Disinfection By-products (DBPs) Factsheet

Disinfection by-products (DBPs) are formed when disinfectants like chlorine interact with natural organic materials in water, such as in chlorinated drinking water and chlorine-treated swimming pools. DBPs can be found in the air during activities such as showering, bathing, dishwashing, and swimming. The most common type of DBPs are trihalomethanes (THMs).

How People Are Exposed to DBPs

People are exposed to DBPs by drinking chlorinated or brominated water and by breathing in air containing DBPs. The skin also absorbs DBPs during bathing and swimming. After exposure, DBPs remain in the body for only a short period of time.

How DBPs Affect People’s Health

Chronic exposure to DBPs may increase risk of cancer. Humans exposed to unusually large amounts of some DBPs could experience liver damage and decreased nervous system activity.

Levels of DBPs in the U.S. Population

In the Fourth National Report on Human Exposure to Environmental Chemicals (Fourth Report), CDC scientists measured four different THMs in the blood of at least 1,222 participants aged 20–59 years who took part in the National Health and Nutrition Examination Survey (NHANES) during 2003–2004. By measuring THMs in blood, scientists can estimate the amounts of the THMs that have entered peoples’ bodies.

CDC scientists did not find detectable blood levels of THMs in all participants. Levels were similar to those seen in small past studies.

Finding a measurable amount of one or more THMs in blood does not imply that the levels of DBP cause an adverse health effect. Biomonitoring studies of blood THMs can provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of THMs than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.

Additional Resources

Agency for Toxic Substances and Disease Registry

Environmental Protection Agency

Page last reviewed: July 18, 2022