Itching

• Poison oak causes a maddening itch in affected areas. Ironically, scratching at it often spreads the oil around, making the itch worse.
  
  

Rash

• The skin affected by poison oak will become very red. The rash often has a linear shape, caused by brushing up against the plant.
  
  

Swelling

• Skin touched by poison oak will swell up, making it difficult to wear clothes or jewelry.
  
  

Blisters

• Poison oak causes blisters to break out in the affected area. Contrary to popular belief, the fluid emitting from blisters will not spread the poison oak infection further.
  
  

Time Frame

• The effects of poison oak appear anytime between 12 hours and two days after exposure, and often last for two or three weeks.