You are also a big object hurdling through space, being bombarded with anything else that is occupying that space. Like bugs for instance. It's a simple formula really...
(Bugs + sweat) x miles per hour = HOT MESS
If you need that shot in a bit more detail...yes Virginia, those are bugs. The kids were completely grossed out.
Also, in other news Ironman race officials are looking at alternative places to hold the swim. Read more here.