Plant-induced allergic or irritant skin rashes are very common. There are numerous plants that will cause an irritant reaction in many people and an allergic reaction in sensitive people. In fact, poison ivy, poison oak and poison sumac are the most common causes of allergic reactions in the United States, according to the American Academy of Dermatology.

Skin rashes caused by plants can develop hours or days after contact with the plant, depending on the sensitivity of the person. Redness will develop at the contact site, followed by blisters, and sometimes swelling. A rash can occur anywhere on the body, but may be especially likely on thin skin, such as the face. Plant rashes normally take about 10 days to heal on their own.

The best way to avoid a plant-related skin rash is to avoid the plants that cause reactions. This will require knowledge of the poisonous plants that naturally grow in the region, and the house and garden plants in the area that may cause an allergic or irritant skin reaction.

Skin rashes are often first recognized by the person experiencing symptoms. However, it may be necessary to consult a physician for severe reactions or lasting rashes. If a reaction is allergic in nature, physicians may perform allergy tests to identify the specific allergen (substances that trigger an exaggerated immune system response) causing symptoms. Anyone experiencing a severe allergic reaction (anaphylactic shock) characterized by swelling and difficulty breathing should seek immediate medical treatment.

Skin exposed to a questionable plant ideally should be washed with water immediately after contact. Washing with soap and water within 30 minutes of contact may still help prevent a rash from developing or spreading. Soap and water can also be used on clothing, shoes, pets or tools that came into contact with the plant. Lotions, such as calamine lotion, and cool oatmeal baths can be used to soothe the irritated skin.

Physicians may recommend one or more medications to help relieve symptoms. Corticosteroid creams may be recommended to reduce swelling, redness and itching. In severe cases, corticosteroids may have to be given internally. Antihistamines may be necessary for allergic reactions. If an infection develops in the rash, antibiotics may be necessary to treat the infection.

The primary method of preventing plant rashes is to avoid the plant that triggers reactions. However, it is not always possible for people to know when they are likely to come into contact with problems plants. Protective clothing (e.g. gloves, long sleeve shirts) is essential. Barrier creams that prevent skin exposure to irritants or allergens may also be helpful for some people.

Many plants can cause either irritant or allergic skin rashes. The single most common cause of allergic skin reactions in the United States is contact with poisonous plants such as poison ivy, poison oak or poison sumac, according to the American Academy of Dermatology. Common house and garden plants (including daffodil, chrysanthemum, sunflower and dandelion) can also cause allergic skin rashes in sensitive people.

The parts of the plant that cause the allergic reaction or irritation vary and include hairs, sap, oils, leaves, stems, petals, roots and bulbs. Outdoor plants, both weeds and native varieties, may cause allergic and irritant skin rashes. Plants with thorns, such as stinging nettles and thistles, are well known for irritating the skin.

Rashes caused by an allergic reaction to plant parts are called allergic contact dermatitis. Rashes caused by irritation due to plants are called irritant contact dermatitis. Plant dermatitis can result from direct contact with a plant, indirect contact with a plant (such as touching something that touched the plant) or contact with airborne plant particles that are either inhaled or come into contact with skin. Some plants (e.g., limes, wild parsnip) only cause a reaction when sunlight is present on the skin at the moment of contact. In such instances, touching the plant produces a chemical reaction between plant compounds and sunlight (phytophotodermatitis).

Any plant may cause an allergic reaction in a sensitive person, but the most common sources of plant rashes are poison ivy, poison oak and poison sumac. According to the American Academy of Dermatologists (AAD) 10 million to 50 million Americans develop an allergic rash after contact with these poisonous plants. Characteristics of these plants include:

• Poison ivy. A weed with three shiny green leaves and a red stem, it typically grows in vines and can be found along riverbanks. Resins of these plants cause a reaction in many people when their skin comes into contact with the plant. In addition, smoke from burning poison ivy plants can cause the same type of skin rash in people exposed to the smoke. Poison ivy is found throughout the United States except in the Southwest, Alaska and Hawaii. In some areas – such as in the far northern and western United States, the areas around the Great Lakes, and Canada – poison ivy grows as a shrub.
  
  
• Poison oak. Has the same three-leaf structure as poison ivy, but grows in the form of a shrub in the eastern United States and a shrub or a vine in the western United States. It is found primarily on the West Coast.
  
  
• Poison sumac. Grows as a woody shrub, with each stem containing seven to 13 leaves arranged in pairs. It grows in standing water in the peat bogs of the Northeast and Midwest and in swampy areas of the Southeast. It grows most abundantly along the Mississippi River, but can also be found less commonly in other regions.

All three of these plants irritate the skin through their resin, an oily sap known as urushiol that sticks to just about everything it comes into contact with. Urushiol is a nearly invisible colorless or pale yellow oil that oozes from cut or crushed roots, stems and leaves.  The rash itself is not contagious, although there is a slight chance that a person can be affected after coming into direct contact with resin that remains on another person’s skin or on clothing, pets or other objects.

Plants that are part of the same family (based on common features and similarities in structure) can create similar allergic reactions. For instance, onions are in the same family as lilies because of the type of root they share (a bulb) and their similar leaf structure. Yet onions have unique flavor characteristics that other plants in the lily family do not have. Nevertheless, someone who is allergic to lilies is advised to avoid onions, garlic, hyacinth, tulips and other plants in the same family. Lily sap can trigger an allergic skin rash and the rest of this plant family may cause an allergic rash in people with lily allergies.

Families of plants will include a wide variety of plants that do not look or taste similar (on casual examination) but share important characteristics that make them scientifically comparable. For example, a person who is sensitive to poison ivy, oak or sumac may also have reactions to latex (rubber) and to mango, cashew, celery, carrots and fig plants. This is because they are all from the same plant family.

The sensitivity people have to poisonous or irritating plants varies from person to person. A person's sensitivity to plants also tends to decline as they age.

There are two basic forms of plant rashes that affect the skin: allergic or irritant. Both are forms of contact dermatitis. Allergic contact dermatitis occurs when a sensitive person comes into contact with a plant or plant part (such as lilies or poison ivy) that acts as an allergen (a substance that triggers an exaggerated immune system response). The rash develops as part of the allergic reaction to the allergen.

Because allergic contact dermatitis involves an allergic reaction, an initial exposure to these plants rarely produces symptoms. The skin first must become sensitized to the resin released from these plants before symptoms appear. In addition, sensitivity to the resin of these plants tends to decline with age.

Allergic skin reactions can also be triggered by burning plants that cause allergic rashes. For example, poison ivy plants have oil called urushiol present in all plant parts. This oil may trigger a severe allergic reaction in people that breathe in the burned plant particles. The small burned particles can be inhaled and cause allergic contact dermatitis inside the nose, throat and lungs.

Irritant contact dermatitis occurs when someone comes into contact with a plant or plant part that irritates the skin, causing a rash. Stinging nettles are a good example of a plant that will cause an irritating rash in most people. Irritant contact dermatitis does not require developing a sensitivity to the plant.

In most cases, symptoms associated with plant dermatitis will appear within two days of exposure, although they may appear as late as two weeks after exposure. Urushiol (the resin of poison ivy, oak and sumac) begins to penetrate skin within minutes, although it takes longer to penetrate thicker skin such as that of the forearms, legs or trunk (torso). The following signs are characteristic of plant-induced contact dermatitis:

• A rash will appear between four hours and 10 days after exposure to the plant, depending on individual sensitivity to the plant and the amount of contact. The rash is typically asymmetrical and often appears in a pattern of streaks or lines that are consistent with where the plant came into contact with the skin. Rashes typically develop on thin areas of skin earlier than thicker areas (e.g., forearms, legs, trunk) due to faster absorption of plant sap and oils in skin that is thinner.
  
  
• Redness and swelling occur at the contact site, often followed by blisters and severe itching.
  
  
• In a few days the blisters may become crusted and begin to scale.
  
  
• The rash may take 10 days or more to heal on its own.
  
  
• The rash affects any part of the body, but especially areas of thin skin, such as the face.
  
  
• The rash does not usually spread on its own but can be spread through renewed contact with plant sap or oils from unwashed clothing, tools or an animal. The fluid found in blisters cannot by itself spread the rash.

Though rare, plant-related rashes may be accompanied by symptoms involving another body system, such as difficulty breathing. Reactions involving two or more body systems are called anaphylaxis and can progress rapidly to the potentially life-threatening anaphylactic shock. Therefore, people experiencing additional signs or symptoms along with a skin rash (e.g., runny nose, itchy eyes or shortness of breath) are advised to seek immediate medical attention.

Immediate medical care also should be sought for the following:

• Exposure to smoke from a burning plant such as poison ivy, poison oak or poison sumac.
  
  
• A rash that covers more than a quarter of the body, or that affects the face, lips, eyes or genitals.
  
  
• A rash that shows signs of infection, including pus, yellow fluid leaking from blisters, odor or increased tenderness.
  
  
• Fever of 100 degrees Fahrenheit (38 degrees Celsius) or more.

People who have experienced plant-induced skin rashes before will be familiar with the signs and symptoms of the condition and may not need to consult a physician. People experiencing a plant rash for the first time should consult a physician.

Common skin rashes that result from exposure to poison ivy, poison oak or poison sumac and do not require a visit to a physician can be treated with the following steps:

• Following exposure, wash skin thoroughly with soap and warm water as soon as possible. Skin that is washed within 30 minutes after exposure may not react to the urushiol resin. Wash clothing and shoes with soap and hot water, as resin can linger on such surfaces for days.
  
  
• Scrub under the fingernails to remove any resin that might be transferred to other areas of the skin through touching or scratching.
  
  
• Bathe pets exposed to resin to eliminate the substance from their fur.
  
  
• Keep cool by applying cold compresses to the skin or taking cool showers. Body heat and sweating can aggravate itching. Soaking in a lukewarm bath with an oatmeal or baking soda solution also can help relieve itching and help to dry oozing blisters.
  
  
• Use of some over-the-counter medications (such as calamine lotion or antihistamines) can help reduce symptoms. Patients should not use any medication without first consulting a physician.

To diagnose plant dermatitis, physicians will perform a complete physical examination, and collect a medical history that addresses:

• The history of the condition
• Any family history of skin rashes
• Potential exposure to poisonous plants
• When the rash first occurred

Once a diagnosis of a plant rash has been made there are a number of treatment options. The severity of the rash will be a deciding factor in the recommended treatment. Usually plant rashes are not severe and are best treated with a soap and water wash followed by calamine lotion to relieve any itchiness. Cool baths containing oatmeal will also help to soothe the skin. Because body heat and sweating can trigger itchiness, patients may also benefit from taking cool showers and applying cool compresses to their skin.

For severe plant rashes the physician may recommend over-the-counter or prescription medications. Medications that may be used to treat plant rashes include:

• Corticosteroids. Anti-inflammatory medications similar to the hormones produced by the body that help reduce swelling, redness and itching. For plant rashes, creams or ointments are applied to the affected area(s). Very severe rashes may require injected or oral corticosteroids.
  
  
• Antihistamines. Medications that block the effects of histamines (chemicals released during an allergic reaction that produce symptoms such as running nose and sneezing).
  
  

  

• Antibiotics. May be prescribed for severe rashes that have become infected.

It is important to note that symptoms may continue to appear after treatment has begun. This is the result of the allergen spreading to other areas of the body through the bloodstream.

The primary and best method of preventing a plant rash is to avoid poisonous or irritant plants. The following recommendations will help to prevent or limit skin contact with these plants:

• Wear protective clothing that adequately covers the entire body when spending time outdoors. This includes long pants, shirts with long sleeves and boots.
  
  
• Learn the appearance, life cycle and habitat of poisonous plants in the region.
  
  
• Use caution with unknown plants.
  
  
• Wear gloves when gardening or performing other activities with plants.
  
  
• Be aware of the potential for house and garden plants to induce an allergic skin reaction and avoid cultivating those species, or use extreme care when in contact with these plants.
  
  
• Shower after spending time outside.
  
  
• Wash clothing after spending time outdoors to remove any sap or oils from poisonous plants that may have adhered to the fabric. If contact with a poisonous or irritating plant is suspected, clothing should be washed outside with a garden hose or immediately washed with detergent in a washing machine. Clothing brought indoors should not be placed on rugs or furniture.
  
  
• Do not burn potentially poisonous plants or plant parts. Some poisonous plants like poison ivy, poison oak and poison sumac may cause severe allergic reactions if the plants are burned and the particles are breathed into the airways.
  
  
• Wash all tools or pets that may have come into contact with the poisonous plant with soap and water. This is important because the oil in poisonous plants (urushiol) can stay active for a few years.
  
  
• A rash from poisonous and irritant plants can also be prevented by washing the affected part of the body with soap and water within five minutes of contact with the plant. Washing with soap and water within 30 minutes of plant contact will also help prevent a rash from developing or spreading to other areas of the body. People who suspect contact with a poisonous or irritant plant should avoid taking a bath. This could allow plant saps or oils to enter the bath water and spread to other areas of the body. Showering with soap is a better alternative.

Though avoidance is the only completely effective method of preventing plant rashes, it is not always possible. Barrier skin creams may provide an additional layer of protection for some patients. These creams are applied to the skin before contact with the plant to create a barrier between the plant particles and the skin surface. Because the particles do not come into contact with the skin, a rash is not triggered.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about plant dermatitis:

1. Do my symptoms suggest plant dermatitis?
   
   
2. Can I spread my rash to other people or to other parts of my body?
   
   
3. Is my plant rash severe? Will I require medication?
   
   
4. When will my symptoms subside?
   
   
5. How can I prevent exposure to sources of plant dermatitis?
   
   
6. Can you give me a list of plants that commonly cause plant dermatitis in this area?
   
   
7. Are there steps I can take to prevent symptoms once I have been exposed to these plants?
   
   
8. How can I prevent a secondary infection from developing?
   
   
9. When should I seek medical attention for plant dermatitis?
   
   
10. What at-home treatment methods can I use to treat plant rashes in the future?