Body cleansing or detoxification is a treatment in alternative medicine which proponents claim rid the body of accumulated harmful substances that exert a negative effect on individual health. Critics argue that such cleansings are often unnecessary, and are based on questionable or disproved scientific claims.

In the 19th century, cleansing proponents described the large intestine as a sewage system, claiming that stagnation caused toxins to be absorbed by the body. Laxatives, purges, and enemas were routinely recommended to prevent the accumulation of waste which could lead to this "autointoxication".

Various modalities of body cleansing are used, employing physical treatments (e.g. colon hydrotherapy), dietary restrictions (e.g. avoiding foods) or dietary supplements. Some variants involve the use of herbs and supplements that purportedly speed or increase the effectiveness of the process of cleansing. Naturopathic and homeopathic remedies are also promoted for cleansing. Cleansing agents and processes may be promoted as targeting specific organs, such as fiber for the colon or juices for the kidneys. Others are represented as useful for 'whole body' cleansing, sometimes with the goal of eliminating unidentified 'parasites'.

Quackwatch describes body cleansing and detoxification as an elaborate hoax used by con artists to cure nonexistent illnesses. The 'toxins' that are removed have been described as invented to give promoters something pretend they can fix. Medical experts state that the body cleansing is unnecessary since the body is actually very good at maintaining itself, with several organs dedicated to cleansing the blood and gut.