A toxin or poison is a substance that causes a bad reaction in the body. Toxins can be breathed in, absorbed through the skin or mucous membranes, consumed through the mouth, or injected into the body via a needle or insect or snake bite.. Examples of toxins or poisons include spider and snake venom, chemicals found in detergents or other household products, poisonous gases, medications, chemicals in poisonous plants and chemicals in tobacco smoke. Some scientists use the term "toxin" when referring only to poisons created biologically from animals, fungi, plants, bacteria and the like; however, the term is often used to describe any poison. Some toxins, like botulinum, have been used for medical purposes, and many others may prove helpful in small doses for various conditions.