The skin of hippos is very sensitive and weak to dryness. If they do not stay moist with water or mud, their skin will crack easily. Hippos secrete a pink liquid called "blood sweat," which protects their skin from ultraviolet rays and bacteria. This liquid also has a healing effect. You can observe hippos sunbathing on land during sunny days or see them in the water with their faces and backs half out, not moving.