In order to keep moist, toad skin contains glands that secrete a slimy mucous layer to protect the skin from drying out and help draw in oxygen through the skin. In the water, the mucous secretions help frogs retain a healthy balance of salt and water within their internal tissues. In many species, these glands are modified to produce toxins and other substances that will repel predators. Some toad skin toxins are being researched as potential pain medications.