The allergic process can affect the skin producing 2 main types of rashes namely urticaria (hives, nettle rash, welts) or eczema (see atopic dermatitis).
Urticaria is a red itchy bumpy rash that is often short-lived and can appear in various shapes and sizes anywhere on the body. It is very common affecting 1 in 5 of the population at some time in their lives. In some people urticaria is accompanied by large dramatic swellings commonly affecting lips, eyelids, tongue and hand called angioedema.
In many individuals, no cause can be found for the urticaria and angioedema but it can occur as part of an allergic reaction such as to foods, drugs, insect stings. Sometimes external/physical stimuli can provoke the condition such as sunshine, water, pressure on the skin, exercise and stress.
Angioedema without urticaria can occur and may be related to blood pressure-lowering drugs called ACE inhibitors and examples of this group are lisinopril, enalapril and ramipril.
Interestingly these reactions often start after several months/years of regular treatment and hence this important association must not be overlooked. Release of histamine in the skin produces urticaria and therefore antihistamines are the mainstay of treatment.
The non-sedating ones are most suitable such as cetirizine, fexofenadine and loratadine. In some individuals, the rash persists over weeks and months and this chronic form may require specialist intervention to allow the condition to be appropriately treated.