[1][2] The condition manifests as an allergic-like reaction, causing a warm red wheal to appear on the skin.

The first outbreak of urticaria can lead to other reactions on body parts not directly stimulated, scraped, or scratched.

If the membrane that surrounds the mast cells is too weak, it will easily and rapidly break down under physical pressure, which then causes an allergic-like reaction.

This condition is diagnosed by a health care provider drawing a tongue depressor or other implement across the patient's skin to see whether a red wheal appears soon afterwards.

[8][further explanation needed] While cromoglycate, which prevents histamine from being released from mast cells, is used topically in rhinitis and asthma, it is not effective orally for treating chronic urticaria.