Nettlerash, or URTICARIA (Lat. urtica, 'a nettle'), is the term applied to a common form of eruption on the skin. The eruption consists of wheals, or little solid eminences of irregular outline, and either white or red, or most commonly both red and white, there being a white centre with a red margin. The rash is accompanied with great heat, itching, and irritation, but is always aggravated by scratching; the appearance on the skin and the sensation being very much like the appearance and feeling produced by the stinging of nettles; and hence the origin of its names. The eruption is characterised by the extreme rapidity with which it appears and disappears; the whole duration of the attack may be a few hours or even less; but it is extremely apt to recur at regular or irregular intervals: it is very rare for the wheals to persist more than a day.
The disease may be either acute or chronic. In the acute form feverishness may precede the rash by a few hours, or may be altogether absent. The disorder is often connected with some derangement of the digestive organs, and may be traced to the imperfect digestion of special articles of food, such as oatmeal, the kernels of fruit, strawberries, cucumbers, mushrooms, and especially oysters, mussels, and crabs, which are eaten with perfect impunity by most persons. It may be brought on also by local causes of irritation, and frequently complicates other irritable diseases of the skin.
The chronic form is often very troublesome, and frequently comes on periodically in the evening. Cases are reported in which persons have been afflicted for ten years continuously by this form of the disease. It is characterised by constant recurrence during long periods, not by persistence of a single outbreak of the eruption. In the treatment of the acute form local causes of irritation must first be looked for and removed. Where it is brought on by some article of diet relief is often obtained by taking a teaspoonful of bicarbonate of soda (baking soda); but it may be necessary to administer emetics and purgatives, if vomiting and diarrhoea do not occur spontaneously. In the chronic form the patient should, in the first place, determine whether the rash is caused by any particular article of diet, and if this seems not to be the case an attempt must be made to improve the state of the digestive organs. A few grains of rhubarb taken daily, just before breakfast and before dinner, will sometimes effect a cure. Numerous other remedies have been recommended; perhaps the most generally useful is a draught containing a scruple each of the carbonates of magnesia and soda with five drops of tincture of nux vomica. Although external applications are usually of little avail, dusting the itching surface with flour sometimes affords temporary relief; and a still more useful application is a lotion composed of a drachm of the carbonate of ammonia, a drachm of the acetate of lead, half an ounce of laudanum, and eight ounces of rose-water.