Wikipedia: "Tecnu is an over-the-counter skin cleanser manufactured by Tec Labs, a pharmaceutical company based in Albany, Oregon. It is intended for use by humans and furry pets after topical exposure to urushiol, the active ingredient in poison oak, poison ivy, and poison sumac.[1] Tecnu is made from deodorized mineral spirits, water, propylene glycol, octylphenoxy-polythoxethanol, mixed fatty acid soap, and fragrance.

The cleanser was invented by former Mead Johnson executive and chemist Dr. Robert Smith during the early 1960s. Tecnu, for "Technically New," was intended to remove radioactive fallout dust from skin. Several years later, his wife discovered another use for the cleanser. After an exposure to poison oak, she washed with Tecnu and did not get urushiol-induced contact dermatitis.[2]"

Small bottle of mineral spirits plus dr. Bronners should be a rough equivalent. Handy for fallout, too.

I recently read where rubbing bar soap on a mosquito bite will help the sting.