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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.