In both nettle rash and angioneurotic oedema, the cause for the condition is a disturbances in the immune system. In nettle rash, the alterations only take place in the skin itself where the itching swellings occur. The appearance of it is red with a white centre resembling what happens when you actually get stung by a nettle.
In angioneurotic oedema, liquid will seep out from the blood vessels in a particular area of the body and that area will be swollen. Besides the visible places, the seepage can also take place in the gastro-intestinal canal. What happens is that certain large cells of the immune system, mast cells, liberate the substance histamine which then triggers the swellings.
There are many different things that can provoke such an attack: Cold, light, exercise, vibrations, and pressure against the skin. It might also be a case of hypersensitivity towards pollen, towards particular food items such as shellfish and fruits, and/or towards fungi or mildew (e.g. on window frames).
The tendency can be hereditary because of the lack of a certain inhibitory enzyme or the enzyme can be absent because of a lymphatic suffering. Certain kinds of medication, e.g. antibiotics, certain X-ray contrast media, acetylsalicylic acid, rheumatic medicine of the ibuprofen type (NSAIDs), and certain colouring agents and preservatives (benzoates) can also trigger these swellings.
It is, of course, important to try to find the cause of the disease and then as far as possible avoid it; but this is not always possible.
