Counterknowledge. No - not a new word for arithmetic, or the things you need to know to be a successful shop assistant. Counterknowledge, according to Damian Thompson, is "misinformation packaged to look like fact." Apparently we are a gullible bunch and can be persuaded that all sorts of things are true, and it can be blamed on muddled gathering of evidence.
Thompson tells us that counterknowledge is behind conspiracy theories from Dan Brown to Diana, but also exists in health. Everything from belief in the usefulness of fad diets to a fear that MMR causes autism might be defined as counterknowledge.
Half truths work best when based partly on truth - there has to be a grain of credibility to start with. The best urban legends are always stories that happened to someone that you have some connection with. The story teller will also assure you it must be true because it happened to their next door neighbour's best friend's cousin. Even hoax emails tend to be prefaced with "my friend at BigCorporationBank sent this to me" or are apparently originated by a bigwig at Microsoft, Hotmail or elsewhere. We feel better disposed to trust something that comes from a source that is known to us.
Sometimes we believe because we want to hope, especially when we are sick. We want to believe that Aloe Vera, omega 3, coenzymes and carrot juice cure cancer if the alternative is to believe that we are going to die.
Health professionals are not immune to being hoaxed. We must all think as we read and question what we hear. I've mentioned CASP before, which helps you ask questions around evidence you find. The other important thing is to take care where you collect your evidence from. The National Library for Health, Intute, PatientUK, reputable charities are all a better start than the open web for good quality information - clean, clear knowledge. Oh - and did I mention that libraries can look for quality information for you and your patients?