|
Urticaria or hives is a local or generalised blotchy rash which often occurs with skin irritation. Sometimes it can coincide with angio-oedema. These allergic developments are the result of a fast influx of fluid under the skin causing an acute swelling. Sometimes the symptoms are severe and may lead to shock, see section entitled Anaphylaxis. Skin irritation can occur alone without any visible skin changes.
Some unusual types of urticaria or hives include: (a) solar apparently caused by the sun (b) cold i.e. caused by exposure to cold air or ice (c) water-induced e.g. while having a shower (d) dermographia i.e. the condition whereby lines or letters can be drawn on someone’s skin (e) auto-immune or idiopathic, suggesting the absence of an obvious cause and (f) some blood disorders including Hodgkin’s lymphoma and leukaemia and advanced cancer.
In our experience, types (a)-(e) above often obscure some other underlying factors which cause the immune system to be in a continuous state of alertness. For example solar urticaria in some cases is the result of using a suntan lotion during sun-bathing which becomes an irritant in the presence of sun and local heat. Immediate reactions to some foods e.g. peanuts or seafood are also uncommon causes.
Some common causes of urticaria:
-
Type B food, delayed allergy or intolerance
-
Intolerance to common colourings, preservatives and other additives, often seen in children, which promote histamine release
-
Reactions to common medications such as penicillin or aspirin
-
Reaction to chemicals naturally found in some foods
-
Sensitivity to some fungi
-
Allergy to common inhalants i.e. pollens, cat or dog dander, horse hair
Most of the above factors tend to mimic symptoms of immediate or severe allergy but often involve different mechanisms from those causing an immediate allergy without its risks. Contrary to popular belief, intestinal parasites do not cause urticaria.
Investigations
If immediate or severe allergy is suspected, it is safer to test immunoglobulin-E’s in blood samples. Skin prick tests are best avoided as they carry a risk of potentially severe reactions.
Whilst skin prick tests are widely accepted by the medical profession as accurate and reliable, they are flawed by the fact that they frequently miss delayed allergies e.g. food intolerance.
Instead we recommend a number of practical dietary changes and specific blood or intradermal tests. Foods and many other substances can be tested this way.
|
