Captivity isn't natural, however. You get warts from touching frogs and toads. You get warts from catching certain human viruses, not from amphibians. The slimy skin of the frog keeps it moist when it is out of the water. The bumpy skin of toads and some frogs helps camouflage them in their habitat.
All toads are poisonous and can kill people.
All toads have lumps on the back of their heads, parotoid glands, that produce a chemical substance. In some toads, this makes them taste terrible to the animal that is trying to eat them. A few species on every continent, however, do prodice highly toxic substances that can be harmful to humans. They secrete the substance in self-defense, such as when they feel like they are about to be somebody's dinner. The poison from the poison arrow frogs in South America is is obtained only after they hold the frogs over a fire.