What is the undercoat?
Most cats actually have double coats. The exception is the single-coated Rex that sports fine, curly hair and does not shed. A double coat is made up of an outer “guard” layer that is longer and coarser. The lower layer is very soft, and fine. That is the undercoat.
Guard hairs are single and have individual follicles. The undercoat is more like clumps, and when those clumps become tangled with masses of guard hairs, a dense and painful mat forms. These tangles lie close to the skin and tug at the undercoat when the animal moves. They are both difficult and dangerous to remove and should never be cut away for fear of harming the animal’s delicate skin.
Not all cats shed the same way. As a general rule, cats who spend all or some time outdoors will shed seasonally, while indoor cats shed all the time. This is not true across all breeds, however. Any time that a cat sheds his dense undercoat, he is more likely to get mats and the regurgitation of hairballs will be more prevalent.
In cats who have a thick undercoat, surface brushing will not sufficiently remove dead hairs to keep the coat as a whole in good health and appearing well groomed. Wire brushes are good for reaching the undercoat, as are special tools called undercoat “rakes.”
It’s important never to tug at a cat’s fur while grooming, however. When brushing to remove dead hair and thin the dense undercoat, always pause to take accumulated hair out of the brush or comb. Leaving them in will only encourage the fur to mat.
Brushing improves the health of the cat’s entire coat, cuts down on instances of vomiting hairballs, prevents matting, and lessens the amount of shed hair around the house. It is important, however, to brush thoroughly, tending to both the surface guard hairs and the thicker, softer undercoat.