Poisoning is usually caused by contact with some part of the plant. A very small quantity of the poisonous substance is capable of producing severe inflammation of the skin and can easily be transferred from one object to another. Clothing may become contaminated and is often a source of such prolonged infection that it is likely to be judged as a case of poisoning difficult to cure. Dogs and cats frequently touch the plants and transmit the poison to unsuspecting persons. The poison may remain on the fur of animals for a considerable period after they have walked or run through poison-ivy plants. Smoke from burning plants will carry the toxin and has been reported to cause severe cases of poisoning. Cases of poisoning of children from eating the fruit have been reported. A local belief that eating a few leaves of these plants will develop immunity in the individual is unfounded. It never should be attempted. No part of the plant should ever be taken internally, as it is a violent irritant and poisonous to man.
Cattle, horses, sheep, hogs, and other livestock apparently do not suffer from skin irritation caused by these plants, although they have been observed to graze upon the foliage occasionally. Bees collect honey from the flowers, though no reports are on record of any ill effects from the use of the honey.
The time between contamination of the skin and the first symptoms varies greatly with individuals and probably with conditions. The first symptoms of itching or burning sensation may develop in a few hours or after 5 days or even more. The delay in development of symptoms is often confusing in attempting to determine the time or location when contamination occurred. The itching sensation and subsequent inflammation, which usually develops into water blisters under the skin, may continue for several days from a single contamination. Persistence of symptoms over a long period is likely to be due to new contacts with plants or with previously contaminated clothing or animals. Severe infection may produce more serious symptoms, which result in much pain through abscesses, enlarged glands, fever, or complicated constitutional malfunction. Secondary infections are always a possibility in any break in the skin, such as is produced by breaking vesicles that have formed as large water blisters.
PRECAUTIONS AGAINST POISONING
The most effective way to prevent poisoning from the plants is to avoid contact with them. If it is necessary to work among them, some measure of prevention can be gained by wearing protective clothing, but it is necessary to remember that the active poisonous principle can easily be transferred. Some protection also may be obtained in advance by the use of protective creams or lotions. They prevent the poison from touching the skin, or make the active principle easily removed, or neutralize it to a certain degree.
Various formulas containing ferric chloride and glycerin have been used more or less effectively as a preventive measure, although there may be some danger of pigmentation of the skin from the ferric chloride. A common formula is ferric chloride, 5 parts; glycerin, 25 parts; alcohol, 25 parts; water. 50 parts.
A lotion of this formula applied to the exposed skin prior to contact with poisonous plants gives effective protection for many people. It is especially effective if followed by thorough washing with soap and water. Such washing, even if no protective lotion has been used, is often effective in preventing poisoning. Proper precaution should be taken by repeated lathering with a strong alkali soap, followed by thorough rinsing and repeating the process several times. The water should be frequently changed, and a shower or flowing water bath is preferable. The soap probably only emulsifies the active principle, and thorough rinsing is necessary to avoid spreading the poison to other parts of the body.
The United States Public Health Service reports successful chemical protection against ivy poisoning by use of an oxidizing agent—sodium perborate prepared and used fresh as an ointment. Following is a formula given for the ointment: Cetyl alcohol, 35.1 percent; stearyl alcohol, 5.3; ceresin, 3.5; castor oil. 20.8; mineral oil, 21.9; Duponol WA pure, 1.7; sodium perborate. 10.0; and boric acid, 1.7 percent.