Today’s vaccines use only the ingredients they need to be safe and effective. A note on vaccine safety Vaccines go through comprehensive safety and effectiveness testing. The Food and Drug Administration (FDA) looks at the results of these tests to decide whether to license the vaccine for use in the United States. Learn more about vaccine safety. Each ingredient in a vaccine serves a specific purpose. For example, vaccine ingredients may: Help provide immunity (protection) against a specific disease Help keep the vaccine safe and long lasting Be used during the production of the vaccine Ingredients provide immunity Vaccines include ingredients to help your immune system respond and build immunity to a specific disease. For example: Antigens are very small amounts of weak or dead germs that can cause diseases. They help your immune system learn how to fight off infections faster and more effectively. The flu virus is an example of an antigen. Adjuvants , which are in some vaccines, are substances that help your immune system respond more strongly to a vaccine. This increases your immunity against the disease. Aluminum is an example of an adjuvant. Learn more about how vaccines provide immunity. Ingredients keep vaccines safe and long lasting Some ingredients help make sure a vaccine continues to work like it’s supposed to and that it stays free of outside germs and bacteria. For example: Preservatives , like thimerosal, protect the vaccine from outside bacteria or fungus. Today, preservatives are usually only used in vials (containers) of vaccines that have more than 1 dose. That’s because every time an individual dose is taken from the vial, it’s possible for harmful germs to get inside. Most vaccines are also available in single-dose vials and do not have preservatives in them. Stabilizers , like sugar or gelatin, help the active ingredients in vaccines continue to work while the vaccine is made, stored, and moved. Stabilizers keep the active ingredients in vaccines from changing because of something like a shift in temperature where the vaccine is being stored. Ingredients are used during the production of vaccines Some ingredients that are needed to produce the vaccine are no longer needed for the vaccine to work in a person. These ingredients are taken out after production so only tiny amounts are left in the final product. The very small amounts of these ingredients that remain in the final product aren’t harmful. Examples of ingredients used in some vaccines include: Cell culture (growth) material , like eggs, to help grow the vaccine antigens. Inactivating (germ-killing) ingredients , like formaldehyde, to weaken or kill viruses, bacteria, or toxins in the vaccine. Antibiotics , like neomycin, to help keep outside germs and bacteria from growing in the vaccine. Common questions about vaccine ingredients Learn more about the types of vaccine ingredients and why they’re used from the common questions below. Can vaccines with thimerosal cause mercury poisoning? A: No. Thimerosal has a different form of mercury (ethylmercury) than the kind that causes mercury poisoning (methylmercury). It’s safe to use ethylmercury in vaccines because it’s less likely to build up in the body — and because it’s used in very, very small amounts. Even so, most vaccines do not have any thimerosal in them. If you’re concerned about thimerosal or mercury in vaccines, talk with your doctor. Can people who are allergic to antibiotics get vaccinated? A: Yes. However, if you have an allergy to antibiotics, it’s a good idea to talk with your doctor about getting vaccinated. But in general, antibiotics that people are most likely to be allergic to — like penicillin — aren’t used in vaccines. Can people with egg allergies get vaccinated? A: Yes. People with egg allergies can get any licensed, recommended flu vaccine that’s appropriate for their age. They no longer have to be watched for 30 minutes after getting the vaccine. People who have severe egg allergies should be vaccinated in a medical setting and be supervised by a health care professional who can recognize and manage severe allergic conditions. Is the formaldehyde used in some vaccines dangerous? A: No. If formaldehyde is used to help produce a vaccine, only very small amounts are left in the final product. This amount is so small that it’s not dangerous — in fact, there’s actually more formaldehyde found naturally in our bodies than there is in vaccines made with formaldehyde. Is the aluminum used in some vaccines dangerous? A: No. Vaccines made with aluminum have only a very small amount of aluminum in them. For decades, vaccines that include aluminum have been tested for safety — these studies have shown that using aluminum in vaccines is safe. Get more information about types of vaccine ingredients.