Cat Coat Composition

The cat has three types of hair:

1. Guard hairs - part of the top coat. This is a protective coat to the undercoat and the hair strands have a sensory function. They are straight and taper to a fine point. They are the longest of the three types.
2. Bristle or awn hairs - part of the top coat. They form a protective coat to the undercoat and have a sensory function. They are thinner than guard hairs but variable in thickness. They thicken near the tip before tapering to a point. They are intermediate in length between guard and down hairs.
3. Down or wool hair - undercoat. They serve as an insulating barrier against heat loss. These are the thinnest and finest and of similar diameter throughout their length.

To which can be added:

1. Whiskers (vibrissae)- these are very sensitive and play an important sensory role when travelling in dark conditions and are used to feel prey when killing prey.

The above is the classic coat structure for long haired cats but some cats have single coats. You will see coats lying flat to the body with no undercoat. This is easy to see using a comb and it is easy to comb even with a flea comb. Double coats can be hard to comb if left unmaintained. The Siamese and Siamese related cats have single coats as has the Devon and Cornish Rex which have fine curly hair. The rex cats shed less than normal coated cats but the Devon Rex can be semi-bald on occasions.

Double coat - thick and "sticky". Photo by rlihm

The American Wirehair has a "tightly crimped coat" that is coarse to the touch.

When a cat's hair grows for a longer time it becomes long hair. When the rate of growth is slower the hair become very short as for the Cornish Rex. In the case of the Cornish Rex the rate of growth is normal.

The three types of hair strand narrow where they enter the skin and then thicken under the skin (subcutaneously) forming a club, which anchors the hair strand.

New hairs are created throughout the year replacing old but seasonally this process reaches a peak in late summer says Robinson's Genetics. An alternative view¹ is that cats who spend all the time outdoors shed most in late spring while cats who go out for part of the day shed at the beginning of summer. Indoor cats may shed more lightly and year round.

Mid-winter is the time when molting is at its slowest. The molting process is dictated by the amount of ambient light and not temperature. More ambient light results in more shedding. 

A male cat's seasonal molt is about two months in advance of a female's. Neutering has no effect on molting. Winter hairs are slightly longer than summer hairs.

When double coated cats begin to shed, the down hair sheds patchily. Brushing a cat during shedding helps remove the dead hair.

We know that the pointed cats are temperature sensitive which creates the pointing. The darker extremities are cooler than central parts of the body. It is possible to create localised darker areas in a Siamese cat.

Note: 1. Cat Owner's Home Veterinary Handbook.