
Originally Posted by
cj1capp
Urticaria (Hives or "Nettle" Rashes)
by Dr Adrian Morris
Urticaria is a raised itchy and painful skin rash sometimes called a “nettle rash” or hives. There are two distinct types of urticaria:
· Acute urticaria is often caused by an allergy to food or medication and can last between several hours and six weeks.
· Chronic urticaria is diagnosed if the rash persists for six weeks or longer, the underlying cause is then usually not due to food allergies.
What are the causes?
Acute Urticaria
The most likely cause of Acute Urticaria is an allergy due to exposure to pets, horses, latex rubber, food such as shellfish, nuts, egg and dairy products or bee and wasp stings. Allergies to medication such as antibiotics (penicillin, tetracycline, sulphonamides and cephalosporins), blood pressure pills (ACE inhibitors and diuretics), codeine and aspirin containing pain killers can cause acute urticaria. Sometimes viral infections such as glandular fever and hepatitis B, or bacteria (helicobacter, streptococci), fungal and parasitic infections can trigger urticaria. Allergic reactions to blood products, transfusions, xray contrast and vaccines have also been implicated. Papular urticaria is the medical term for “itchy bumps” or grouped urticarial lesions seen mainly in children and which follow insect bites from midges, fleas and mosquitoes.
Chronic Urticaria
The cause of Chronic Urticaria is much more difficult to identify. The role of true food allergy is hardly ever a significant trigger but food additives such as salicylate, sodium benzoate, colourings and nitrites may play a role. We often end up diagnosing Chronic Idiopathic Urticaria. This condition (which can persist for many years) is due to the production of “auto-antibodies” which in turn attack specific Mast Cells in our skin and tissues causing an enormous release of histamine. Why we suddenly switch-on production of these aggressive antibodies to our own skin cells is a complete enigma. Our bodies may continue producing these auto-antibodies for a number of years leading to a great deal of distress and discomfort for the urticaria sufferer. Unfortunately over 50% of Chronic Urticaria cases are due to production of these “auto-antibodies” to the IgE and its receptor on Mast Cells found in the skin.
Chronic parasitic infections and ACE inhibitor blood pressure pills may play a role in both acute and chronic urticaria. Stress is known to aggravate urticaria and stress reduction measures are very important in treating chronic urticaria.
Chronic urticaria can also be triggered by physical factors such as exposure to environmental heat (prickly heat), intense cold, sunlight, vibration or pressure on the skin (from tight clothing). Very rarely some people react to bath water, this is called “Aquagenic” Urticaria. Exercising after eating certain foods such as wheat, celery and shellfish might provoke delayed urticaria. Many people have very sensitive skin and any friction or rubbing will cause raised red lines to develop. This is called Dermatographism and indicates just how easily they can release histamine in their own skin. A good test for cold urticaria is to hold a block of ice against the skin for 5 minutes and see if an urticaria weal develops after the ice is removed.
Underlying thyroid diseases and autoimmune diseases such as Systemic Lupus and Rheumatoid Arthritis can provoke Chronic Urticaria or even Urticarial Vasculitis (a variant in which the lesions tend not to fluctuate but lead to skin discolouration). Urticarial Vasculitis may be associated with a fever, bone pains and joint swelling (Schnitzler’s Syndrome).
Occasionally an inherited deficiency of the C1 Esterase Inhibitor Enzyme leads to a non-itchy form of urticaria called Hereditary or Familial Angioedema. This condition affects mainly females in a family, is associated with sudden swelling of the face and neck which is not itchy but tends to be painful. These lesions usually last for 2 to 3 days and do not respond to antihistamine medication. Sufferers characteristically have low levels of the Complement C4 in their bloodstream and respond to medication called Danazol or Tranexamic acid which prevents attacks.