Bentonite clay is an absorbent, impure clay made of aluminium phyllosilicate and other dominant elements, including potassium, sodium and calcium, according to Wikipedia. It is formed from volcanic ash and has several medical applications.
Wellness Mama explains that bentonite clay is commonly used in detoxification products and helps to balance bacteria in the gut. It is used in bulk laxatives and other over-the-counter digestive aids.
Bentonite clay is also an ingredient in many dermatological products. As Wikipedia points out, it is used to protect against exposure to urushiol, the active irritant in poison ivy. It calms itching and pain from burns, cuts, eczema, chicken pox, insect bites and psoriasis.