Acupuncture is a collection of procedures involving penetration of the skin with needles to stimulate certain points on the body. Research suggests that traditional forms of acupuncture are more effective than placebos in the relief of certain types of pain and post-operative nausea. Acupuncture needles are typically made of stainless steel wire. The skin is sterilized, e.g. with alcohol, and the needles are inserted, frequently with a plastic guide tube. Needles may be manipulated in various ways, e.g. spun, flicked, or moved up and down relative to the skin.