Looks like maybe I posted some bad information. I swear, years ago I looked at the Merck Manual and it said blister fluid was self contagious. Maybe I've smoked too much dope, or maybe the science has been updated. Whatever the case here's some info from the Mayo Clinic:
When your skin touches the leaves of the plant, it may absorb some of the urushiol made by the plant. It takes only a tiny amount of urushiol to cause a reaction. Urushiol is very sticky and doesn't dry, so it easily attaches to your skin, clothing, tools, equipment or your pet's fur. You can get a poison ivy reaction if you:
- Directly touch the leaves, stem, roots or berries of the plant, shrub or vine.
- Unknowingly rub the urushiol onto other areas of your skin. For example, if you walk through some poison ivy then later touch your shoes, you may get some urushiol on your hands, which you may then transfer to your face by touching or rubbing.
- Touch urushiol left on an item, such as clothing, firewood or even a pet's fur (animals usually aren't affected by urushiol). Urushiol can remain allergenic for years, especially if kept in a dry environment. So if you put away a contaminated jacket without washing it and take it out a year later, the oil on the jacket may still cause a reaction.
- Burn the plants and inhale the smoke. Even the smoke from burned poison ivy, poison oak and poison sumac contains the oil and can irritate or injure your eyes or nasal passages.
A poison ivy rash itself isn't contagious. Blister fluid doesn't contain urushiol and won't spread the rash. In addition, you can't get poison ivy from another person unless you've had contact with urushiol on that person. The reaction usually develops 12 to 48 hours after exposure and can last up to three weeks. In severe cases, new areas of rash may break out several days or more after initial exposure. This may seem like the rash is spreading. But it's more likely due to the rate at which your skin absorbed the urushiol.
That last line doesn't make any sense to me based on personal experience, but whatever... I'm no doctor.