Most people aren't afraid to use rubbing alcohol or hydrogen peroxide to disinfect a wound when they get a cut. According to WebMD however, using peroxide on a wound can actually harm the tissue around it and delay the healing process. This is just one first aid fallacy they're out to debunk.
They say instead a mild soap and cool running water are the best treatments for common wounds, and that you should rinse the wound for at least five minutes to remove it of debris, dirt or anything else that may be in there. The water will clean the wound out well enough for your body to take over without harming the still living tissue around the wound. If it's large, deep or bleeding a lot, they suggest heading to the ER or nearby urgent care facility.
The article goes into some other commonly held first aid beliefs as well, like using oil or butter to soothe burns (false,) that you should let scrapes and minor cuts "air out" (also false,) and that you should keep injuries moist to encourage healing (true.)