A typical rash from poison ivy, oak and sumac starts with itchiness and swelling, followed by a reddish inflammation of tiny pimples. After this, blisters form and couple in a chain-like reaction. It is common for a clear fluid to ooze from the blisters.
Note that it is a common misconception that the fluid causes the rash to spread. The only way a poison ivy rash will spread is if the plant's urushiol spreads to other parts of your body.
The fluid from the blisters then hardens to a yellowish crust. Left untreated, poison plant rash (a typical histamine response) will last three to five weeks.