The gene that causes hairlessness also results in the breed often having fewer teeth than other breeds, mostly lacking molars and premolars. All are born with full sets of puppy teeth, but these are not fully replaced by adult teeth as they naturally fall out, leaving them with varying levels of adult dentition. The hairlessness trait is a dominant double lethal mutation, which means that homozygotic hairlessness does not exist. Homozygous embryos, those with two copies of the gene, do not develop in the womb. This results in an average birthrate of 2:1, hairless : coated. According to Hans Räber "Enzyklopädie der Rassehunde" T.I 33% of the population is born coated.
While they are recognized by the American Kennel Club (AKC) for its Foundation Stock Service as Peruvian Inca Orchid dogs, they cannot be shown at AKC shows, they are also registerable with FCI, UKC, NKC, APRI, ACR. Some breeders think that interbreeding with coated (Peruvian) dogs is required to maintain functional teeth and nervous system health in subsequent generations. They say that breeding of hairless with hairless (and common but unacknowledged culling of hairy pups from litters to maintain a "pure" image) leads to short-lived dogs with serious health problems. However, other breeders (especially in Peru) think the opposite, and are doing well (for centuries already), too. Peruvian non-breeder families typically out-breed with coated dogs every other or every third generation to keep them healthy.
Like all breeds there are some health problems. These include IBD, seizures, stroke, and skin lesions. They are very sensitive to toxins and care should be taken in use of insecticides. Insecticides are absorbed through the skin, and body fat keeps these toxins from entering the liver too quickly. Since these dogs have very low body fat, toxins are absorbed too quickly and cause severe damage to the nervous system and GI tract.