The internet has long been buzzing with a curious rumor: that hippopotamus milk is pink. This notion gained momentum when National Geographic shared it on their Facebook page. However, the truth is far less colorful—hippo milk is actually white or cream in hue.
Rebecca Lewison, a biology professor at San Diego State University and co-chair of the IUCN SSC Hippo Specialist Group, debunked the myth, affirming, “I have never heard their milk is pink, so that is a rumor.” Lewison clarified that while hippo “sweat” does indeed appear pink, it’s not actually sweat but a skin secretion packed with sunscreen and antibiotic properties.
This so-called “sweat” is produced by the animal’s mucous glands and is composed of hipposudoric acid and nor-hipposudoric acid, pigments that offer protection against harmful bacteria and UV radiation.
Lewison explained that this secretion serves multiple functions, including moisturizing the skin, cooling the animal, and preventing infections, particularly crucial for hippos that spend extensive hours submerged in muddy waters. Despite sustaining scratches and cuts, hippos exhibit remarkable wound healing facilitated by this secretion.
While the initial secretion is colorless, exposure to sunlight causes it to polymerize, resulting in hues ranging from red to pink to orange before ultimately turning brown.
Speculating on the origin of the pink milk myth, Lewison proposed that the secretion might mix with the milk when a baby hippo is nursing, potentially tinting it pink.
However, Barbara Henry, curator of nutrition at Cincinnati Zoo and Botanical Garden, warned that pink milk could indicate a health issue, suggesting that any pink hue in hippo milk might signal the presence of blood, rather than natural pigmentation.