Applying a wet compress or soaking the affected area in cool water reduces the itch associated with poison ivy rashes, according to WebMD. The compress can be made out of a paste of baking soda or vinegar mixed with water.
Taking cool, short baths with an oatmeal additive may also relieve the itch of poison ivy, states WebMD. Keeping the area moisturized by applying lotion when the area is damp is also recommended. Over-the-counter antihistamines, such as Benadryl, can relieve itching. Finally, applying antihistamine or hydrocortisone cream can help after soaking the affected area in water or after applying a compress.