Today, I wish to talk more on the physical classification of Urticaria. The more common physical agents include:
1. Dermatographia
– “ writing on skin”
– in this condition there is an increased tendency for wheal and flare reactions after mechanical stroking of the skin
2. Cold urticaria
– this could be familial or acquired and maybe induced upon exposure to cold stimulation
3. Cholinergic urticaria
– a condition characterized by multiple wheals which occur after heat exposure, emotional stress or vigorous exercise
– this could be due to histamine release mediated by acetylcholine from cholinergic nerve fibers
4. Solar urticaria
– this urticaria develops after brief exposure to sunlight
5. Pressure urticaria
– there is a gradual onset of deep, painful swelling 4- 6 hours after pressure application to the skin
– this could develop by the use of tight garments like belts, bra straps and or sustained pressure like prolonged sitting position.
