Hippos do not sweat, but often submerge themselves in water to keep cool during the day. They produce a substance that looks like sweat, but is actually a natural sunscreen that turns red in the sun. The fluid was previously believed to be a mix of blood and sweat.
Because hippos require water deep enough to submerge their entire bodies, they are highly adapted to a semi-aquatic lifestyle. Their eyes and nostrils are placed on top of their heads so they can breathe and see with minimal exposure to the air. Additionally, their nostrils can close to allow for full submersion.