Types of Urticaria

Urticaria is a skin rash.  It is sometimes called hives, or nettle rash, and it is accompanied by swellings and itchiness of the skin.  The rash consists of anything from one to countless wheals, each of which may be anything from a half centimetre to many centimetres in diameter.  Each weal is an itchy, raised area of skin that is reddened around the edge, but often paler in the middle.  

It occurs when cells near to the surface of the skin are stimulated to release histamine.  This chemical substance is involved in the body's normal defence mechanism, and when it is released inappropriately it produces the symptoms we commonly associate with allergy.  If released in the nose, we get the symptoms of hay fever, if released in the lung, we get the symptoms of asthma and if released in the skin, we get urticaria.  The hairs on the surface of a nettle leaf contain histamine, and this is why the rash is similar to what happens when we are stung by nettles.

The wheals of urticaria whiten if pressure is applied to the rash. The rash generally disappears within a few hours, although in some cases, crops of wheals continue to appear for days or even months.  

Urticaria is described by the length of time that symptoms last.  If there is just a single attack and it lasts less than six weeks it is called acute urticaria.  When episodes last more than six weeks the condition is described as chronic urticaria.  When it has been shown that an allergy triggers an attack, the condition is called allergic urticaria.  When it has been shown that pressure, scratching, cold, heat, exercise or sunlight exposure triggers an attack the condition is called physical urticaria.   

Acute Urticaria

Single and isolated attacks of urticaria are known as acute urticaria.  This is not an uncommon condition, particularly in children.  The rash that develops can be quite dramatic and alarming.  However, it is usually a quite harmless condition.  There is often no obvious cause; the explanation considered most likely is that a quirk of the body's immune defence mechanism has caused the rash in the process of fighting off a common and harmless infection.  This is not the same a saying that the rash is infectious; it is not.

When people who experience infrequent attacks of acute urticaria are investigated, allergic causes are occasionally found.  When allergy is the cause, the urticaria is more commonly of the chronic variety (recurrent or persistent attacks).   

Chronic Urticaria

Chronic urticaria is an episode, or a series of recurrent episodes, of urticaria that last more than six weeks.  Sometimes it may happen when short attacks of urticaria keep occurring and sometimes it may happen when an attack starts and then continues all the time, sometimes without a break.

As with acute urticaria, there may be allergic causes and there may be physical causes.  It is possible that in some cases that both of these causes may play a part.