Why don’t Sphynx cats have hair?

The Sphynx cat, a breed known for its distinctive hairlessness, is more than just an unusual pet; it represents a unique case study in mammalian genetics. The breed’s hairlessness is not absolute; rather, it is characterized by a very fine down on its body, with some light and wavy hair often found on the nose, tail, and toes. This peculiar phenotype is primarily due to a mutation in the Keratin 71 (KRT71) gene, providing a fascinating look into the complex interplay of genes and traits.

To understand the genetic basis for the Sphynx cat’s hairlessness, it’s important to consider what hair is and its role in mammals. Hair, a characteristic structure of mammals, maintains body homeostasis, as well as facilitating cell and tissue integration. In the typical cat, the coat consists of three hair types: long guard hairs, thinner awn hairs, and fine undulating down hairs. Variations in these hair types contribute to the diverse range of pelage (coat) types seen in different cat breeds.

A mutation in the KRT71 gene, which codes for a protein expressed in the inner root sheath of hair follicles, is responsible for the hairlessness in Sphynx cats. This mutation is often referred to as the “hairless” (hr) allele. The KRT71 protein plays a crucial role in the formation of linear and normal Intermediate Filament (IF) proteins in the inner root sheath (IRS) of the hair follicle, which is crucial for hair shaft keratinization, or the process of hair formation.

When KRT71 is mutated, this process is disrupted, leading to the unique hair characteristics seen in Sphynx cats. Histological and dermatoscopic examination of Sphynx cat skin has revealed that their hair follicles are often small, curved, and kinked. They display a condition called hyperkeratosis, where the hair follicles become thickened, and dilation, where the follicles are expanded or enlarged. Moreover, the inner root sheath exhibits poorly defined layers and vacuolar-like changes, likely impairing the formation of proper hair shafts.

Furthermore, the hair shafts produced are typically misshapen, smaller in diameter, and lack a medulla, the innermost part of the hair shaft. Despite these abnormalities, the density of hair follicles in Sphynx cats is similar to cats with normal coats. This indicates that the mutation affects hair formation rather than the production of hair follicles. In essence, the Sphynx cat’s skin produces hair follicles, but these follicles fail to generate normal hair.

This mutation in KRT71 is not exclusive to cats. Previous studies in mice, rats, dogs, and cattle have identified KRT71 polymorphisms as responsible for curly or wavy hair phenotypes. In these other species, mutations often result in single amino acid deletions in the α-helical rod domain of KRT71, which is integral to the formation of hair structure.

The Sphynx mutation leads to a complete loss-of-function allele, affecting the structure of the hair. The phenotype of the Sphynx cat is likely dominant, meaning that if a cat has even one copy of the mutated KRT71 gene, it will exhibit the hairless phenotype. However, expression can vary, meaning that some Sphynx cats can have a small amount of hair in certain areas.

The absence of fur is not the only feature that defines the Sphynx breed. Sphynx cats are also known for their muscular bodies, large ears, and wrinkled skin, which further contribute to their distinctive look. These traits result from the interplay of several other genes, alongside environmental factors such as diet and care.

The mutation in the KRT71 gene that causes hairlessness in Sphynx cats is not harmful per se. Unlike some genetic mutations that can cause health problems, this particular mutation primarily affects the cat’s appearance, but does not have a significant affect elsewhere on the body. However, the lack of fur does mean that Sphynx cats require special care. For instance, they are more susceptible to cold temperatures and sunburn than their furry counterparts. Hence, owners of Sphynx cats need to take extra precautions to ensure their pets’ health and comfort.

The genetic diversity in cats, including breeds like the Sphynx, is a testament to the power of genetics. It shows how small changes in our DNA can have a significant impact on our physical characteristics. Moreover, the case of the Sphynx cat highlights the importance of understanding the role of genetics in pet health and care. Just as with humans, genetic knowledge can help pet owners and veterinarians predict potential health issues and provide the best possible care for these animals.

In summary, the hairlessness of Sphynx cats represents a fascinating case of genetics at play. The mutation in the KRT71 gene disrupts the keratinization process, leading to an apparent lack of hair. The hairlessness of Sphynx cats is just one example of how genetic mutations can shape the appearance and characteristics of a species. As we continue to explore the complex world of genetics, we will undoubtedly uncover more intriguing examples of how genes influence the diversity of life on Earth.


Gandolfi B, Outerbridge CA, Beresford LG, Myers JA, Pimentel M, Alhaddad H, et al. The naked truth: Sphynx and Devon Rex cat breed mutations in KRT71. Mamm Genome. 2010;21(9):509–15.
Genovese DW, Johnson TL, Lamb KE, Gram WD. Histological and dermatoscopic description of sphynx cat skin. Veterinary Dermatology. 2014;25(6):523.