A yeast infection is a very common cause of skiny dogs. Yeast has a very pungent, musty, unique odor that has been complared to modldy bread, cheese popcorn, or corn chips. Some people actually refer to a yeast infection on a dog's paws as "Frito Feet".
Stinky paws or musty-smelling ears are usually a sign of yeast overgrowth. So is scratching. Itchy ears, itchy paws and butt scooting are all signs of a potential with yeast.