Dermatographic urticaria. An<unk>  is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune<unk>  in everyone. An<unk>  may cause harmful symptoms such as itching or inflammation or tissue injury.
Allergic response
Central tolerance
Neural adaptation
Sensitization 
Peripheral tolerance
Desensitization 
Cross-tolerance
Neural facilitation