A motorcycle helmet must meet DOT gauges to be legitimate for the street, a snowmobile head protector does not.
You could, but you will keep your head warmer if you wear your beanie UNDER your helmet.
If you fall and hit your head on the sidewalk, a helmet will keep you from busting your head open. If you fall of a bike and land on your head, a helmet will protect you head.
Full face snowmobile helmets and motorcycle helmets both protect the riders head and face from injury and the elements and can be used interchangeably. The only difference is that some snowmobile helmets have a breath box to keep the face shield from fogging up. I got my helmet from rideinstylehelmets.com.
Beards are not in the helmet. Only the upper portions of the head are in the helmet.
If you fall off and hit your head serious injury can occur.
If you hit your head on something, the helmet will spread and soak up some of the energy of the hit, reducing your risk of head injury. If you don't hit your head, the helmet won't do anything. In extremely rare cases, the helmet will snag on something and yank on your head/neck.
A lump on the back of your head that is itchy may be from an inset bite. If the lump does not go away, visit a doctor.
things in your hair that are make it itchy are probably head crabs
Helmet
A helmet is a head gear that was worn by the Greek soldiers. It was meant to shield the head against attacks from enemies.
Wearing a bicycle helmet can greatly decrease the risk of head trauma. Other injuries on bicycles will not be affected by helmet use. The helmet is there to protect the head.