Just thinking about poison ivy can make you itch. Blistering rashes on your arms and ankles, oozing bumps between your fingers and eyelid-swelling exposures are all-too-familiar summer hazards.

You're working in your garden, pulling weeds and making sure everything looks pretty. A few hours later, while admiring your garden, you start to feel an itch on your arm and notice some red bumps. At ...