The Hiker's Guide to Poisonous Plants

Before they take to the trails, hikers should understand the dangerous plants they might face on their journey. Contact with poisonous plants can result in everything from an irksome rash to more severe central nervous system complications. In extreme cases, poisonous plants can cause death. Although wearing protective clothing can reduce the risk of contact with poisonous plants, being able to identify these plants keeps hikers safe on the trails. Understand the characteristics, symptoms, and treatment for common poisonous plants.

Poison Ivy

Hikers can easily identify poison ivy by looking for three glossy, oval leaflets, two lateral and one in the center. Leaf color changes with the season; poison ivy leaves are green in the summer but change to shades of yellow, orange, and red in the fall and spring. The hairless poison ivy leaves range from three-fourths of an inch to four inches long. Poison ivy grows on woody stems, often climbing on nearby vegetation.

Hikers might mistakenly think that simply touching a poison ivy leaf causes a rash. The leaf is not poisonous; instead, its sap causes the rash. This poisonous sap covers a broken or bruised poison ivy leaf or one that has been damaged. Hikers exposed to the sap will experience swollen, red, itchy skin along with broken and oozing blisters, all of which can appear anywhere from six hours to two weeks after exposure.

Hikers exposed to poison ivy should wash the area with soap and water within 10 to 20 minutes, if possible, to reduce the risk of a rash. If they do contract a rash and blisters, they should avoid scratching the blisters, which can cause infection. Over-the-counter skin medications, such as calamine lotion, and cool baths can ease the itchiness. Antibiotic ointment prevents broken blisters from becoming infected.

  • Weed Identification Guide - Virginia Tech’s Weed Identification Guide describes the distinctive characteristics of poison ivy and includes pictures of the plant.
  • Poison Ivy Health Information - This resource explains the symptoms, prevention, and treatment of poison ivy.
  • Outsmarting Poison Ivy - The Food and Drug Administration (FDA) offers tips on recognizing, avoiding, and treating poison ivy.

Poison Sumac

Poison sumac is in the same family as poison ivy but is larger, the size of a small tree or large shrub ranging from five feet to 20 feet. The plant consists of nine to 13 untoothed leaflets connected by a red rachis, or stem. Poison sumac in the spring or summer features green leaves accompanied by green flowers and white fruit. In the fall, the plant changes to vibrant hues including yellow, scarlet, and purple.

Poison sumac sap envelopes all of the plant, so simply brushing up against the leaves can result in a reaction for hikers. Hikers who have contact with poison sumac will experience swelling, itching, and redness, similar to poison ivy. They should wash their hands and under their fingernails immediately to prevent spreading the rash. Both antihistimines and oral and topical steroids can reduce the swelling and itching that comes with poison-sumac contact.

  • Poison Sumac - This page offers many pictures and a brief description of poison sumac plants.
  • Florida Forest Plants - This resource analyzes the identifying characteristics of poison sumac.
  • Poison Ivy and Poison Sumac – This article describes poison sumac and offers pictures of the plant and the rash it can cause.
  • Poison Control Center - This article discusses the treatment and prevention of poison sumac.

Poison Oak

Like poison ivy, poison oak features three-parted, shiny leaves that are green, red, orange, yellow, or reddish black, depending on the season. Poison oak leaves grow on light brown or gray stems, ranging from one foot to six feet tall. In the spring, poison oak leaves include yellow-green flowers that turn to white berries in the summer. The plant can be difficult to identify, as it grows as a shrub, vine, or ground cover.

Contact with the oil on poison oak leaves results in burning, itching skin followed by a rash. Thoroughly washing the hands and the affected area can prevent the rash from spreading. Hikers who come into contact with poison oak can relieve their symptoms by taking an oatmeal bath. Applying hydrocortisone cream or taking an antihistamine can treat poison-oak symptoms as well.

  • Poison Oak - This article discusses the identification, prevention, and treatment of poison oak.
  • Poison Oak Relief - This resource explains how to relieve poison-oak symptoms.
  • Poison Oak in the Forest - This article helps hikers identify and avoid poison oak.


Best known as a Christmas decoration, holly bushes include green leaves featuring pointed tips and red berries. The leathery holly leaves are typically two to four inches long. Holly, which can grow from 15 to 30 feet tall, has a grayish-brown bark and horizontal branches. The berries mature in the early fall but often stay on the bush through the winter and into the spring.

Although the holly leaves are not poisonous, the berries can be dangerous if hikers ingest them in large quantities. Eating the berries can result in nausea, vomiting, and diarrhea. In more extreme cases, ingestion of holly berries can cause central nervous system depression. If hikers ingest holly berries and experience these symptoms, they should go to an emergency room for treatment immediately.

  • Poison Holly – This essay offers information about the poisonous holly plant.
  • Common Plants - This comprehensive document lists the symptoms of poisonous holly exposure.
  • American Holly - This fact sheet describes the characteristics of the American holly.

Wood Nettle/Stinging Nettles

Stinging, or wood nettle plants feature triangular or heart-shaped leaves that decrease in size as they go up the slender stem. The leaves are one to six centimeters long and one to four centimeters wide with linear bumps, and the plant typically is three feet to six-and-a-half feet tall. Singing nettles also include green flower clusters and brown seed-like fruit. Most notably, the plant has stinging hairs.

When these stinging hairs come into contact with skin, they break the skin and release an irritant that causes redness and severe itching. These symptoms are typically brief but can be quite uncomfortable. Hikers who come into contact with stinging nettles should wash the affected area with soap and water. Creating a paste of water and baking soda can also alleviate the itching and irritation.


Commonly known as poison parsley or spotted parsley, poison hemlock’s most prominent feature is its purple-blotched stem. The dangerous plant grows up to ten feet tall and has leaves and flowers similar to parsnips or carrots. Its foliage resembles fern leaves. Fresh hemlock emits a musty odor, another distinctive characteristic of the plant.

Hemlock is highly poisonous and can cause death if ingested. The plant is perhaps best known for killing philosopher Socrates, who ingested its juice to commit suicide. If hikers mistakenly ingest hemlock, they will experience nausea, vomiting, confusion, a burning mouth, muscle paralysis, and respiratory distress. They should immediately go to an emergency room for treatment, as hemlock ingestion can be deadly.