boil, carbuncle
癰 centers on a severe, localized skin infection: a boil or carbuncle, a painful pus-filled swelling.
癰 combines the sickness radical 疒 with the phonetic component 雝, which likely contributes the sound ヨウ. The character originally referred to a severe swelling or abscess.
The sickness enclosure 疒 wraps around the complex shape 雝, like a painful, swollen boil trapped under the skin.
For ヨウ, imagine a painful boil that makes you yell 'YO!' when touched: YO -> ヨウ, and the sickness enclosure 疒 contains the swelling.