A_ degree burn is when all layers of skin are damaged

Fourth

Explanation:

A fourth degree burn is when all layers of the skin are damaged. A third degree burn burns into the fat layer, while a fourth degree burn burns through all the layers of the skin. In both cases, immediate medical help is needed.

3rd degree burn

Explanation:

A first degree burn effects, you guessed it, the first layer of skin, the epidermis.

A second degree all the way down to the dermis, the second layer.

A third degree burn effects all layers of skin down to the tissues below.

A fourth degree burn is a subset of a third degree, but it implies that it goes all the way to the muscle or bone.