Sphynx cats are hairless due to a naturally occurring genetic mutation. This mutation affects the development of hair follicles and results in a lack of fur on their bodies. The hairlessness trait in Sphynx cats is a recessive gene, which means that both parents must carry the gene for their kittens to inherit the hairless trait, so breeders carefully select and pair cats with this gene to produce Sphynx kittens.