The hippopotamus, one of Africa’s largest land mammals, possesses a unique physiological feature: a thick, reddish fluid that appears to ooze from its skin. This substance, often mistakenly referred to as “blood sweat,” is a complex secretion vital to the animal’s survival in its semi-aquatic environment. While the red liquid suggests injury, this biological compound provides the hippo with protection against the intense African sun and the threat of infection.
Secretion: Dispelling the ‘Sweat’ Myth
The fluid is not produced by traditional sudoriferous (sweat) glands, despite the popular misconception. Instead, the substance is secreted from specialized, enlarged subcutaneous glands located just beneath the skin’s surface. These glands continually produce and release the viscous fluid, which forms a protective layer over the hippo’s relatively thin and sensitive epidermis.
When first secreted, the fluid is colorless and transparent, resembling a mucus or oily discharge. Upon contact with the air and sunlight, however, it quickly undergoes a chemical reaction that causes its dramatic change in color. Within minutes, the transparent fluid oxidizes, turning a vibrant red or reddish-orange hue. Over several hours, the exposed secretion continues to polymerize, eventually hardening into a brownish, sticky crust that remains on the animal’s skin.
The Chemical Components and Color
The brilliant red and orange coloration of the hippo’s secretion is due to the presence of two highly acidic pigment compounds. The primary red pigment is named hipposudoric acid, and its orange counterpart is called norhipposudoric acid. Both are chemically classified as conjugated organic compounds that absorb light in the visible spectrum.
These pigments are not obtained from the hippo’s diet but are synthesized internally by the animal through metabolic pathways. The compounds are thought to be derived from the amino acid tyrosine, which is a common building block for many biological molecules. The final color displayed on the hippo’s skin is determined by the specific ratio of the red hipposudoric acid to the orange norhipposudoric acid in the mixture. The chemical structure of these pigments is based on a three-ring fluorenoid nucleus.
Essential Dual Protective Functions
The complex chemistry of hipposudoric and norhipposudoric acids provides the hippopotamus with essential protective functions. The first is natural UV protection, a necessity for an animal that must leave the water to graze. The pigments are effective sunscreens because they absorb light across a broad range of the ultraviolet spectrum. This absorption prevents harmful UV radiation from penetrating the hippo’s sensitive skin, which is prone to cracking and severe sunburn if it stays dry for too long.
The second protective function is the substance’s potent antimicrobial properties. Hipposudoric acid inhibits the growth of several species of pathogenic bacteria, acting as an effective natural antibiotic. The highly acidic nature of the compounds contributes to this effect, controlling microbial populations on the skin’s surface. This is important because hippos frequently sustain deep gashes during territorial battles while living in bacteria-rich water. The continuous secretion of this acidic layer helps to keep wounds clean and prevents serious infections.