Keeping a wound covered helps it heal faster. That is why a doctor covers a wound with a wound dressing. The dressing supplies the right balance of moisture required for healing and enables the beneficial bacteria to function and thus, prevents infection. The healing cells are also able to cover the wound with new smooth tissue faster. Covering a wound also reduces the chance of scarring. It helps prevent scabbing, as well as protects the wound from the sun. The earlier belief was to let a wound be exposed to the air and allow a scab to form. But the scab can slow the healing process. And on falling off, it leaves a visible mark.