What large animal sweats the color red?
Yes, Hippopotamus actually make their own form of sunscreen through their sweat! Shortly after a hippo begins to perspire, its sweat turns to red due to oily red ("hipposudoric acid") and orange ("norhipposudoric acid") pigments that are being secreted.
The sweat takes on the appearance of blood, so if someone didn't know better, they may think the enormous animal is actually injured! Certain molecules within the pigments have been shown to absorb UV rays, working as a form of natural sunscreen.
The sweat is also found to be acidic in nature and in particular the red pigment has been discovered to be a rather good antibiotic, allowing the hippo to accelerate it's healing process and protect itself from certain harmful pathogens. The sweat first appears colorless, shortly after turning to red, then finally brown as the pigments polymerize.