What's the difference? I got told that 皮膚【ひふ】 only works for mammals (and humans), and 皮【かわ】 for other animals too.
2 Answers
皮膚{ひふ} is generally a formal word for skin, used in academics, clinics etc. (but also frequently in everyday speech).
For example, some fishes do 皮膚{ひふ} 呼吸{こきゅう}. So it's not really for mammals only.
My layman definition is that it has to be on an animal, and doesn't include extra structures like hairs, feathers, scales etc. (but does include the smooth underlying tissue).
皮{かわ} is more colloquial and can refer to any organic, generally thin structure that can be peeled. For example, 木{き}の皮{かわ}.
I agree that 皮膚
is only for mammals, but 皮
does not even have to be of an animal. It can be any kind of skin, those of: fruits, vegetables, wrapped food (dumpling, etc.), etc.