Some claim drinking eight glasses of water a day leads to good health, while reading in dim light damages eyesight.
Others believe we only use 10% of our brains or that shaving legs causes hair to grow back thicker.
But a review of evidence by US researchers surrounding seven commonly-hold beliefs suggests they are actually "medical myths". Some are utterly untrue, while others have no evidential proof, the British Medical Journal reports.
Researchers from the Indiana University School of Medicine in Indianapolis hunted medical literature for evidence on each claim.
They found no evidence supporting the need to drink eight glasses of water a day.
In fact, studies suggest that adequate fluid intake is often met by drinking juice, milk, and even caffeine-rich tea and coffee.
Data also suggests drinking excessive amounts of water can be dangerous.
The belief that we only use 10% of our brains appears to be completely untrue.
Source - BBC