(Scroll down for Swahili translation)

Hippos have naked skin which is an adaptation to spending so much time in the water. The outer layer of their skin is actually very thin and sensitive and scratches and bleeds easily. The layer underneath is quite thick and up to 6cm in places. A hippo’s skin makes up about 18% of its weight and the function is to keep them warm in the water but at the same time offers a challenge of keeping cool, which is why hippos are usually active at night.

The answer to this question of hippo sweat is really a technicality. Before I answer the question, I think it is important to make sure that we have a good understanding of what sweat is and what type of glands it comes from.

Humans sweat more than any other animal in the world (relative to our size), but we produce two types of sweat. One is a fairly simple mixture of salt and water that is meant to evaporate and thus cool our bodies when we are overheating. These come from glands called eccrine glands and more are found in human’s skin than in other animals. The other type of sweat is produced in our armpits and groin and contains other chemicals like pheremones. These come from apocrine glands that are associated with the hair. This type of sweat is produced by other animals too and contains chemical signals but can also help to cool the body.  We also have a third type of gland in our skin called sebaceous glands. These glands also produce oils that are important for skin and hair health. These glands are in the second layer of skin called the dermis.

The reason the pink liquid that hippos produce is not called sweat is because it doesn’t come from the sweat glands we described above. Instead the liquid is produced by glands that are under the dermis (this is the answer). The secretion is alkaline and has a pH of 8.5-10.5 and contains two pigments- a red one and an orange one. These secretions have antiseptic, anti-fungal, and sunscreen properties.

If you want to know why hippos don’t sweat, well the reality is that most animals don’t sweat. Most animals control their body temperatures by panting and being less active during the hot hours of the day. This is also the answer why lions and other cats pant even if they haven’t been active- they just don’t have the ability to sweat like we do. Humans are actually unique in our ability to sweat from eccrine for the purpose of cooling. If you want to read more about why researchers think this, here are my sources.

Viboko wana ngozi bila nywele. Ni toholeo ya kuishi kwenye maji. Rusu ya nje ni nyembamba na ni nyepesi kukwaruzwa na kutoa damu. Rusu ya pili ni nene na inaweza kufikia unene wa sentimeta 6 sehemu zingine. Ngozi ya koboko ni asilimia 18 ya uzito wake na kazi ya ngozi mmojawapo ni kumhifadhi na baridi akiwemo kwenye maji, lakini vile vile inampa changamoto kujipooza mwili na ndiyo maana kwa kawaida wanatembea usiku.

Jibu la swali kuhusu jasho la kiboko ni la msingi. Kabla sijalijibu ni muhimu kuhakikisha tunaelewa  jasho ni nini na inatokea kwenye tezi ya aina gani.

Binadamu hutoa jasho zaidi kuliko mnyama yoyote mwengine duniani (kulingana na ukubwa wetu), lakini tunatoa aina mbili za jasho. Mmoja ni mchanganyiko wa maji na chumvi yenye kazi ya kuyeyuka na kupunguza joto mwilini wakati tunapata joto kupita kiasi cha kawaida. Jasho la aina hii linatoka kwenye tezi za ‘eccrine’ na zinapatikana kwenye ngozi ya binadamu kwa kiasi kikubwa kuliko wanyama wengine. Aina ya pili ya jasho inatoka kwenye maeneo ya kwapa na linena na linakua na kemekali zaidi kama ‘pheremone’. Hili jasho linatoka kwenye tezi za ‘apocrine’ ambazo pia zina uhusiano na nywele. Baadhi ya wanyama wengine wanatoa jasho la aina hili na linasaidia kupunguza joto lakini vilevile kwenye mawasiliano katikati ya wanyama kwa njia ya kemekali. Sisi tuna aina ya tatu ya tezi kwenye ngozi yetu, aina ya ‘sebaceous’. Hii tezi hutengeneza mafuta muhimu kwa ajili ya afya ya ngozi na nywele yetu. Hizi tezi zipo kwenye rusu ya pili ya ngozi kinachoitwa ‘dermis’.

Sababu ya kutokuiita huo utoaji wa kiboko jasho na kwa sababu haitokei kwenye tezi za jasho tulizozielezea hapo juu. Huo utoaji unatengenzwa na tezi zilizopo chini ya rusu ya ‘dermis’. Huo tezi ni ‘alkali’ (kama magadi) yenye pH ya 8.5-10.5 na ina rangi mbili- mmoja nyekundu na mmoja rangi ya machungwa. Huo utoaji una sifa za kuua bakteri, huzuia kuvu, na kuzuia kuungua na jua.

Kama unataka kujua kwa nini viboko hawatoi jasho, ukweli ni kwamba wanyama wengi hawatoi jasho. Baadhi ya wanyama kudhibiti joto mwilini kwa kutweta (kuhema sana) na kupumzika kipindi cha joto. Hii ndiyo sababu ya wanyama kama simba na paka wengine kutweta wakata wa joto hata kama wamepumzika. Katika wanyama binadamu ni pekee mwenye uwezo wa kutoa jasho kutoka kwenye tezi za eccrine kwa ajili ya kujipooza . Ukipenda kusoma zaidi uzicheki maandiko rejea hapo chini.

The evolution of sweat glands.
G. Edgar Folk, Jr. 1 and Holmes A. Semken, Jr. 2 Dec. 1991. Journal of Biometeorology.

The Red Sweat of the Hippopotamus. Yoko Saikawa, Kimiko Hashimoto et. al. May 2004. Nature.

Mammalian Thermoregulation: Species Differences. N. R. Brewer & Leon J. Cruise. May 2000. CONTEMPORARY TOPICS by the American Association for Laboratory Animal Science

Sweating is an Essential and Uniquely Human Function. Adam Wernick. 2017. PRI.org

The Naked Truth, by Nina Jablonski, November 2012. Scientific American.