Alopecia means hair loss of any degree, and hypotrichosis means a coat with less hair than normal [2]. In a small number of dogs and cats, the cause is inborn: the hair follicles did not form or work normally from the start [2][3].
These inborn forms are rare. Most hair loss in pets is acquired later in life, and only a few congenital forms are known, linked to faults in how the hair follicles develop [2]. Congenital means present from birth.
If your puppy or kitten has thin or missing hair, or your pet’s coat changes, see your vet. Most hair loss is acquired, not inborn [2][3], and other causes need different care.
For hair loss in general, see hair loss in dogs and hair loss in cats.
What it looks like
Some animals have a sparse coat or almost no hair from birth [4]. In others the coat starts out normal and changes in the first weeks, months or years of life [1]. Signs can include a dry, frizzy or dull coat, loss of the longer outer hairs, a change in coat color, or curly or twisted hairs [1]. In some forms the hair loss follows the coat color and only affects hair of one color [1].
The genes that shape hair follicles can also shape teeth. Hairless dog breeds often have missing or oddly shaped adult teeth along with their sparse coat [4].
Hairless breeds
- Dogs: the Chinese Crested, Peruvian and Mexican hairless breeds carry a change in a gene called FOXI3. One copy of the change gives the sparse or absent coat and the dental changes, a condition known as canine ectodermal dysplasia [4].
- Cats: the Sphynx is a hairless breed, and its coat type has been linked to changes in a hair keratin gene called KRT71 [5].
Inherited hair loss in other dogs
- Ectodermal dysplasia: some dogs born with hair loss have an ectodermal dysplasia tied to the ectodysplasin A gene [3]. This is an inborn defect of the skin, hair and related structures.
- Follicular dysplasia: a group of mostly breed-linked conditions in which the follicles form or regrow poorly. They usually begin in young dogs, and a genetic cause is suspected but not always proven [1][3].
- Black hair follicular dysplasia: in dogs with coats of two or three colors, only the black hair is lost [1]. The black hair can lose its shine from about 4 weeks of age, and those areas are bare or nearly bare by 6 to 9 months [1]. It has been reported in many breeds, among them Bearded Collies, Papillons and Large Munsterlanders, and in mixed breeds [1].
- Irish Water Spaniels: hair loss tends to start between 2 and 4 years of age at the back of the body and slowly spreads to the tail and trunk [1].
Two other inherited coat conditions in dogs have their own pages: color dilution alopecia in dogs and alopecia X and seasonal flank alopecia in dogs.
Inborn coat changes in other cats
- Devon Rex: this breed has a short, curly coat, and its curl is also linked to the KRT71 gene [5]. Rex coats tend to have few or no guard hairs, and the whiskers are often curly and break easily [5].
Skin problems that can follow
Dogs with follicular dysplasia are prone to skin infections around the hair follicles, and bare skin can burn in the sun [1]. Some develop scaly skin or blackheads in the bald areas [1].
How vets find the cause
A review on hair loss without inflammation in dogs explains that no single test gives the answer. The vet puts together the pet’s history, a full examination with blood tests, and skin samples taken from well-chosen spots [3]. For inborn forms, a microscope look at a skin sample (histopathology) is often what tells one type of follicle problem from another [2].
Care
There is no specific treatment that brings back the hair in these inherited conditions [1]. Care aims at the problems that follow: your vet will treat any skin infection, and may suggest ways to protect bare skin from the sun and manage scaling [1]. Because the cause is genetic, affected dogs should not be bred [1].
At home, as directed by a vet:
- do not put any cream, oil or product on the skin unless your vet tells you to;
- keep bare skin out of strong sun [1];
- watch for bumps, redness, crusts or sores on bare or thin-haired skin;
- go back for any recheck your vet suggests.
When to see your vet
See your vet if your dog or cat has:
- thin or missing hair from birth, or hair loss that develops later [1][4];
- missing or abnormal teeth along with a thin coat [4];
- bumps, scaling or signs of infection on thin-haired skin [1].
FAQ
Are hairless breeds unhealthy?
Hairless dog breeds often have missing or misshapen adult teeth [4], and bare skin is prone to sunburn and follicle infections [1]. Ask your vet how to care for your pet’s skin and teeth.
Can a puppy from a normal-coated breed have inherited hair loss?
Yes. Follicular dysplasias have been reported in many breeds and in mixed-breed dogs, and some start only after puppyhood [1].
Which cat breeds have inborn coat changes?
The Sphynx is bred to be hairless, and the Devon Rex has a curly coat; both coat types are linked to the KRT71 gene [5].
The bottom line
Hypotrichosis means less hair than normal. Some dogs and cats are born with it, and some hairless breeds, such as the Chinese Crested and the Sphynx, have been bred for it. Inborn coat defects in hairless dogs come with dental changes, and bare or thin-haired skin is prone to infection and sun damage. Most hair loss is acquired rather than inborn, so see your vet to find the cause.
This article is for general information only and does not replace advice from your veterinarian. If your pet has thin or missing hair, see your vet.
Sources
- Canine Follicular Dysplasias. Small and Large Animal Dermatology Handbook, Vol. 2, chapter 1.11. University of Minnesota Libraries Publishing, CC BY 4.0. https://open.lib.umn.edu/animaldermatology2/chapter/canine-follicular-dysplasias/
- Mecklenburg L. An overview on congenital alopecia in domestic animals. Vet Dermatol. 2006;17(6):393-410. https://pubmed.ncbi.nlm.nih.gov/17083571/
- Welle MM. Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid. Vet Pathol. 2023;60(6):748-769. https://pubmed.ncbi.nlm.nih.gov/37191329/
- Kupczik K, Cagan A, Brauer S, Fischer MS. The dental phenotype of hairless dogs with FOXI3 haploinsufficiency. Sci Rep. 2017;7:5459. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC5511229/
- Zorc M, Horvat T, Tanšek A, Ferme T, Dovč P. Selection Signatures Reveal Candidate Genes for the Cornish Rex Breed-Specific Phenotype. Genes (Basel). 2024;15(3):368. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC10969784/