The development of hives can occur at any time.  The causes of hives can be varied and depends on the duration of the symptoms.  Patients with hives that last less than six weeks are labeled acute urticaria.  Patients with hives lasting longer than six weeks are labeled chronic urticaria.  Some patients may have swelling associated with urticaria.

What causes urticaria?

Acute urticaria (hives that last less than 6 weeks)

There are numerous causes for why someone may present with acute urticaria.  The most common known causes include foods, medications, insect stings, blood transfusions, contact allergies and infections.  However, in some cases a clear cause is not found.

Chronic urticaria (hives that last longer than 6 weeks)

The causes for chronic urticaria are often more difficult to identify.  In these patients, the cause may not be an external trigger but rather an internal mechanism that is causing the patient to develop hives.  Many of these patient are eventually labeled as idiopathic but this is a diagnosis of exclusion.  Up to 40% of the patients that are labeled as idiopathic may have a form of autoimmune urticaria.  Some patient's may have a physical urticaria.  The most common form of physical urticaria is termed dermatographism.  Other forms of physical urticaria can be associated with cold exposure, exercise, and pressure among others.

How is it diagnosed?

Patient's that suspect they have urticaria may want to keep some notes on the frequency of the hives (individual lesions come and go and do not usually leave changes on the skin), the duration (individual lesions do not usually last longer than 24-36 hours; circling a lesions may help a patient keep track of this), whether there is swelling associated, if there are any foods that seem to be associated with the onset of the hives, medications or supplements the patient is taking (prescription, herbal, over-the-counter), and any recent infections or other symptoms associated with the hives.

The doctor will perform a history and a physical and may want to run a few tests such as blood tests or skin tests to help identify a cause for the hives.

How is it treated?

Oral antihistamines are usually considered first when treating urticaria.  Many over-the-counter medications, however, can be associated with side effects such as sleepiness or dry mouth; symptoms which may be bothersome to the patient.  There are a number of medications that a doctor may consider using to treat a patient depending on the type and severity of urticaria the patient may have.  In some cases, a combination of medications may be needed to get the patient's symptoms under control.  In difficult to treat patients, oral steroids or immunosuppressive medications may be needed. Which medications should be used will depend on the patient's ability to tolerate the medication, their response to the medication, and there comfort level with taking medication regularly.

What is the prognosis?

The type of urticaria that a patient has will help determine the prognosis.  If the cause for acute urticaria is known then treatment or avoidance of the trigger will often improve the patient's symptoms.  For those patient's with chronic urticaria the prognosis depends on the type of urticaria they have.

If a patient has symptoms consistent with urticaria they should see a doctor to discuss the appropriate tests and treatment.