If you use cold water to rinse before you use soap is the suggestion from the MO conservation Dept. The idea is that the water will rinse most of the oil off your skin. Although the original suggestion did not mention the temperature of the water used for washing I would suggest that the coolest you could stand would be best. Hot water will open your pores more than the cooler water.
The reason that you do not use soap first is that the soap not only breaks down the poison ivy oils but also your skin oils. If you do not rinse thoroughly the mixed oils could remain on the skin.
