Vaccines work because they contain certain molecules from the disease causing organism (the pathogen) which are then injected into the body to trigger an immune response. These molecules are known as the antigen and are the major active ingredient in a vaccine.

In addition to the antigen, vaccines commonly also contain a number of other ingredients, such as preservatives, adjuvants, antibiotics and other chemicals. Parents are understandably concerned about the use of these chemicals and the potential danger they pose to their children.

Let’s look at three of the most potentially dangerous vaccine ingredients, as well as some of the vaccines they are found in and the potential problems these additives can cause:

• Formaldehyde is used both to inactivate viruses so they can’t cause disease and to detoxify bacterial toxins, such as the diphtheria toxin. Even though most physicians and researchers say that the amount of formaldehyde is too small to cause any problems, the chemical is classified as a carcinogen (causes cancer) by the U. S. Environmental Protection Agency. The diphtheria, pertussis and tetanus vaccine (known as the DTap) contains formaldehyde, as does the inactivated hepatitis A vaccine, some brands of the hepatitis B vaccine, the influenza vaccine and meningococcal vaccine.

• Thimerosal is a preservative that contains mercury and this chemical can be harmful, especially for children. Thimerosal is a neurotoxin as well as a carcinogen and can disrupt the immune system of a developing infant. Exposure to thimerosal by the fetus and the developing child can cause developmental delays and motor impairment. After realizing the dangers of thimerosal, this ingredient was removed from U.S. vaccines in 1999, however thimerosal remains an ingredient in most flu vaccines as well as in most tetanus shots.

There is also great concern by some parents that mercury found in thimerosal could be a cause of autism. A 2015 scientific review article bluntly states that thimerosal is a poison even at very low levels with a profusion of studies showing harmful effects, even at the levels found in today’s vaccines.

• Aluminum is used as an adjuvant in many vaccines. An adjuvant is an additive that increases the immune response to the antigen. Aluminum is a neurotoxin and there is evidence it could also cause long term brain inflammation as well as immunological disorders in humans. Aluminum is found in the tetanus vaccine (DT) as well as the diphtheria, pertussis and tetanus (DTap) vaccine, the diphtheria, tetanus, pertussis, polio and haemophilus influenzae type B (DTap-IPV/Hib) vaccine, both hepatitis A and B vaccines and the human papillomavirus (HPV) vaccine.

Besides these three common vaccine additives, there are many other chemicals which are routinely added to vaccine preparations. To see exactly what chemicals are in any of the vaccines you are considering for your child, ask your pharmacist or your healthcare provider for a copy of the vaccine package insert for that particular vaccine.