How long will it take to go away?

Ok, basically, I've been very stupid. This isn't a joke thread, although I'm very well aware it may sound like it.

Yesterday, I was messing with the flippy switch thing on the top of my inhaler, and it trapped my lip. It rather hurt, quite a bit, and whilst I eventually managed to get it off, I've been left with a bright red rectangular-shaped mark on my lip, as well as a learnt lesson to never do it again.

How long will this mark take to go away???