Do some frogs have poison in their skin?

Yes. Frogs (and toads) have mucous glands all over their skin to help keep their skin lubricated. If frogs do not keep their skin moist they will dry out and die. In some species, such as the poison dart frogs, the secretions from these glands are highly toxic. All frogs and toads have a degree of these poisons, even if it is only in retrace amounts, but in some species the concentration of toxins is much greater, providing an effective defence mechanism.

The mucous glands in frogs' and toads' skin is different from the parotid glands which some species of toads have just behind their eyes, which contain irritants and other toxins to deter predators.