The Hippopotamus’s ‘Blood Sweat’: A Natural Sunscreen and More

The hippopotamus, one of the largest land mammals, faces intense sun exposure in its sub-Saharan African habitat. To combat this, it produces a unique, reddish secretion often called “blood sweat.” But what exactly is this substance, and what purpose does it serve?

Naturally Protected Skin

Hippos spend much of their day in water, but emerge at night to graze. Their skin, though thick, is nearly hairless, leaving them vulnerable to the sun’s harmful ultraviolet (UV) rays. However, hippos possess a natural defense mechanism: they secrete a protective substance that forms a thin film over their skin, filtering UV radiation – essentially acting as a natural sunscreen.

Other animals employ different strategies. Elephants, for example, utilize mud baths to shield themselves from sunburn and regulate their body temperature.

A Liquid That Replaces Sweat

Unlike many mammals, hippos lack functional sweat glands. This means they can’t cool down through perspiration. While they maintain a stable temperature while submerged in water, they risk overheating on land. This is where “blood sweat” comes into play, acting as a thermal regulator and keeping their skin hydrated.

A Natural Antiseptic

The secretion as well possesses antiseptic properties, helping to prevent infections. This is particularly important given the hippopotamus’s frequent exposure to bacteria and pathogens in often-contaminated water sources. It also aids in wound healing, protecting against infection from injuries sustained during territorial fights between males, which can involve bites, headbutts, and scratches.

The Composition of ‘Blood Sweat’

The so-called “blood sweat” is composed of two key pigments:

• Hipposudoric acid: This pigment gives the secretion its bright red color.
• Norhipposudoric acid: This pigment contributes an orange tint.

Initially nearly transparent, the liquid quickly turns reddish-orange upon exposure to air and slightly hardens. It’s secreted by glands located on the back, head, and behind the ears. Contrary to its name, this substance is neither blood nor sweat, but rather a type of mucus.

Other Hippopotamus Specifics

The common hippopotamus (Hippopotamus amphibius) derives its name from the Greek word for “river horse,” reflecting its amphibious lifestyle. They inhabit African rivers and lakes, often appearing to float with only their backs and heads visible. While they spend much of their time in the water, hippos cannot swim and hold their breath for several minutes by sealing their ears and nostrils.

A smaller species, the pygmy hippopotamus (Choeropsis liberiensis), is native to the forests and swamps of West Africa.

A Formidable Animal

Despite their bulky appearance and herbivorous diet, hippos are incredibly formidable and considered one of the most dangerous animals in Africa. They are highly territorial and can charge at speeds of 35 to 40 km/h (22 to 25 mph). Their powerful jaws can open to 180 degrees, revealing long canine teeth, up to 30 cm (12 inches) in length, capable of inflicting severe damage. Some estimates suggest the risk of fatality from a hippo encounter is higher than from a lion or shark attack.

Conservation Status

Although adult hippos have few natural predators, they face threats from poaching for their meat, fat, and teeth, as well as habitat degradation and the reduction of water sources. Their life expectancy is typically 30 to 40 years.