Poisonous plants

Anatomy or system affected: Gastrointestinal system, immune system, skin, stomach

Definition: Plants that cause gastrointestinal or dermatological reactions in humans

Some plants manufacture substances to assist themselves in survival. These chemicals can cause irritation or allergic reactions in organisms that contact them. Among human beings, the most common reaction is an allergy. The specifics of an allergic reaction can vary widely and range from no apparent reaction to shock. Allergic reactions to contact with most plants are uncommon and classified on an individual basis. Some plants, however, cause reactions in virtually everyone with whom they come into contact. As a result, they are termed poisonous plants. Many commonly encountered poisonous plants cause reactions in the skin, while some plants can cause adverse systemic reactions when ingested. The reaction of skin to plant toxins is termed dermatitis. These reactions are rarely fatal but have widespread morbidity.

Poison oak, poison ivy, and poison sumac. Poison ivy (Toxicodendron radicans) is widely distributed throughout the United States. This is a vine with groups of three shiny green leaves. Poison oak (Toxicodendron diversilobum) is a low shrub with leaves that also come in groups of three to a stem; it is found in dry areas. Poison sumac (Toxicodendron vernix) is a taller plant with slender leaves arranged in pairs along a stem and a single leaf at the end of the stem. It grows in damp or swampy areas.

Contact with any of these plants leads to a reaction in the skin at the site of contact. An individual’s first contact with these plants causes no apparent reaction; sensitization must occur. In the days (usually between five and twenty) following the initial exposure, the immune system causes the entire body to become sensitive to the plant’s chemical irritant. If the plant is touched on another occasion, a reaction will occur. The second reaction commonly causes itching (pruritus), redness (erythema), and swelling (edema) at the site of contact. Vesicles filled with a clear fluid may develop. Proper treatment consists of washing the area of contact as soon as possible, then keeping the area dry until the vesicles become crusty and disappear. This process normally requires up to ten days. Physicians sometimes use corticosteroids to manage serious cases of contact dermatitis.

Scratching to relieve urticaria may break the surface of the skin and introduce infection to the affected area. This may prolong the healing time and lead to scarring. The clear, watery fluid found in vesicles does not contain plant material and cannot spread the rash to other parts of one’s own body or to other individuals, but a thicker, cloudy material (pus) may be found in vesicles that have become infected by scratching. Pus can transmit the infection, but not the rash, to other individuals.

Sensitivity to poison ivy and poison oak is usually lifelong. Sensitivity to other plants is more individual in nature and is dependent on factors such as the magnitude of the initial exposure, the number of subsequent exposures, and an individual’s body chemistry and immune status.

Mushrooms. Although mushrooms appear harmless, they can cause a variety of reactions when ingested. There are five broad types of reactions: gastrointestinal discomfort with nausea, vomiting, and diarrhea; sweating; inebriation or hallucination without sleep; delirium with sleep or coma; and vomiting only when associated with alcohol. Some mushrooms produce reactions only after delays of six hours to three days. These reactions include headaches, extreme thirst, nausea, and vomiting.

The gastrointestinal symptoms associated with mushroom intoxication usually appear within three hours of ingestion. The resulting discomfort is transient. Sweating is caused by the presence of a chemical that is not inactivated by cooking. The symptoms usually subside within two hours.

Psilocybin, a chemical that causes hallucinations, is found in some mushroom species. The effect usually lasts approximately two hours, although the extent of a reaction is determined by the amount ingested, the setting, and the mood and personality of the individual.

Delirium associated with sleep or coma is encountered with ingestion of Amanita muscaria and Amanita pantheria species. Within approximately thirty minutes of ingestion, an individual becomes drowsy. This may be followed by elation and extreme activity, again followed by a period of drowsiness. This alternating cycle may continue for up to twelve hours. Coprinus atramentarius is an edible mushroom that sensitizes the body to alcohol. For approximately three days after ingestion, a chemical contained in the mushroom reacts with alcohol to cause vomiting.

All mushroom species contain some amount of mycotoxins that may or may not be affected by cooking. The best guideline is to avoid eating any mushroom unless it is either purchased in a store or positively identified by an expert.

Other common poisonous plants. Contact with plants called nettles (Urtica urens and Urtica dioica) can cause intense reactions. The plant is common in well-watered areas throughout North America.

Contact with plants of the carrot (Umbelliferae) family such as caraway, dill, parsley, and parsnip can cause a brief sensitivity of the skin to ultraviolet light. Exposure to sunlight or fluorescent light within six to twenty-four hours after contact with the plant may lead to burning of the skin exposed to the chemical—a sunburn. Citrus plants of the rue (Rutaceae) family can also cause this skin photosensitivity. It can be prevented by thoroughly washing the skin after contact. Inflammation after exposure can be treated with aspirin.

Inquiries concerning the ingestion of plant materials account for about 10 percent of all calls to poison control centers. The single plant species that is involved in the greatest number of adverse reactions is Dieffenbachia. Other house plants, such as philodendron, poinsettia, holly, honeysuckle, jade plant, and yew, may accidentally be ingested by children. Individual reactions to ingested house plants vary; specifics are dependent on the species and amount ingested, the specific plant part ingested, the body size of the individual, and how quickly the plant material is removed from the body. Once in the body, most plants cause vomiting and diarrhea. Other reactions vary and are specific to the plant species involved. Dieffenbachia causes immediate burning pain and swelling in the mouth.

Leaves of several plants in the Solanum family, such as nightshade, jessamine (jasmine), and the immature fruit of some ground cherries and European bittersweet, contain a chemical that can cause intense gastroenteritis. These plants are especially toxic to small children. If ingested, jimsonweed may cause delirium. Common flowers such as lily of the valley, foxglove, and oleander contain chemical substances that can cause the heart to malfunction.

Bibliography

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