Cheilitis caused by contact urticaria to mint flavoured toothpaste. 
A 26-year-old woman presented with a 12-month history of persistent dermatitis of the lips.  She had failed to respond to cosmetic avoidance and therapeutic measures.  Patch testing was negative, including her toothpaste and toothpaste flavours.  She defied diagnosis until an acute flare followed immediately after dental treatment with a mint flavoured tooth cleaning powder.  This led us to prick test her to mint leaves and this was positive.  Her cheilitis settled after changing from her mint-flavoured toothpaste.  A diagnosis of contact urticaria should be considered in cases of cheilitis of unknown cause.