Formaldehyde is a good example of the famous quote by Paracelsus, “the dose makes the poison.” 

We are all exposed to formaldehyde. We are exposed to formaldehyde in the air. Also, people, plants and animals all make small amounts of formaldehyde during cellular processes, so we are always making small amounts of formaldehyde in our bodies every day. Most of us never even realize we were exposed nor do we have any ill effects from these exposures. But formaldehyde can cause health issues for some people, particularly if they are exposed to large amounts over a long period of time (see “Health effects of formaldehyde” below). 

We talk about formaldehyde in relation to vaccines because in some cases it is used during the production process. As a result, it can be found in small quantities in certain vaccines. In this manner, is called a “manufacturing byproduct or residual.”

About formaldehyde

Formaldehyde is a colorless gas at room temperature. It can also be dissolved in water with methyl alcohol. In this form, it is called formalin. Formalin contains about 30%-50% formaldehyde and 10%-20% methyl alcohol. Formaldehyde is flammable and has a distinct odor. Formalin can release vapors that also have this distinct odor.

People are most often exposed to the gaseous form of formaldehyde. Formaldehyde vapors get into the air from a variety of sources because formaldehyde is used in many products and industries. People can also be exposed to formaldehyde through their skin and by eating foods that contain small amounts of formaldehyde. Formaldehyde can be present in foods naturally (e.g., plant-based foods, like fruits), added as a preservative, or produced during the cooking process.

Some examples of where formaldehyde can be found include:

• Power plants
• Manufacturing facilities
• Automobile exhaust
• Tobacco smoke
• Building materials, like insulation, plywood and particle board
• Glues, adhesives, paints and paper products
• Some cosmetics, like fingernail and hair care products
• Fabrics
• Embalming materials
• Medical laboratories
• Fertilizers and pesticides

People who work in industries in which formaldehyde is frequently present at high levels are more likely to experience negative health effects from exposure to this chemical.

Formaldehyde in vaccines

Formaldehyde is used in a diluted form during the vaccine manufacturing process. Despite purification of the vaccine, small quantities of formaldehyde may still be found in some vaccines (see table below). 

Formaldehyde content of vaccines licensed for use in the U.S.

The average amount of formaldehyde a young infant could be exposed to in the first two years of life could be as high as 0.7 – 0.8 milligrams (mg). This quantity of formaldehyde is considered safe for a few reasons:

• All people have detectable amounts of formaldehyde in their bodies because it is used in different ways, such as to make DNA and amino acids. Amino acids are the building blocks of proteins. People generally have about 2.5 micrograms (mcg) of formaldehyde per milliliter (ml) of blood.
  
  If a 2-month-old weighs about 5 kilograms (kg), which is about 11 pounds, and they have an average blood volume of about 85 ml per kg, they would have about 1.1 mg of formaldehyde in their blood. That amount is between 10 times and 220 times more than the amount they would be exposed to in any single vaccine.
• Amounts of formaldehyde at least 600 times greater than those contained in vaccines have been fed safely to animals in drinking water.

Health effects of formaldehyde

Formaldehyde is quickly broken down into other chemicals in the body. For this reason, any health effects tend to result from ongoing exposure to high levels of this chemical. The effects are not cumulative, meaning if the exposure decreases, so does the risk of experiencing any negative health effects.

The most common and established health effects occur when there are high levels of formaldehyde in the air. In these situations, people can experience irritation of their eyes, nose and lungs, but not everyone will experience these types of effects.

Ongoing exposure to high levels of formaldehyde can damage DNA, the building blocks of genes. This damage can cause certain cancers, including those of the nose and throat and some types of leukemia. Importantly, most studies that found a link between formaldehyde exposure and cancer have been in people who work in industries where they are exposed to large quantities of formaldehyde over long periods of time, such as people who embalm bodies, those who work in certain manufacturing industries, and healthcare workers.

Formaldehyde in vaccines and health

While formaldehyde can cause certain types of cancer, formaldehyde from vaccines does not cause negative health effects. Three points are important:

1. The amounts contained in vaccines are too low to cause cancer.  
2. Exposure to formaldehyde from vaccines is infrequent, whereas ongoing exposure is a necessary component of negative health effects in the form of cancer. 
3. The type of cancer most commonly associated with formaldehyde is that of the nose and throat — a direct result of breathing in formaldehyde over a long period of time. Formaldehyde in vaccines does not contribute to exposures in the airways.
4. We are exposed to far more formaldehyde in our bloodstream from normal physiological processes than we would ever be exposed to from vaccines.

Summary

We all have formaldehyde in our bodies, and our cells produce formaldehyde. We are also exposed to formaldehyde in the air because it is used in many products and produced during manufacturing or other processes. 

Most people never have negative health effects from exposure to formaldehyde, but this chemical can cause such effects if exposures are too high. Exposure to high levels in the air can cause short-term effects, like irritation of the eyes, nose and lungs. Exposure to high levels over long periods of time can cause cancers of the nose and throat or certain types of leukemia. 

Although some vaccines contain small quantities of formaldehyde that remain from the manufacturing process, exposure to formaldehyde from vaccines is minor and rare compared with other exposures. As such, families can be reassured that formaldehyde exposure from vaccines is safe.

References

Mitkus RJ, Hess MA, Schwartz SL. Pharmacokinetic modeling as an approach to assessing the safety of residual formaldehyde in infant vaccines. Vaccine 2013;31:2738-2743. 
The authors estimated the levels of formaldehyde in blood and total body water following exposure to formaldehyde-containing vaccines and compared them with endogenous background levels. (Formaldehyde is a natural product of single-carbon metabolism.) Following a single intramuscular dose of 200 micrograms of formaldehyde, which is equivalent to the amount of formaldehyde received from DTaP, Hib, IPV, and hepatitis B at a single office visit, formaldehyde was completely removed from the site of injection within 30 minutes. Peak concentrations of formaldehyde in blood were estimated to be less than 1 percent of the level of formaldehyde naturally produced by the body. The authors concluded that formaldehyde in vaccines is safe.

American Cancer Society. Formaldehyde and Cancer Risk. Accessed July 6, 2026.

California Department of Public Health. Formaldehyde. Accessed July 6, 2026.