The rash can appear on different parts of the body at various times. This may happen because the parts were exposed at different times, or because areas with thicker skin are less easily penetrated by the oil. The delicate skin of the genital and perianal areas, for example, is more easily breached than tougher skin on the hands.
我古狗查了poison ivy的信息。Poison ivy中文叫毒藤,你徒手去拔时,会接触到the plant’s oily sap, urushiol(漆酚). Poison ivy的stems, roots, flowers and berries all contain urushiol.下面是我在网上看到的一篇讲poison ivy的文章,直接copy过来。
“ (ZT) …Touching or brushing against any of these plant parts, even if they are dead, can cause a reaction. The sap is hardy and can cause a rash in the dead of winter, or even a year after contaminating clothing or shoes that are not thoroughly cleaned.
Urushiol shows up elsewhere, including in the skin of mangoes (and the leaves and bark of the mango tree), as I discovered when I ate a mango still in the rind and ended up with a blistering rash on my mouth. Cashew shells also have the toxin, which is why cashews are sold shelled and processed (either roasted or in the case of “raw” cashews, steamed) at a temperature high enough to destroy urushiol. Poison ivy is not the only problem plant one might encounter while hiking, camping or simply strolling in the countryside. T. radicans has two relatives, poison oak and poison sumac, that don’t always form the classic clusters but are equally toxic troublemakers.
First, learn to recognize the plants in their various growth patterns. While poison ivy is most often encountered as a small ground plant, it also grows as a shrub and vine. The vines, which turn bright red in fall, were once used to adorn buildings in England.
Poison oak, which has compound leaves made up of three (or sometimes five) leaflets, usually grows as a shrub, but will form a vine in the Western states.
Poison sumac, which grows as a tall shrub or small tree, produces leaves with rows of paired leaflets and a single leaflet at the end. It likes a wet habitat, growing in peat bogs in the Northeast and Midwest and swamps in the Southeast.
Urushiol can penetrate cloth. Although long sleeves, pants and gloves can reduce the risk of exposure, they cannot guarantee protection. Even rubber gloves can be breached. If you must handle the plants or are likely to contact poison ivy when gardening, wear vinyl gloves.
You don’t have to touch the plant directly to react to urushiol. Gardening tools, sporting equipment, even a pet that has been in a patch of poison ivy — all can cause a reaction.
Before possible exposure, use an over-the-counter skin-care product containing bentoquatam (IvyBlock) to prevent or reduce absorption of urushiol. The combination of this barrier product and protective clothing is your best defense against an inadvertent encounter.
Contrary to popular belief, a poison ivy rash is not contagious. It cannot be spread by oozing blisters, or by scratching or touching the rash. Only direct contact with urushiol causes a reaction. (Scratching can result in an infection, however.)
Never try to burn a poison plant. Burning releases the toxin, which may land on skin or, worse, be inhaled and cause a serious internal reaction.
Should you contact a urushiol-containing plant, the American Academy of Dermatology recommends washing your skin immediately. Lukewarm, soapy water is best, but even plain water can limit exposure to the sap. Take care in removing contaminated clothing, and wash it separately as soon as possible.
You can relieve a rash by applying cool compresses with an astringent like Burow’s solution, soaking the affected area in colloidal oatmeal, or using calamine lotion; all are sold over the counter. Do not apply products containing a topical antihistamine, like Benadryl, which can cause a sensitivity reaction that makes matters worse.
Severe reactions may require medically prescribed treatment with an oral corticosteroid like prednisone.”
It's not poison ivy. Poison ivy has trifoliate leaves. This is magenta spreen, edible. http://www.johnnyseeds.com/search.aspx?searchterm=magenta+spreen&isusersearch=1.