Rash from poison ivy. Many people develop an itchy rash that causes lines or streaks that look like this. Poison ivy, oak and sumac: Overview Many people get a rash from poison ivy, poison oak, and poison sumac. This rash is caused by an oil found in the plants. This oil is called urushiol (you-ROO-shee-all).

  Hives: An allergy to a medicine can cause hives. Hives: Overview Also called urticaria  Hives are welts on the skin that often itch. These welts can appear on any part of the skin. Hives vary in size from as small as a pen tip to as large as a dinner plate. They may connect to form even larger

Bedbugs: Overview Bedbugs are tiny insects that feed on human blood. They hide in dark places close to where humans sleep and usually crawl out to feed while people are fast asleep.   Bedbug bites: Most people who are bitten by bedbugs have welts that look like these shown above. Bedbugs can be