Newt
Newts, as with salamanders in general and other amphibians, serve as bioindicators because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the pH level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.
Newt
Many newts produce toxins in their skin secretions as a defence mechanism against predators. "Taricha" newts of western North America are particularly toxic. The rough-skinned newt "Taricha granulosa" of the Pacific Northwest produces more than enough tetrodotoxin to kill an adult human, and some Native Americans of the Pacific Northwest used the toxin to poison their enemies. However, the toxins are only dangerous if ingested, and the newts can easily and safely live in the same ponds or streams as frogs and other amphibians, or be safely kept as pets. The only predators of "Taricha" newts are garter snakes, some having developed a resistance to the toxin. Most newts can be safely handled, provided the toxins they produce are not ingested or allowed to come in contact with mucous membranes or breaks in the skin. After handling, proper hand-washing techniques should be followed due to the risk from the toxins they produce and bacteria they carry, such as "Salmonella". It is, however, illegal to handle or disturb great crested newts in the UK without a licence.