There are many reasons to love plants, not the least of which is their beauty and usefulness. Many plants are not only visually attractive, but they are also good to eat, have a pleasing scent or can be used for medicinal purposes. Some plants, however, should not be touched without protection. Contact with the sap or leaves and stems of these poisonous plants can cause dermatitis of the skin. Contact dermatitis usually causes a localized rash, blisters, hives or swelling, along with pain or itching of the skin.
Chrysanthemums (sometimes called mums) are a highly desirable, late-summer flowering plant. These hardy, beautiful flowers, which come in autumn colors, are often planted in containers for late summer or early fall color. Many home gardeners do not realize that unprotected contact with the leaves or flowers of mums can cause dermatitis. The affected skin will become red with a brief contact. Prolonged exposure to these parts of the plant will cause blisters and even scales to develop. The longer the contact, the more severe the reaction will be. For these reasons, chrysanthemums should be planted or displayed out of reach of children.
Poison sumac, unlike mums, is not cultivated by home gardeners. Contact with the plant usually occurs by accident during outings in forests. Poison sumac grows in the underbrush of forested areas. The plant is distinctive due to its long stems lined with green and purple leaves. Contact with poison sumac causes itchy skin, which later swells up and turns bright red. Prolonged contact causes blisters to form.
Poison ivy is one of the most well-known poisonous plants. Unprotected contact with this vine, which can grow along the ground or up and over plants, causes itchy skin at first. Red spots usually develop, which can turn into blisters in serious cases. Like all contact dermatitis reactions to poisonous plants, if you wash the affected skin immediately with warm, soapy water, you can reduce the eventual seriousness of the reaction.
Giant hogweed is a large, impressive plant, but sap from any part of the plant can cause severe blistering of the skin. In most cases, the blistering does not happen right away, because the sap must be activated by exposure to the sun. This is called phototoxicism. Usually, the skin will turn red a day after contact and develop serious blisters two days after the initial contact. The blisters can leave scars.