All types of Vinegar help to neutralise wasp stings. If you are allergic to wasps then seek medical attention.
DYC White Vinegar
Check to see if there is a sting left behind by the wasp (usually wasps dont leave a sting behind). Remove with tweezers.
Soak a cotton ball with vinegar and press on the area for around 10 minutes.
To help reduce swelling apply ice pack to the area.