Chronic hives may be spontaneous or inducible (physical). You can have both types at the same time.
Spontaneous chronic urticaria is the diagnosis when the trigger for hives is not known.
Inducible or physical chronic urticaria is a reaction to a known external factor. This includes hives caused by the following:
- stroking your skin (dermographism) – this is the most common type of inducible/physical urticaria
- exposure to cold, cold water and cold objects (cold urticaria)
- sweating (cholinergic urticaria)
- direct contact with a substance such as stinging nettles, foods, preservatives, fragrances, plant and animal products, metals and rubber latex (contact urticaria) – this is different to dermatitis, which develops hours or days later
- pressure to your skin – this can be an immediate or delayed reaction (pressure/delayed pressure urticaria)
- exposure to sunlight or to artificial ultraviolet (UV) light (solar urticaria)
- direct contact of warmth to your skin (heat urticaria)
- exposing your skin to vibration, repetitive stretching or rubbing (vibratory urticaria)
- contact with water (aquagenic urticaria).
Some of these types are quite rare.