Well, I had to look up the word "asperity" so that should tell you it's not too idiomatic or common.
"of the flesh" "in the body" sound archaic and Biblical/Shakespearean, the English of centuries ago. Not too common.
Do you mean something like "He's got chickenpox, so he hurts all over" ?
(
his body is understood, so is not said in this set phrase idiom: "I fell, and now I hurt all over."
Do you mean as a separate matter that he's got rough patches on his skin due to the chickenpox, but you saw that "asperity" was given a dictionary synonym of
rough?
If so, that kind of
rough means
difficult to accomplish/severe in manner.
But
rough has another quite different meaning of "
not smooth in texture/feels scratchy when you touch it." A cat's whiskers, hair stubble on the skin, a brick, are some examples.
So, now that you know there's a difference, other posters and I might be able to offer better suggestions when we know what you're trying to say. I'm not quite sure yet.