Hailed as one of the Ten Great Public Health Achievements in the 20th century by the U.S. Centers for Disease Control and Prevention (CDC), vaccines save an estimated 2.5 million lives every year from infectious diseases.

As a result of vaccinations, diseases like diphtheria, once deadlier than cancer, have been drastically reduced, even eliminated. The benefits of vaccines are clear: Routine immunizations given to the 78.6 million children born in the U.S. over the past two decades will prevent 322 million illnesses, 21 million hospitalizations and 732,000 deaths over the course of their lifetimes, according to the CDC.

Vaccines work thanks to innovations in biotechnology and chemistry. By introducing a modified or “imitation” version of a disease like polio or measles to a person’s immune system, the body is able to recognize and fight off future exposure to the disease. As a result, vaccines work with the body’s natural defenses to help it develop immunity to disease.

To ensure vaccine safety, the U.S. Food and Drug Administration (FDA) regulates the development, testing and licensing of the ingredients used in vaccines through a rigorous multiphase approval process that can take 10 or more years. Even after approving a vaccine, FDA continuously monitors its safety.

Although vaccines are now commonplace and have proven effective at eliminating once deadly diseases, incorrect information can spread quickly through social media, leading to concerns about vaccines and their ingredients. Chemical ingredients are added to vaccines for a variety of purposes – some are added to inactivate a virus or bacteria and stabilize the vaccine, while others are added to preserve the vaccine and prevent it from losing its potency over time.

Here’s some additional information about common vaccine ingredients that you may have questions:

  • Aluminum gels/salts: Aluminum is one of the most common chemical elements in nature and is found in air, food and water. Tiny amounts of aluminum are added to some vaccines to help the body build stronger immunity against the virus in the vaccine.

Aluminum additives are used in vaccines for viruses such as hepatitis A, hepatitis B, and diphtheria-tetanus-containing vaccines, among others. Health officials recommend these vaccines for babies and young children, which sometimes leads parents to question the safety of aluminum in the shots. However, babies already have a small naturally occurring amount of aluminum in their bloodstreams, about 5 nanograms (a nanogram is equal to one billionth of a gram) from infant formula or breast milk. The amount of aluminum in a vaccine is far below the amounts that babies are naturally exposed to. According to FDA, vaccines containing aluminum have a demonstrated safety profile based on more than six decades of use and are only rarely associated with negative reactions, such as skin irritation or swelling.

  • Antibiotics: Certain antibiotics, including neomycin, polymyxin B, streptomycin, and gentamicin, can be used in the production of some vaccines to help prevent bacterial contamination and fungus growth. For example, during the production of an influenza virus vaccine, antibiotics are used to reduce bacterial growth in the egg ingredients, which are not naturally sterile and could otherwise contaminate the vaccine.
  • Chicken protein: Vaccines may contain very small amounts of the culture material used to grow the virus or bacteria used in the vaccine, such as chicken egg protein. For example, the most common way that flu vaccines are made is through an egg-based manufacturing process that has been in existence for more than 70 years.
  • Formaldehyde and other preservatives: Tiny amounts of formaldehyde have long been used in the manufacture of viral and bacterial vaccines. In fact, formaldehyde is found everywhere, our bodies produce it, and we exhale it at concentrations of up to a few parts per billion. The amount of formaldehyde present in some vaccines is so small compared to the concentration that occurs naturally in the body that it does not pose a safety concern.In vaccines, formaldehyde is used to inactivate a virus before it can cause the disease the person is being vaccinated against (for example, the polio virus used to make polio vaccine) and to detoxify bacterial toxins, such as the toxin used to make the diphtheria vaccine. Preservatives like formaldehyde also are added to some vaccines to prevent the growth of bacteria or fungi that could be introduced into the vaccine during actual vaccination.
  • Sugars and other stabilizers: Sugar is sometimes used as a stabilizer to help the vaccine maintain its effectiveness during storage and transit. Vaccines are shipped all around the globe; it’s critically important that they work when needed, and don’t degrade or lose effectiveness during the heat and cold of shipping. Other stabilizers added to vaccines include lactose and amino acids such as glycine or the monosodium salt of glutamic acid, and proteins such as human serum albumin or gelatin.

Interested in learning more about chemicals and safety? Read about common chemical myths and facts here.