All burns cause injury to the skin, which consists of three layers of tissue: epidermis, dermis, and subcutaneous. The surface of the skin is the epidermis, which is the layer that is always damaged or missing in a burn injury.
Deeper burns can extend into the dermis, where most of the nerve endings and hair follicles are located. The deepest burns extend into, or through, the subcutaneous, a layer of fatty tissue under the dermis.
Friction burns account for about 1% to 2% of all types of burns. Statistics on the different surfaces that cause friction burns—rug burns, road rash, treadmills, etc.—are not readily available. Anything that can rub off layers of skin can cause a friction burn.
Carpets or rugs are well-known culprits. A more modern growing cause of friction burn is the treadmill, which can be particularly damaging to kids. Luckily, in most cases, treatment is fairly straightforward.