The phrase “pink milk” often surfaces when discussing hippos, highlighting a common misconception about these large, semi-aquatic mammals. This article explores the scientific realities behind the hippo’s distinctive appearance, moving beyond popular myths to uncover the true nature of its specialized skin secretions.
Unraveling the ‘Pink Milk’ Myth
Despite the common rumor, hippos do not produce pink milk. Like all mammals, a female hippo’s milk is typically white or cream-colored, providing nourishment for their young. The confusion arises from a unique, oily secretion that covers the hippo’s skin, often mistakenly referred to as “blood sweat” due to its reddish-orange hue.
This specialized substance is neither blood nor true sweat, as hippos lack typical sweat glands. Instead, it originates from subdermal glands, which secrete a viscous, colorless fluid.
The Unique Pigments Responsible
The distinctive color of the hippo’s skin secretion comes from two unique acidic pigments: hipposudoric acid, which gives a reddish-orange shade, and norhipposudoric acid, contributing an orange or red color. These compounds are unique to hippos and are believed to be synthesized from common precursors, such as amino acids like tryptophan or homogentisic acid. The secretion initially appears colorless when exuded, but quickly oxidizes upon contact with air and sunlight, developing its characteristic reddish-pink to brownish hue. Over time, these pigments can polymerize, causing the secretion to darken further, eventually turning brown.
Protective Properties of Hippo Sweat
The unique skin secretion of the hippopotamus serves multiple protective functions for the animal’s sensitive skin. Primarily, it acts as a natural sunscreen, absorbing harmful ultraviolet (UV) radiation across a broad spectrum, typically between 200 to 600 nanometers. This built-in UV protection is important for hippos, whose nearly hairless skin is prone to sunburn and drying when exposed to intense sunlight.
Beyond sun protection, the secretion also possesses antiseptic and antibiotic properties. Hipposudoric acid, in particular, inhibits the growth of various pathogenic bacteria, even at low concentrations. This antimicrobial action helps prevent infections from wounds and abrasions, which are common for hippos living in muddy, aquatic environments and engaging in territorial conflicts. Additionally, the oily nature of the secretion acts as a moisturizer, helping to keep the hippo’s skin hydrated and preventing it from cracking or becoming waterlogged.