Poison ivy, oak, and sumac do not 'spread:' the skin just takes longer to react in some areas that don't have as much urushiol on them. It appears that it is 'spreading,' when it is, in fact, a delayed reaction.
After the fact, calamine and oatmeal seem to work best for us. When outdoors in areas with poison ivy (learn what it looks like in your area-there are many variations of leaf notching), when you come inside wash immediately with soap and / or shampoo with cool water. Hot water will open up the pores and drive the oil deeper, making worse blisters. Don't use alcohol, it will drive the oil deeper also. Once the rash appears, hot showers can overload the 'itch' sensation for a while. The oil has already been absorbed by the skin, the heat won't make it worse. For any secondary infections from scratching, mist as often as you think of it with CS, or if it is a larger area, cover with a cotton pad soaked in CS or CS gel.
