Pigs roll in mud to protect their skin from sunburn, using it as a natural sunscreen.

Pigs are biologically vulnerable to solar radiation because they lack a thick coat of fur and have very few functional sweat glands. Unlike humans, who sweat to cool down, pigs depend on external moisture for thermoregulation. Research from the University of Veterinary Medicine in Vienna demonstrates that wallowing is a vital behavior for both temperature control and skin health.When mud dries on a pig's skin, it acts as a physical shield that blocks harmful ultraviolet (UV) rays. This is especially critical for light-skinned breeds, which are particularly prone to severe sunburn and even skin cancer. The dried mud functions as a natural SPF, similar to how elephants and rhinoceroses use dirt to protect their hides.Beyond sun protection, the evaporation of water from the mud provides a cooling effect that lasts longer than clear water alone. A 2011 study published in Applied Animal Behaviour Science suggests that wallowing may have evolved from an ancestral trait in hippopotamuses, pigs' closest living relatives. This behavior also serves as a defense mechanism against parasites like lice and ticks.By coating themselves in mud, pigs create a barrier that prevents biting insects from reaching their skin. This multi-purpose behavior is so critical that animal welfare standards often require farms to provide wallowing areas. Without access to mud or water, pigs can suffer from heat stress and painful skin lesions within hours of direct sun exposure.