic reactions to eggs. AAP also states that “children with egg allergy can receive influenza vaccine with no additional precautions than those considered for any vaccine.”

Additionally, the American Academy of Allergy, Asthma & Immunology (AAAAI) states “Studies show that flu vaccines can be safely administered to egg allergic individuals.” If you or your child are allergic to eggs, make sure to tell your doctor or healthcare provider before getting vaccinated.

Gelatin

Some vaccines contain gelatin to protect them against freeze-drying or heat during the transportation and storage process. People with severe allergies to gelatin should talk to their doctor or healthcare provider before getting vaccinated.

Religious leaders of the Muslim and Jewish communities have approved the use of vaccines containing gelatin.

Antifreeze

You may have heard that vaccines contain products such as antifreeze. This is not true. Antifreeze typically contains ethylene glycol, an unsafe and highly toxic (poisonous) component, or propylene glycol, a safer and less toxic option to ethylene glycol. Neither of these members of the glycol family of compounds is used in vaccines. In vaccines, polyethylene glycol is used to inactivate the virus in some influenza vaccines and is also used to purify other vaccines. Polyethylene glycol is approved by the FDA and considered non-toxic for medical and other uses.* It is used in a variety of products including skin cream, toothpaste, lubricating eye drops, laxatives, and as an anti-foaming agent in food. It is also used as an irrigating solution in surgical procedures.

* Victor O. Sheftel (2000). Indirect Food Additives and Polymers: Migration and Toxicology. CRC Press, 1114-1116.

Sources and Additional Resources

I’ve heard there are ingredients in vaccines that can harm children. Is this true? – Vaccinate Your Family Video FAQs

Vaccine Ingredients Q&A (Handout in English and Spanish) – Vaccine Education Center at Children’s Hospital of Philadelphia.

Vaccine Ingredients – Vaccine Education Center at Children’s Hospital of Philadelphia.

Common Ingredients in U.S. Licensed Vaccines – Food and Drug Administration (FDA)

Offit and Jew. Addressing Parents’ Concerns: Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals? Pediatrics. December 2003.

Vaccines Ingredients – Centers for Disease Control and Prevention (CDC)

Understanding Thimerosal, Mercury, and Vaccine Safety (Handout) – Centers for Disease Control and Prevention (CDC)

Vaccine Ingredients Sorted by Vaccines (Handout) – Centers for Disease Control and Prevention (CDC)/Pink Book