pimple, sore, boil, wart, pustule
疙 centers on skin blemishes and raised lesions: pimples, sores, boils, warts, and pustules. All meanings are specific types of skin eruptions.
疙 combines 疒 (sickness) with 乞, which likely contributes a phonetic element. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to skin ailments.
The sickness enclosure 疒 wraps around 乞, like a raised bump on the skin. Picture a person begging (乞) for relief from an itchy, swollen pimple.
For ギツ, imagine a giant pimple that makes a sharp 'gitsu!' sound when it pops: gitsu -> ギツ, and the sore is gone.