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Urticaria (Nettle Rash)

Between 15-23% of the population would have experienced at one time or other, this condition. And for some 25% of these patients it is a chronic condition. In the majority of cases the acute urticaria reaction will last for a few hours or more, however in chronic urticaria patients, the wheals may last for days or even weeks.

In chronic urticaria the cause is unknown in up to 80% of cases but an intolerance to salicylates and benzoates is a common trigger. This type of urticaria affects mainly adults and occurs in twice as many women as men. If a patient has had urticaria for up to six months then as many as 40% of these patients can suffer this condition for ten years or more.

Acute urticaria is caused by the release of certain chemical mediators within the body, the most important being histamine. Histamine is contained in the granules of mast cells. These are the large cells in the connective tissue of the skin. As histamine is released into the surrounding tissue and the blood stream, de-granulation of the mast cells occurs. Contraction of the cells lining the blood vessels, allow leakage of the intravascular fluid into the surrounding tissues causing swelling and wheal formation.

* Urticaria can occur on any part of the body.

* The condition can affect people of all ages.

* Skin lesions usually appear and disappear rapidly, lasting between a few hours to less than a day. No marks or scarring is usually apparent upon the disappearance of the wheals.

* Skin lesions can present as bright red, pink or whitish wheals in a variety of sizes, configurations and shapes. The wheals may appear as separate entities or as overlapping plaques.

There are several different types of urticaria:-
* Physical – about 4% of the population has this condition. Upon scratching the skin, linear lesions appear. The lesions are itchy but fade after about 30 minutes.

* Cold – Often found in children or young adults. The lesions are confined to the areas of skin directly exposed to the cold.

* Solar – The lesions appear after exposure to sunlight.

* Cholinergic – Sweating (usually associated with exercise, hot showers or heavy activity) causes small, prolific, extremely itchy lesions to appear.

* Contact - Usually as a consequence of intolerance to salicylates, benzoates, dyes or plants. NOTE:- in extreme cases Angioedema and Anaphylaxis can occur. These conditions require IMMEDIATE medical attention.

* Allergic – Usually associated with the intake of medicines, insect bites or foods. NOTE:- in extreme cases angioedema and anaphylaxis can occur. These conditions require IMMEDIATE medical attention.

* Delayed Pressure – this is a rare form of urticaria, taking longer to appear than other presentations. Deep swelling of the buttocks and thighs (after being seated for long periods), hands (after sport or using hand tools) and feet (after walking, running etc.) can occur. It may take up to six hours to fully develop. Although swelling is the normal presentation, in some cases, wheals may also develop.

Generalized itching is quite common during pregnancy, however, some women can develop intensely itchy papules and plaques originating in the region of the abdominal striae (stretch marks). It is more common in first pregnancies and usually resolves within weeks of giving birth. It is not associated with any foetal deaths. Recurrences during second pregnancies is not common.

The rash can spread in a symmetric pattern and can also involve the buttocks, chest, back and thighs. In severe cases the hands, feet, palms and face may also be involved.

Angioedema can be an acute or chronic recurring condition. It involves swelling similar to urticaria, but the swelling occurs beneath the skin involving the dermis and subcutaneous tissue. In urticaria, the swelling and wheals occur on the surface of the skin. Angioedema is characterized by deep swelling around the eyes, lips and sometimes the hands and feet.

Anaphylaxis is a sudden and severe allergic reaction and is often accompanied by angioedema and urticaria. The condition leads to swelling of the lips, face and throat. This causes difficult and laboured breathing which can lead to asphyxia if left untreated. Other symptoms include vomiting, diarrhoea and a drop in blood pressure.


Can be caused by a hypersensitivity to drugs or infectious diseases. Itching, burning pain, abdominal pain, fever and tiredness are all symptoms of the condition.

The condition usually presents with widespread lesions, primarily located on the lower third of the legs and ankles. In sever cases it can spread to the buttocks and arms. The lesions are bright red or purple patches or blisters and they can turn black and lead to ulceration of the affected areas.

In extreme cases, nephritis (inflammation of the kidneys) can occur. If kidney involvement is suspected, immediate medical attention is required.

In some cases there will be no diagnostic underlying cause for the generalized itch, however, in 50% of cases an underlying cause will be found and a more specific treatment then used to treat the condition.

The intensity of the itch can vary dramatically and is usually worse at night or after bathing or sweating. For the sufferer of generalized itching, their life can be totally dominated by the condition. Sleepless nights and permanent fatigue can affect work and personal relationships.

There are many factors that affect the severity of the itch including:-
* Temperature
* Humidity
* Stress and other psychological conditions such as fear or even boredom (lack of distraction)

In many cases it is the repetitive act of scratching which induces the “itching” feeling and with the continual scratching it becomes a vicious cycle.

There are many causes of pruritus, however it is usually caused by either a dermatological condition or as a secondary symptom of a systemic disease. The pruritus can either be localized or widespread.

Localized pruritus is usually caused by either a dermatosis (skin condition) or as a result of infection of a particular area:-
* Scalp – Seborrhoeic dermatitis/eczema, psoriasis
* Eyelids – Contact dermatitis
* Hands – Contact dermatitis/eczema, psoriasis, fungal infections
* Legs - Dermatitis/eczema, psoriasis
* Genitals - Dermatitis/eczema, fungal infections, psoriasis
* Feet - Dermatitis/eczema, fungal infections, psoriasis

Systemic causes of pruritus include renal disease, endocrine disorders, hepatic diseases, dehydration and psychological disorders.

Scabies (mite) infection, HIV infection, Pediculosis (lice) infection and fungal infections may also present with generalized itching.