from what i understand, its covered in hairs and each hair has an acid like substance. so i guess the hair is still in your skin. to get the hair out for polyester, i use poster tack, seems to work, not sure if its the same for nettles. there might be a way to calm down the itch. i use sarna sensitive which works well. gloves and a long sleeve jacket should be enough. but this is what the gardeners are for, they may be worth the price.
i don't think it spreads, but there might be a delayed reaction. and the histamines generated through the scratching may make it worse. i'm betting a cool soak should help.
---Mike Savad