Hippos do not have real sweat glands but do have a pink secretion. However, a viscous alkaline secretion (pH 8.5–10.5), colorless to reddish-brown,is produced by large, subdermal glands (distributed at a density of about 1/cm2 ). This secretion imparts a pinkish tinge to the body and has antiseptic properties, preventing infections and sunburn and helping in thermoregulation (like sweat).
The skin serves to control body temperature primarily through regulation of evaporation, which is very high compared with other mammals, and is particularly high when the skin is wet with the secretion from the subdermal glands. This led Eltringham (1999) to suggest that temperature control is not achieved through any mechanism akin to sweating unless the secretion functions like sweat and may not be able to control the rate of water loss from the body.
Whether or not the secretion serves the same function as sweat, Common Hippos maintain a constant core body temperature of around 36°C even while on land (though body temperature is certainly also controlled by using its aquatic environment as a means of cooling down). When dry, it gives a glossy, paint-like appearance.