Pigs lack functional sweat glands and cannot perspire, so they must roll in mud to cool down.

Pigs are endothermic mammals, but they lack an effective thermoregulation system based on perspiration. Although they possess sweat glands, these remain largely inactive and ineffective for cooling purposes. This biological limitation makes pigs highly vulnerable to heat stress when temperatures exceed 85°F (29°C).To survive in warm conditions, pigs engage in wallowing behavior. Research from the University of Veterinary Medicine in Vienna demonstrates that wallowing is a critical survival mechanism, not merely a behavioral quirk. The mud coating on their skin evaporates much more slowly than water alone, creating a prolonged cooling effect that can reduce their skin temperature by up to 3.6°F (2°C).Additionally, pigs have sparse hair coverage and light skin, making them extremely susceptible to ultraviolet radiation damage. Mud acts as a natural sunscreen, blocking harmful UV rays and preventing painful sunburns. It also functions as a protective barrier against external parasites such as lice and ticks, which can cause infections and anemia in livestock.In modern agriculture, farmers must provide misters or cooling pads to prevent heat stroke in pigs. Studies published in the Journal of Animal Science show that without these cooling interventions, a pig's internal temperature can rise to dangerous levels rapidly. This unique physiological constraint explains why the common expression "sweating like a pig" is scientifically inaccurate.