This is a interesting question. It is certainly peculiar that we are seeing many hairless cats with incredibly wrinkly skin particularly on the top of their heads. I’m not sure that there is a caste iron answer to the question as to why hairless cats have wrinkly skin. Certainly, cats with fur do not have wrinkly skin to the same extent. Important: it is very variable. Some Sphynx and Don Sphynx cats don’t have a lot of wrinkly skin. This may help in answering the question. And there will be some natural wrinkling when the body moves as skin is elastic and it will bunch up.
However, it does not take a lot of work to find out that your domestic cat companion, sitting on your lap, has a smooth forehead. All you have to do is part the fur on the forehead and have a peek. It is certainly smooth. There is no reason why it should not be smooth. And there is no reason, on the face of it, why the hairless cat breeds should have heads which look as if their brain is exposed! You know the look that I mean: the skin is so crinkly it looks like the folds of the brain.
I can’t find an answer on the internet so I’m going to speculate. There are three different things about the hairless cats in connection with their skin: the hairlessness is caused by a genetic mutation, their skin is exposed to the elements and it needs to be constantly cleaned.
The mutated gene causes the hair follicles to stop producing hair strands. Does this gene affect the amount of fat in the epidermis of the skin? Does the gene affect the elasticity of the epidermis and dermis of the skin? I think these are the sort of questions that one should be asking.
I suspect that the mutated gene has an impact not only on the production of hair strands but on the production of the tissues that make up the skin of the cat.
In addition, the fact that the skin is exposed to the elements may also be a contributing reason. Perhaps it causes the skin to dry out. This is another issue because people who own Sphynx cats have to clean their cat regularly because the sebaceous glands in the skin deliver oils which have nowhere to go except to be deposited on the skin surface. This attracts dirt which needs to be wiped off. Perhaps it is this constant cleaning of the skin which contributes to the skin losing its elasticity or moisture which in turn causes it to become wrinkly. As I said, I am speculating to try and find an answer.
The degree of wrinkliness is quite variable. Some hairless cats look incredibly strange because of this unusual skin defect as I would call it. While in other cats it is not so pronounced.
If you have any ideas on this I would be pleased to hear them in a comment.