Change in colour of skin can happen after an 'allergic' reaction - due to release of various mediators that happens in an acute allergic episode.
Was this after a drug you had taken?
If so, you must ensure there are no other rashes elsewhere in the body and no oral ulcers as this is a serious adverse drug reaction
and you need to stop all medications if you are unsure what caused it.
If this was a random event, then take antihistamines for a period of 7 days (cetirizine
) even though the swelling has largely gone. Continue to apply the lip balm and the colour of the lips will return.