Combing to the Skin
All dogs should be combed to the skin. If the undercoat is thick and you can't get a comb through it, then air can't get to the skin. This creates a breeding ground for bacteria, and it inhibits the coat and skin from drying when the pet gets wet. Thick coats that are packed with dead undercoat get wet and can't dry, and this leads to skin infections. In addition, if the undercoat is packed and wet, the dog can't get dry and it's like wearing a wet wool blanket. If it's cold out and his coat is wet, he can suffer hypothermia. If it's summer, then air can't reach the dog's skin to cool it down, which is why most dogs shed more in the spring and summer.
Combing to the skin is one thing most pet owners neglect to do because they feel they are hurting the dog if they pull on any hair. You can brush the topcoat out to make it look nice, but the hair is knotted underneath. If you brush the top but you can't get a comb through the coat, you defeat the entire purpose of brushing the dog. It's better to begin line brushing the dog first, using a pin brush or slicker brush, then work your way down to fine-tooth tools such as combs.
Don't dry brush or comb a dirty dog; make sure the hair is clean first. Clean, dry hair is okay to comb or brush, but dirty, dry hair will break off and you will damage the hair shafts. Wet hair will stretch and not break as easily. This preserves the coat and makes the dog look better. However, you can overstretch wet hair and snap it off, which causes damage as well.
One example of the difference good brushing can make is the Afghan Hound. Forty years ago, Afghan Hounds in the show ring had shorter coats; today, the coats almost reach the floor. Brushing technique and enhanced products protect the hair. Most groomers today know that dry brushing a dirty dog will break off the hair. Groomers should make sure they thoroughly wash, condition, and dry each dog before using any tools on them. Dogs brushed out between baths should always be sprayed with a conditioning spray before brushing to preserve and protect the hair.