Poison Ivy

• Poison ivy is a plant that often blends in with other vines or weeds in the undergrowth. Between 6 and 30 inches tall if it grows from the ground, or much longer if it grows like a hairy vine up a tree, both versions of poison ivy have stems with three leaves. This has given rise to the common saying, "Leaflets three, let it be."
  
  

Rash

• Most people who come into contact with poison ivy will develop a rash. This is because the plant secretes an oil called urushiol. When a person touches poison ivy, this oil will bond with the person's skin and cause irritation, and the itchy, unpleasant side effect of poison ivy rash.
  
  

Initial Appearance

• The rash caused by poison ivy is usually red and extremely itchy. The first symptoms of it will appear between one and two days of the urushiol oil bonding with the person's skin. However, it's also very important not to scratch the affected skin so as not to spread the rash.
  
  

Blistering

• A day or so after the redness and swelling of the initial rash, small blisters will begin to form on the rash. Scratching these blisters may cause infection, so someone suffering from poison ivy should make sure not to do so.
  
  

Duration

• Generally speaking, a poison ivy rash will only last for about a week from the initial swelling and redness. However, if the area of skin that's affected is relatively large then the rash may last longer. The symptoms won't change though, no matter how large the rash is.