More than half the people in the United States are sensitive to poison ivy, poison oak, and poison sumac and develop an itchy, blistering rash after coming in contact with these plants.

• Poison ivy is generally found east of the Rocky Mountains, grows as either a vine or a shrub, and has leaves that have a smooth surface, slightly notched edges, and often clusters in groups of three.

• Poison oak is a small bush, sometimes a climbing vine, with smooth-edged leaves clustered in groups of three, five, or seven and more commonly found west of the Rockies.

• Poison-sumac leaves are generally smooth and oval shaped with seven to thirteen on each stem and grow in wet areas of the Southeast. The appearance of each of these plants can vary depending on region and seasons.

Symptoms of Poison Ivy, Oak, and Sumac Rash

Exposure to any of these plants in sensitive people causes an itching rash usually appearing within 24 to 72 hours. The rash begins with small red bumps, developing into blisters of variable size later.

The rash also may crust or ooze and is often in streaks (straight lines), but can take any shape or pattern, and different areas of the body can develop a rash at different times, which may make it seem like the rash is spreading.

First Aid for Poison Ivy, Oak, and Sumac Rash

Blisters may break open, but the fluid from blisters does not spread the rash; it's only spread by actual exposure to the oil that may linger on hands, clothing and shoes, or tools that act as carriers.

Take special care while burning campfires in areas with poison ivy, as inhaling the smoke of a burning poison-ivy plant can be life threatening. When you are exposed to any of these plants or their oils:

• Wash with soap and water thoroughly as soon as possible.

• Apply cold compresses with water or milk, calamine lotion, or Aveeno oatmeal bath; and take oral antihistamines such as Benadryl (diphenhydramine hydrochloride) and 1% hydrocortisone to help alleviate symptoms.

• For feelings of lightheadedness, lie down and raise your legs higher than your head to help blood flow to your brain.

• If you begin to wheeze or have difficulty breathing, use an inhaled bronchodilator such as albuterol or epinephrine if it is available in order to dilate the airway, or if you have prescribed epinephrine, use it as you have been instructed.

Your doctor may also prescribe oral steroids to treat your poison ivy.