Flick through a fashion magazine this summer and you'll be bombarded with adverts warning against sunburn. In an era of ozone depletion and heightened awareness of skin cancers, many retailers are earning good PR points by stocking only high-factor sunscreen products; complementing their ranges with a multitude of celebrity-endorsed fake tanning lotions and potions. But with millions of pounds already invested in developing the next generation of sunscreen sprays, industry insiders may be more than a little surprised to hear that hippos, not humans, are leading the way in today's most sophisticated sun protection.

A recent study by Yoko Saikawa and his team at Keio University and Kyoto Pharmaceutical University in Japan has revealed that hippos produce their own coolant, antibiotic and sunscreen all in one. Chemical analysis of the pigments responsible for the famous hippo blush has solved the mystery behind the ancient myth that hippos sweat blood.

Produced by the glands under the skin, and therefore not strictlya sweat, hot hippos secrete a fluid that acts like sweat in helping to control body temperature. The massive beasts live in central Africa, mainly in the Nile Valley, where they spend most of the year under direct sunlight and searing heat. Their `sweat' is produced as a thick clear fluid but turns red-brown within a few minutes of perspiration. This change in colour creates the famous hippo flush over the face, behind the ears and down the back.

Noticing that the animals produce more of this sticky substance when lazing on land than in water, scientists began to wonder if the secretion might have other benefits. Eager to discover more about the colourful liquid, Saikawa's team bravely wiped the brows and backs of two captive hippos to collect samples on gauze swabs. The researchers then extracted the chemicals from the liquid, concentrated and purified them, and ultimately isolated two pigments -one red and one orange. Naming the red pigment `hipposudoric acid' and the orange pigment `norhipposudoric acid', the researchers then set out to test the potential antibiotic and sunscreen properties of the fluid.

By trying to grow bacteria in the presence of the pigments, the scientists discovered that the red pigment acts as an effective antibiotic. Male hippos are renowned for their aggressive clashes with rivals, and antibiotic secretions may play an important role in minimising battle-won infections.

Satisfied at having solved one mystery, the researchers then turned their attention to the potential sun screening function of the `sweat'. By measuring how much of the sun's spectrum is absorbed by the secreted pigments, Saikawa and colleagues revealed that the fluid blocks a good portion of the ultraviolet and visible spectrum (200-600 nm). The researchers conclude that hippo sweat cools the body and protects against both infection and sunburn. Not bad for an ancient lumbering beast.

Having unlocked the secrets of the multipurpose hippo flush, scientists may now focus their attention on discovering how the famous red-brown hue is maintained for hours after secretion. Multipurpose and long lasting - this hippo product appears to have it all.

Saikawa, Y., Hashimoto, K., Nakata, M., Yoshihara, M., Nagai,K., Ida, M. and Komiya, T. (
). The red sweat of the hippopotamus.