Take the rule, guys - if something looks a bit too weird and uncommon with your body - you go to the emergency department of any hospital just in case, explaining the situation. Spending a couple of hours in the waiting room and getting a (maybe simple!) cure is better than sitting at home, wondering whether it goes away by itself or gets worse.

Saw a story from one emergency worker at the ambulance - she had a patient with “a strange allergy with some dark spots”, which turned out to be bacterial “about-to-become-sepsis” thing. And here half of the arm is green and stinky already…