Typically, one to three days after contact, a red line of small bumps appears where the sap penetrated the skin. The bumps later become blister-like vesicles, which weep if broken. New rashes can crop up in different areas, not because the rash itself is contagious, but because the sap was in contact with other areas in different concentrations, or simply because it took longer to penetrate thicker-skinned regions.
If poison ivy seems to recur every few weeks, it is most likely due to repeated contact with the oil. Sap can remain on clothes, sports equipment, the fur of a family pet, even on firewood.
Avoiding a Rash
Know what the plants look like in your area and teach kids where and what they are. Since the oil turns black in air, avoid plants with black spots on them. Of course, most exposure is accidental, and you can wash the affected area in the first few minutes with soap and water or hydrogen peroxide to help remove some of the oil before it penetrates the skin. Pay particular attention to scrubbing under the nails, and wash clothes that may be contaminated with sap, as well as balls, tools, even pets. Finally, wear vinyl gloves when gardening or weeding.
Once the rash presents itself, there is no cure, only efforts to relieve the symptoms. Fortunately, poison ivy and related plant rashes do go away on their own, after about two weeks. Steroid creams and ointments, applied before the blister phase, help quench the reaction, but the over-the-counter preparations may not be strong enough to have much effect. Cool compresses, oatmeal pastes, calamine lotion, and some herbal remedies all provide a soothing effect. In severe cases, oral steroids are used briefly (five to seven days) to dampen the inflammatory response. Antihistamines like diphenhydramiine (Benedryl) offer only a better night's sleep fromm the misery of itching through their tendency to make most children sleepy.
Though not scratching a rash like poison ivy can be very hard, the less the broken skin is traumatized, the lower the chance of another skin infection developing. Keeping fingernails short and clean is a way to reduce the chance of introducing germs into the skin when the inevitable scratching occurs. If a rash later becomes an angry red, very painful, or if a fever develops, a second infection may have occurred and an antibiotic may be necessary.
Overall, if a plant such as poison ivy can be identified in advance, it is best to walk away, and "leaf" it at that.