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Hives, also known as urticaria, is a medical condition which is characterized by raised, red, often itchy circles of various size that appear and disappear on the skin. They are localized superficially. Urticaria is also known as nettle rash or uredo.

These red skin patches can range in diameter, they often have a pale border and are causing a severe itchy sensation. They usually appear as a result of the body's adverse reaction to certain allergens or for unknown reasons.
Angioedema is a tissue swelling similar to urticaria, but the swelling occurs beneath the skin instead on the surface. It is a much more serious condition. Angioedema is characterized by deep swelling around the eyes and lips and sometimes of the genitals, hands and feet. Angioedema generally lasts longer than urticaria, but the swelling usually goes away in less than 24 hours. This can be a very dangerous condition because, angioedema of the throat, tongue or the lungs can block the airways, causing difficulty breathing and become life-threatening even though this happens really rarely.

Incidence

Urticaria affects 15-20% of the general population in the US and around the world. One in five people is experiencing acute hives or angioedema at some time of their life. Hereditary angioedema affects only about 6,000 people in the United States. Incidence rates for acute urticaria are similar for men and women although the chronic urticaria occurs more frequently in women.

Types of urticaria and angioedema

Acute Urticaria

This type of hives lasts less than six weeks. The most common causes are
  

  • food
  • medications
  • latex
  • infections
  • environmental factors (pollens, chemicals, plants, dander, dust, mold)
  • emotional stress
  • insect bites and
  • some internal disease


The most common food that can cause hives includes nuts, chocolate, fish, tomatoes, eggs, fresh berries and milk.

Among the most common medications that can cause hives and angioedema are:
 

  • Aspirin
  • Nonsteroidal anti-inflammatory medications
  • Ibuprofen, high blood pressure medications (ACE inhibitors) or
  • Pain-killers such as codeine


Chronic Urticaria and Angioedema
 
Hives that are lasting more than six weeks are called the chronic ones.
The cause of this type of hives is usually more difficult to identify than that of the acute urticaria and the fact is that it remains unknown in more than 80 percent of patients. Chronic urticaria and angioedema can effect internal organs and can cause symptoms such as shortness of breath, vomiting, and diarrhea. They can also be caused by several other conditions such as:
 

  • emotional stress
  • heat
  • exercise
  • chronic medical illness, such as hyperthyroidism, SLE, rheumatoid arthritis
  • pregnancy



Physical Urticaria

This is the type of hives caused by the direct physical stimulation of the skin such as cold, heat, sun exposure, vibration, pressure, sweating, exercise and others. Most of the experts believe that there is a completely different mechanism behind this type of urticaria. The hives usually occur at the site of direct stimulation and rarely, appear on other skin areas. Most of the hives appear within one hour after the exposure. There are several sub-types of this urticaria and the most common are:
 

  • Aquagenic: Reaction to water
  • Cholinergic: Reaction to body heat
  • Cold: Reaction to cold, such as ice, cold air or water
  • Delayed Pressure: Reaction to standing for long periods, bra-straps, belts
  • Heat: Reaction to hot food or objects
  • Solar: Reaction to direct sunlight
  • Vibration: Reaction to vibration
  • Adrenergic: Reaction to adrenaline 


Dermatographism

This is a very common type of urticaria and most of the experts count it into physical urticaria group. Anyone can experience this sometimes in life because this type of hives is considered a normal variant of the skin. This type of hives form after firmly stroking or scratching the skin.  
      
 

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