Skinny pigs were first developed in laboratories for experimentation, which probably leaves them a bit genetically susceptible to certain things that they were developed TO test, you know? They were crossed out with Teddy pigs (which explains their wavy hair) I suppose to strengthen the line a bit, but Teddies are also very prone to skin problems and health issues, so it didn't add much in the way of foundation.
Baldwin guinea pigs were developed for show and are completely hairless. They're a mutation sprung up from crested guinea pigs (IIRC) and there's a fair amount of inbreeding that went into them and probably still does due to their small numbers. They're considered "rare and expensive" (like the skinnies) and that draws people to breed more and more of them. They're also born missing a gland, but I can't remember which one off of my head.
Both are prone to abscesses because they don't' have fur and hay is pointy so it sometimes jabs right into their skin. They tend to get skin cancer a LOT because they don't have any systems set up to deal with the amount of sun they're getting and no natural immunity has developed.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry