What is it
Keratin is a type of fibrous tough and insoluble protein. It's what your hair is mostly made of, and it's in your skin. Other animals have it in their feathers, fur, skin and scales.
Keratin forms a tough, impervious, waterproof layer that protects animals, stopping unwanted substances in the outside world from getting into their bodies. It also builds up as thick layers of skin in areas of the body that get exposed to lots of wear and tear (callouses).
Keratin in frogs
A frog needs its skin to be thin, moist and impervious to most things from the outside. But it also breathes through its skin. Even though it has simple lungs, these don't give them all the oxygen they need. They have to absorb oxygen from the air or via the water through their skin. If their skin was full of keratin, they wouldn't be able to do this.
Frogs only have keratin in the parts of their body that get exposed to wear and tear - such as their hands and feet, and the places where their legs rub against their bodies and at the knee and elbow joints. Tadpoles only have keratin around their mouths, to help them make the mouth tough so they can scrape food from their environment. But as they develop into frogs, they grow keratin in other parts of their bodies.
Chytrid fungus and Keratin
The deadly Chytrid fungus causes a disease called chytridiomycosis. It only attacks the parts of a frog's skin that has keratin in it. Tadpoles can be infected around their mouths, but this isn't enough to kill them. It's only when they start turning into frogs, and grow keratin in other areas, that the Chytrid fungus can spread throughout their bodies and in the case of Dwarf African Frogs kills them within 3 months of becoming a frog. Just about the time they've been sold to an unsuspecting new owner.
Certain species of frogs, like the aquatic African Clawed Frog is, for some reason scientists do not yet understand, immune to the fungi. They simply carry the fungus, infectiing the water they travel through or other amphibians they touch.
As the amphibian gets parts of its skin eaten away it loses electrolytes and salts from within its body. This causes the skin to peel and exposes the inner parts of the body to water and it gets infections and usually dies.
- See article Chytrid fungus on how to kill the fungi.