Urushiol is spread by contact but can be washed off with a strong grease- or oil-dissolving detergent and cool water and rubbing ointments. Dermatographic urticaria
Dermatographic urticaria (also known as dermatographism or "skin writing") is marked by the appearance of weals or welts on the skin as a result of scratching or firm stroking of the skin. Seen in 4–5% of the population, it is one of the most common types of urticaria, in which the skin becomes raised and inflamed when stroked, scratched, rubbed, and sometimes even slapped.The skin reaction usually becomes evident soon after the scratching and disappears within 30 minutes. Dermatographism is the most common form of a subset of chronic hives, acknowledged as "physical hives".It stands in contrast to the linear reddening that does not itch seen in healthy people who are scratched. In most cases, the cause is unknown, although it may be preceded by a viral infection, antibiotic therapy, or emotional upset. Dermatographism is diagnosed by applying pressure by stroking or scratching the skin. The hives should develop within a few minutes. Unless the skin is highly sensitive and reacts continually, treatment is not needed. Taking antihistamines can reduce the response in cases that are annoying to the person. Pressure or delayed pressure
This type of hives can occur right away, precisely after a pressure stimulus or as a deferred response to sustained pressure being enforced to the skin. In the deferred form, the hives only appear after about six hours from the initial application of pressure to the skin.
The appearance of hives is within one to 15 minutes of contact with the water and can last from 10 minutes to two hours. This kind of hives does not seem to be stimulated by histamine discharge like the other physical hives. Most researchers believe this condition is actually skin sensitivity to additives in the water, such as chlorine. Water urticaria is diagnosed by dabbing tap water and distilled water to the skin and observing the gradual response. Aquagenic urticaria is treated with capsaicin (Zostrix) administered to the chafed skin. This is the same treatment used for shingles. Antihistamines are of questionable benefit in this instance since histamine is not the causative factor. Exercise
The condition was first distinguished in 1980. People with exercise urticaria (EU) experience hives, itchiness, shortness of breath and low blood pressure five to 30 minutes after beginning exercise. These symptoms can progress to shock and even sudden death. Jogging is the most common exercise to cause EU, but it is not induced by a hot shower, fever, or with fretfulness. This differentiates EU from cholinergic urticaria.EU sometimes occurs only when someone exercises within 30 minutes of eating particular foods, such as wheat or shellfish. For these individuals, exercising alone or eating the injuring food without exercising produces no symptoms. EU can be diagnosed by having the person exercise and then observing the symptoms. This method must be used with caution and only with the appropriate resuscitative measures at hand. EU can be differentiated from cholinergic urticaria by the hot water immersion test.