Adulterant

An adulterant is a pejorative term for a substance found within other substances such as food, fuels or chemicals, although it should not be present for some reason. It will not normally be present in any specification or declared contents of the substance, and may not be legally allowed. The addition of adulterants is called adulteration. The most common reason for adulteration is the use by manufacturers of undeclared materials that are cheaper than the correct and declared ones. The adulterants may be harmful, or reduce the potency of the product, or they may be harmless.

The term "contamination" is usually used for the inclusion of unwanted substances due to accident or negligence rather than intent, and also for the introduction of unwanted substances after the product has been made. Adulteration therefore implies that the adulterant was introduced deliberately in the initital manufacturing process, or sometimes that it was present in the raw materials and should have been removed, but was not.