Why is a helmet that meets the DOT standard the most important piece of protective gear?

A DOT-compliant helmet is the single most important piece of protective gear because head injuries are the leading cause of death in motorcycle crashes, and helmets are highly effective at reducing the risk of fatal and severe head and brain injury. A proper helmet fits snugly, is fastened securely, and meets the Department of Transportation safety standard (shown by the DOT label). A full-face helmet also protects the face and eyes. Riders should replace a helmet after any significant impact, even if damage isn't visible, because its protective foam may be compromised.