Various types of urticaria, hives, urticarea, or nettle rash :
Acute urticaria usually show up a few minutes after contact with the allergen and can last a few hours to several weeks. Food allergic reactions typically fit in this category. Common causes of reaction include consumption of shell fish, nuts, eggs, fish, acid derivitives, dye.
Chronic urticaria refers to hives that persists for 6 weeks or more. There are no visual differences between acute and chronic urticaria. Some of the more severe chronic cases have lasted more than 20 years.
Drug-induced urticaria has been known to result in severe cardiorespiratory failure. The anti-diabetic sulphonylurea glimepiride (trade name Amaryl?), in particular, has been documented to induce allergic reactions manifesting as urticaria.
Other cases include aspirin, penicillin, sulfonamides and anticonvulsants.
Physical urticarias is often categorized into the following.
Aquagenic: Reaction to water (rare)
Cholinergic: Reaction to body heat, such as when exercising or after a hot shower
Cold: Reaction to cold, such as ice, cold air or water
Delayed Pressure: Reaction to standing for long periods, bra-straps, belts
Dermatographism: Reaction when skin is scratched (very common)
Heat: Reaction to hot food or objects (rare)
Solar: Reaction to direct sunlight (rare)
Vibration: Reaction to vibration (rare)
Adrenergic: Reaction to adrenaline / noradrenaline (extremely rare)