Elaine Morgan couldn't quite work out an aquatic angle of sweat, since critics of WWHEs have pointed out that horses also sweat.
I recently watched one of David Attenborough's Natural Curiosities episode, where he relayed how hippos, a semiaquatic mammal from the same region as early hominins, sweat a sticky red substance. According to Japanese scientists (see link above), this acts both as the hippos' own sunscreen, while also having antibacterial characteristics.
"They found it is made up of two pigments - one red, called 'hipposudoric acid'; and the other orange, called 'norhipposudoric acid'.
"Both pigments act as sun blocks and the red one, they discovered, is a particularly good antibiotic."
So can it be as simple as that? That it's a method to avoid sunburns and inflammation also for hominins? Are similar molecules present in human sweat, while not in horses' sweat?