How long can hives last?
Hives can last a variable amount of time. Usually, eruptions may last for a few minutes, sometimes several hours, and even several weeks to months. Most individual hives last no more than 24 hours.
What are the different types of hives?
Acute episodes of urticaria last for six weeks or less. Acute urticaria can be due to infections foods, medications, insect stings, blood transfusions and infections. The most common cause of hives is infections. Foods such as eggs, nuts and shellfish are common causes of urticaria. Medications such as aspirin and antibiotics (especially penicillin and sulfa) also are common causes of hives. Infections causing hives include the common cold, and other viral infections. In most of these cases, when the reason for hives is removed or avoided, the hives resolve.
Chronic episodes of urticaria last more than six weeks. In most cases, the cause of chronic hives will not be identified despite testing. Half of the patients have antibodies (proteins) that attack the mast cell (allergy cell). This triggers chemicals such as histamine to be released which causes the hives and itching. Even though hives are associated with other autoimmune conditions such as thyroid disease, treating the other condition doesn't cure the hives. Rarely, chronic urticaria has been associated with cancer. In most cases of chronic urticaria, the hives will gradually disappear over time.
Physical urticaria is due to one or more 'physical' causes. The most common reason for long-lasting hives is dermographism. These hives appear within a few minutes of scratching along an area of skin. Most often, the rash is linear, following the path taken by the act of scratching. Delayed pressure urticaria is swelling that appears on areas of constant pressure from belts and constricting clothing such as sock bands. Cold urticaria (from exposure to low temperature followed by re-warming) can be severe and life threatening if there is a generalized body cooling, for example after a plunge into a swimming pool. Cholinergic urticaria is due to an increase in body temperature with sweating, exercise, hot showers, and/or anxiety. Sun-induced urticaria may occur within a few minutes after exposure to the sun.
What causes hives?
In some cases, the cause is clear. A person ingests nuts or fish, and then develops hives within a few minutes or possibly a couple of hours. Some cases require a more detailed history from an Allergist to help figure out the cause. A single episode of uncomplicated hives does not usually need extensive testing. If the reaction involves respiratory symptoms, such as coughing, shortness of breath, throat closing or tongue swelling, then the patient should be immediately brought to the emergency department. If allergy is suspected, a diary of foods eaten within a few hours before the hives started may be extremely helpful.
Chronic urticaria should be evaluated by an Allergist/Immunologist. This specialist will take a detailed personal medical history, familys' medical history, and medication history. In some cases you may require tests to analyze blood and urine. It is rare for a food to cause chronic hives. The specific cause of hives is rarely identified.
What medications treat hives?
There are many different antihistamines that are used to treat hives. Some cause drowsiness, others don't. Very commonly patients are given a few antihistamines at a time to treat the hives. Sometimes medications such as steroids, antileukotrienes, and cyclosporine are needed to control hives.
Importance of medical follow-up
Whatever medication is used does not cure the hives, but helps to control outbreaks. When the medications are discontinued the hives can return. Patients should have us monitor their progress every one to two months initially.
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