Masks are used to change the appearance. Masks come in a very large variety, ranging from gas masks to carnival like masquerades.

Hoods are the classic form of head harness. Usually made of leather or latex, they can be made as one piece completely covering the head or with holes for eyes and mouth. The later form is usually combined with blindfolds.
Some hoods also integrate a piece of material extending the chin to give the wearer a puppy or pony like appearance.

Head gear is often used to keep blindfolds in place. This usually consists of one strap under the chin and another one across the forehead or over the head.

Gags are also often combined with head gear to keep the wearer from being able to eject the gag from his mouth.

Head harnesses can be made of many different materials. Leather, latex and rubber are most common materials but cloth, rope and others can be found. When selecting the material for a head harness keep in mind that the skin on the head is usually much more sensitive than on other parts of the body.

Many pieces of head gear are made purely for looks. This is obvious in animal, devil and other masks.

One common use for head gear is for immobilisation of the subject. This is usually done by tying the headgear with rope to stationary objects or to other pieces of bondage equipment like leather cuffs or a ass hook.

Head gear is often combined with blindfolds. This keeps the blindfold securely in place.
Another form of vision restriction are blinders, commonly used in pony play.

Head gear is often used to keep gags in place. This is often indicated by using the word “training” in front of the name of the gag - i.e. a training bit is a bit style gag that has additional head gear to keep it in place more securely.