Urticaria (from the Latin
urtica,
nettle (whence It. ortica, Sp. ortiga, Pg. urtiga)
urere, to burn
[1]) (or
hives) are a kind of skin rash notable for dark red, raised, itchy bumps. Hives are frequently caused by allergic reactions; however, there are many non-allergic causes. For example, most cases of hives lasting less than six weeks (acute urticaria) are the result of an allergic trigger. Chronic urticaria (hives lasting longer than six weeks) are rarely due to an allergy. The majority of patients with chronic hives have an unknown (
idiopathic) cause. Perhaps as many as 30-40% of patients with chronic idiopathic urticaria will, in fact, have an autoimmune cause. Acute viral infection is another common cause of acute urticaria (viral
exanthem). Less common causes of hives include friction, pressure, temperature extremes, exercise, and sunlight. It may be true that hives are more common in those with fair skin.
Wheals (raised areas surrounded by a red base) from urticaria can appear anywhere on the surface of the skin. Whether the trigger is allergic or non-allergic, there is a complex release of inflammatory mediators, including
histamine from cutaneous
mast cells, resulting in fluid leakage from superficial blood vessels. Wheals may be pinpoint in size, or several inches in diameter.
- 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 often fit in this category. The most common food allergies in adults are shellfish and nuts. The most common food allergies in children are shellfish, nuts, peanuts, eggs, wheat, and soy. It is uncommon for patients to have more than 2 true food allergies. A less common cause is exposure to certain bacteria, such as streptococcus or possibly Helicobacter pylori. [9] In these cases, the hives may be exacerbated by other factors, such as those listed under Physical Urticarias below.
- 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. A survey indicated that chronic urticaria lasted a year or more in more than 50% of sufferers and 20 years or more in 20% of them. Of course this does mean that in almost half the people it clears up within a year and in 80% it clears up within 20 years or less.[10]
- 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 dextroamphetamine[11], aspirin, penicillin, clotrimazole, sulfonamides and anticonvulsants.
Chronic urticaria can be difficult to treat. There are no guaranteed treatments or means of controlling attacks, and some sub-populations are treatment-resistant, with medications spontaneously losing their effectiveness and requiring new medications to control attacks. It can be difficult to determine appropriate medications since some, such as
loratadine, require a day or two to build up to effective levels, and since the condition is intermittent and outbreaks typically clear up without any treatment.
Most treatment plans for urticaria involve being aware of one's triggers, but this can be difficult since there are several different forms of urticaria and people often exhibit more than one type. Also, since symptoms are often
idiopathic (unknown reason) there might not be any clear trigger. If one's triggers can be identified then outbreaks can often be managed by limiting one's exposure to these situations.
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Originally Posted by Emzs
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