Touching frogs or toads does not cause warts. The notion that frogs induce warts in humans is a myth, and warts are caused by certain viruses in the human papillomavirus family.
The frog-wart myth likely started because of the small bumps visible through a frog's skin, but the bumps have nothing to do with warts. They are mucus or poison glands that release toxins when the amphibians feel threatened. Most toxins are harmless, sometimes causing a minor skin rash or stomachache if ingested. Certain frogs and toads, however, secrete poisons that can lead to cardiac or neurological failure or even death. These threatening amphibians are typically found in humid, tropical regions.