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If it happens to you:
Pay attention to the signs. If you get an immediate swell in your mouth, have trouble breathing, then you should immediately go to the hospital in case you are allergic.
If the swelling is mild, then 👇

First make sure that the sting is (gently) removed.
Clean the area & put some cold water or an ice cube on it.
There are special creams for bee stings, I have not used them but If you have, apply.
You should be fine a few hours afterwards.