There’s a difference between tangles and mats. Tangles are loosely formed and usually occur in the outer “guard” coat. They don’t involve large areas and aren’t tightly clumped. For dogs who aren’t too sensitive, these can be brushed or combed out.
Mats occur when tangles get out of control. The hair clumps together tightly. They can form against the skin, under the top layer of hair. If you don’t brush your dog all the way down to the skin, mats can still form in the undercoat even if the outer layer of your dog’s coat looks good. Brushing out mats is time-consuming and very painful for your dog. It can even cause abrasions to your dog’s skin. Only shaving out matted areas is possible, but it will level the groom very untidy, due to the uneven hair length. To remove matted hair without hurting your dog, it’s necessary to shave the hair off close to the skin to get under the mats. This is the only way to remove mats without causing your dog any more pain. Continuing to shave the rest of the unmated hair allows the hair to grow back evenly.