Hippopotamuses are often observed with a reddish fluid coating their skin, leading to the popular misconception that they “sweat pink.” However, hippos do not produce sweat in the same manner as humans or other mammals. Instead, this unique reddish secretion is a remarkable biological adaptation, providing various protective benefits for these large semi-aquatic animals.
Unpacking the “Pink Sweat” Myth
The reddish substance on a hippo’s skin is not sweat, nor is it blood, despite its historical nickname “blood sweat.” This viscous, oily fluid is a glandular secretion, produced and released from specialized subdermal glands. While initially colorless, it quickly undergoes a chemical reaction upon exposure to air, developing its characteristic reddish-orange hue. This transformation occurs within minutes, and the secretion can then gradually turn brown as its components polymerize.
Hippos do not possess conventional sweat glands for thermoregulation. This unique fluid serves multiple purposes beyond temperature control. It forms a protective layer over the hippo’s skin, which is surprisingly sensitive despite their massive size. This oily secretion helps to maintain skin health and integrity, crucial for an animal that spends significant time both submerged in water and exposed to the sun.
The Protective Power of Hippo Secretion
The hippo’s unique secretion plays a multifaceted role in protecting its skin from environmental challenges. One primary function is acting as a natural sunscreen, shielding the animal’s sensitive, almost hairless skin from intense ultraviolet (UV) radiation. The pigments within the fluid absorb UV light, effectively preventing sunburn and skin damage. This built-in UV protection is important, as hippos spend up to 16 hours daily submerged in water, often with their backs exposed to the sun.
Beyond sun protection, the secretion also possesses potent antiseptic and antibiotic properties. This is important for hippos, which frequently sustain wounds. The acidic nature of the secretion inhibits the growth of pathogenic bacteria, helping to prevent infections in open wounds, even in the aquatic environments they inhabit. This oily layer also acts as a natural moisturizer, preventing the hippo’s skin from drying out and cracking when out of the water. It also helps prevent the skin from becoming waterlogged while submerged.
The Science Behind the Reddish Hue
The reddish-orange color of the hippo’s skin secretion is attributed to two specific chemical compounds: hipposudoric acid (red) and norhipposudoric acid (orange). These pigments are unique to hippos and are synthesized by the animal, rather than being derived from their diet. They are non-benzenoid aromatic compounds that are notably acidic.
When secreted, the fluid is colorless, but upon contact with oxygen in the air, these compounds oxidize and develop their vibrant colors. Hipposudoric acid is particularly effective at inhibiting bacterial growth, contributing to the secretion’s antiseptic qualities. Both hipposudoric and norhipposudoric acids also absorb UV light, providing the hippo with natural sun protection. These compounds remain stable for several hours on the hippo’s skin before eventually polymerizing and turning a darker brown.