The skullcap is symbolic of the surgical profession. The skullcap can be worn when close to the totality of hair is covered by it and only a limited amount of hair on the nape of the neck or a modest sideburn remains uncovered. Like OR scrubs, cloth skullcaps should be cleaned and changed daily. Paper skull caps should be disposed of daily and following every dirty or contaminated case.
The Association of periOperative Registered Nurses (AORN) responded with a statement of its own:
Several types of evidence exist that support recommendations that perioperative personnel cover their head and ears in the OR. This evidence includes the fact that human skin and hair is naturally colonized with many bacteria, and perioperative personnel shed microorganisms into the air around them. We know airborne bacteria in the OR can fall into the operative field, contribute to the overall air contamination of the OR, and place patients at risk of surgical site infections. Completely covering the hair can reduce the number of bacteria introduced into OR air by perioperative personnel.
Unfortunately, the "evidence" cited by the AORN is all circumstantial. Yes, human hair and skin may be colonized with bacteria. There is no proof whatsoever that a single surgical patient has ever been infected by a hair or skin droppings from OR personnel. If you want to extend this logic to its inevitable conclusion, the entire neck and face should be covered too. Eyebrows and eyelashes could be deadly. Maybe all OR personnel, including circulating nurses and anesthesia, should wear helmets like those used by astronauts or deep-sea divers.
Perhaps the AORN should get its own house in order first. Many of the OR nurses and techs that I have worked with over the years wear their supposedly fully covering headgear like this: