Urticaria occurs when the body reacts to an allergen and releases histamine and other chemicals from under the surface of the skin.
The histamine and chemicals cause inflammation and fluid to accumulate under the skin, causing wheals.
Examples of known triggers include:
- medications, including some antibiotics and non-steroidal anti-inflammatory drugs(NSAIDs), such as aspirin and ACE inhibitors, used for high blood pressure
- foods, such nuts, shellfish, food additives, eggs, strawberries, and wheat products
- infections, including influenza, the common cold, glandular fever, and hepatitis B
- bacterial infections, including urinary tract infections and strep throat
- intestinal parasites
- extreme temperatures or changes in temperature
- high body temperature
- pet dander from dogs, cats, horses, and so on
- dust mites
- cockroaches and cockroach waste
- some plants, including nettles, poison ivy, and poison oak
- insect bites and stings
- some chemicals
- chronic illness, such as thyroid disease or lupus
- sunlight exposure
- water on the skin
In over half of all cases, people never find the exact cause.
Chronic urticaria may start as an autoimmune response, but why it happens is unclear.
Swellings, known as wheals, appear as a rash on the skin. They are usually pink or red, with an oval or round shape. They can range from a few millimeters to several inches across. They can be extremely itchy, and they have a red flare around them.
The wheals usually occur in batches, frequently on the face or the extremities, including the arms, hands, fingers, legs, feet, and toes.
Welts normally disappear within 24 hours, but new ones may form. They can appear on just one part of the body, or on several parts.
Symptoms normally disappear within 24 hours, but sometimes another weal appears as the last one fades.
In some cases, hives can continue for several days. People with chronic hives can have symptoms for months or years.
Hives, or urticaria, can be acute or chronic.
Acute urticaria is the most common type. Symptoms last less than 6 weeks, and they typically affect the face and neck, fingers, toes, and the genitals of males. However, any part of the body can be affected.
Chronic urticaria continues for more than 6 weeks. About 1 in every 1,000 people is estimated to experience chronic urticaria.
The exact cause is unknown, but it may link to the immune system. Viruses can also trigger hives. In some cases, it may relate to an underlying autoimmune disorder, such as thyroid disease or lupus.
Angioedema may also occur. This is similar to hives, but it affects the deeper layers of the skin.
Diagnosis will depend on the type of urticaria.
In acute urticaria, allergy testing can help to find a specific substance or trigger for the hives reaction.
A health professional can diagnose acute urticaria by examining the rash on the skin.
Pinpointing the trigger can help the patient prevent recurrences.
The doctor will probably ask about:
- when and where the episode began
- whether there has been an insect bite
- whether the patient lives or works in a place where potential triggers may exist, such as latex gloves, chemicals, or animals
- any medications the patient has been taking, including herbal supplements
- the patient’s medical history
- any family history of urticaria
Often, the trigger is unclear, but if there appears to be a specific trigger, the doctor may refer the patient to an allergy clinic.
Allergy clinics test the patient’s blood and skin to find out whether there is an allergy to specific substances, such as chemicals, dust mites, or some food.
If the urticaria continues for more than 6 weeks, the trigger is probably not external, so experts do not recommend allergy tests at this point.
The following tests can check for underlying health conditions:
- blood test to check for anemia
- stool sample to identify any parasites
- erythrocyte sedimentation rate (ESR) test, to identify problems with the immune system
- thyroid function test to assess for an overactive thyroid, known as hyperthyroidism, or hypothyroidism, an underactive thyroid
- liver function tests, in case there are liver problems
Factors that may worsen the existing urticaria include:
- caffeine intake
- mental health issues, such as stress
Antihistamines treat acute hives, but antibiotics may be needed for chronic hives.
Treatment for acute urticaria includes non-sedating antihistamines taken regularly for several weeks.
Antihistamines, such as cetirizine or fexofenadine, help by blocking the effects of histamines and reducing the rash and stopping the itching.
Various antihistamines can be purchased in pharmacies or online.
Some antihistamines cause drowsiness, especially if the user also consumes alcohol. Some are not suitable during pregnancy unless prescribed by a doctor.
Patients with angioedema may need to see an allergist, an immunologist, or a dermatologist. Angioedema can cause potentially serious breathing difficulties.
If there is swelling of the tongue or lips, or if breathing becomes difficult, the doctor may prescribe an epinephrine auto-injector, for example, EpiPen, in case of emergencies.
Patients should avoid known triggers, if possible.
Chronic urticaria can cause long-term discomfort, and sometimes complications can occur.
Treatment is different than that for acute urticaria.
Antibiotics, for example, Dapsone, can reduce redness and swelling.
Omalizumab, or Xolair, is an injectable drug that blocks immunoglobin E, a substance that plays a role in allergic responses. It can reduce symptoms of chronic idiopathic urticaria, a type of hives of unknown origin that can last for months or years.