This section is from the book "Hartmann's Theory Acute Diseases And Their Homoeopathic Treatment", by Charles J. Hempel. Also available from Amazon: Theory of acute diseases, and their homoeopathic treatment.
§ 102. Nettle-rash, Urticaria.
This disease is sometimes preceded by catarrhal symptoms for two or three days. Spots or blotches form on the skin, of a palish-red or white colour, irregular shape, with bright-red circumference. They itch violently, and excite even a violent burning. Frequently the blotches are elevated, rough to the feel, numb and insensible, and resemble bee-stings. When deep-seated in the skin, they are brought to light by friction and scratching. Sometimes they appear distinctly in a few hours. They are exceedingly evanescent, and frequently appear and disappear on the same day. Both in shape and sensation they resemble the blotches occasioned by nettles, and are distinguished by the peculiarity of disappearing in warm and coming out in cold weather. They are liable to constant changes of locality, to such a degree that a blotch frequently does not remain at one spot for an hour. Their retrocession is seldom accompanied with an alteration of health, but is sometimes accompanied with slight fainting spells, headache and other symptoms, especially when the first appearance of the rash was attended with fever. The disease is apt to be excited by sudden changes of temperature, colds, indigestion, excessive eating and drinking; in some individuals the rash appears after the use of strawberries, crabs and muscles.
If the rash should have been occasioned by a cold, or if it should be itching and if scratching should induce a burning sensation, or if the eruption should be preceded by a stinging sensation all over the body, Dulcamara is the best remedy. Next to Dulc, Rhus t. is the most suitable remedy, especially when the rash is accompanied by a little fever. Nux and Pulsatilla, and still more frequently Antimonium crudum, Bryonia, Arsenic,* are indicated when the rash originates in indigestion. Hepar s., and Mercurius, are likewise useful in some cases. Copaiva is an admirable remedy for some kinds of urticaria, particularly chronic, or when arising from a syphilitic or arthritic cause. Ignatia should be administered for a fine-stinging, burning itching without rash, which sets in in the evening, and disappears after scratching. Kali carb. is one of the best remedies for nettle-rash when occurring in females at the period of menstruation, and exciting a troublesome itching over the whole body. A disposition to a frequent recurrence of nettle-rash is to be met by one of the following remedies: Carb. veg., Calc. carb., Sulphur, Magnesia sulph., Nitric ac, Causticum, Lycopodium, Conium, Veratrum, Petroleum, Natrum mur., Phosphorus.