Curly coat is caused by a mutation in the KRT71 gene that makes a dog’s hair curl if it gets long enough. Curly coated dogs can be bearded or smooth-faced and they can have a soft or wiry coat texture.
Our dog’s hair is composed of different types of keratin. A normal round hair shaft causes straight hair while a flattened hair shaft results in a bent and curly shape.
Dogs can have a wavy coat, big loose curls or small ringlets. If a dog has a more wavy than curly coat seems to depend on many factors, e.g. how many copies of the causal allele he has and of the overall hair texture, thickness or length.
The overall looks of a dog with wavy or curly hair depend on his hair length and the presence of furnishings. Shorthaired and non-bearded dogs for example can have the gene variant for a curly coat but their hair is simply too short to actually curl.
And some wirehaired dogs can have wavy or even somewhat frizzy hair even without having one of the mutations associated with a curly coat in dogs!
Curly coat is caused by different mutations in the KRT71 gene (keratin 71) on dog chromosome 27[1,4].
KRT71 is a keratin expressed in the inner root sheath of the hair follicle and plays a role in the correct growth of the hair follicle.
The mutant variant of KRT17 causing curly coat seems to significantly affect the structure of the keratin 71. This changes the shape of the hair shaft and causes a wavy or curly coat.
The common variant of KRT17 found in most of all curly dog breeds is Cu1. Another variant called Cu2 was found in Curly Coated Retrievers which are all fixed for a Cu2/Cu2 genotype[2,3].
The Cu2 allele also occurs in some other breeds like Lagotto Romagnolo, Bichon Frisé, Irish Terrier, Chesapeake Bay Retriever, Mudi, Spanish Water Dog, Kuvasz or Poodle. Please note that not all companies test for both variants!
All combinations of mutant alleles (Cu1/Cu1, Cu1/Cu2, Cu2/Cu2) cause a curly coat. And there even seem to be some dogs that have recombined haplotype with the Cu1 and Cu2 mutation on the same chromosome.
But there’s a downside… There is some evidence that the Cu2 allele might be a genetic risk factor predisposing affected for some forms of follicular dysplasia.
Curly hair due to Cu2 seems not to be anchored as tightly in the skin as curls caused by c1. Some owners of dogs with Cu2/- report that hair shafts on their dogs break more easily when exposed to mechanical friction, can be plucked quite easily or that their dogs suffer from symmetrical hair loss.
Aside from Cu1 and Cu2 there might be additional alleles at the Curly-Locus since there are still obviously curly dogs out there that don’t test positive for either of the known mutations.
Curly coat is an incomplete dominant trait, a dog only needs one copy of Cu1 or Cu2 to grow curly hair.
The effect of the curly alleles seems to be strongest in homozygous dogs (Cu1/Cu1, Cu1/Cu2, Cu2/Cu2) while heterozygous dogs (Cu1/cu, Cu2/cu) might only express wavy or looser and only moderately curly coat. Dogs with two wild-type alleles (cu/cu) will have a straight coat.
Curly Coat Calculator
Dogs with a curly coat can be carriers for the wild-type allele (Cu1/cu or Cu2/cu). Mating two carriers can produce puppies with a straight coat (cu/cu).
This simple tool can help you predict the outcome of different combinations of dogs with or without curly coat:
Curly Coat Types
Curly hair growth is only visible on dogs above a certain hair length.
Short Curly Coat
The Cu1 variant of KRT71 occurs in some shorthaired dog breeds.
But the hairs on a smooth-coated dog simply are most often too short to coil. But longer hairs along the back or the shoulders might show a suspiciously wavy growth pattern.
The Cu1 allele occurs (often at a very low frequency) in surprisingly many shorthaired dogs like Chesapeake Bay Retriever, German Shepherd Dog, Pharaoh Hound, Anatolian Shepherd Dog, Beagle, Australian Cattle Dog, Kelpie, Manchester Terrier, Pointer, Basset, Malinois, Bloodhound, Boxer, Great Dane, Whippet, Smooth Fox Terrier and many more.
The only exemption to this rule is found in shorthaired dogs with a bearded growth pattern since furnishings alone can make the hair on a genetically smooth-coated dog just long enough to curl. But we’ll get to that.
Long Curly Coat
On a longhaired dog without furnishings, only the areas with longer hairs will be curly. These dogs still have very short hair on face and legs which will not be curly.
Some breeds with this phenotype are Irish Water Spaniel, Epagneul de Pont Audemer, Wetterhoun, Mudi, Croatian Sheepdog, Kuvasz or the Curly Coated Retriever.
Curly Coated Retrievers have a very tight and crisp curl phenotype. This breed is fixed for Cu2/Cu2 which might make them vulnerable to coat disorders or give them their sparsely haired “rat tail”.
A curly or wavy coat also occurs in some Borzoi, Border Collies, Chihuahua, Yorkshire Terrier, Leonberger, Westie, Tibetan Terriers and other dog breeds with (sometimes) longhaired phenotypes although not all of them consider curly a standard coat type.
Wire Curly Coat
Shorthaired dogs with furnishings will have long hairs on their face, eyebrows and legs. The wiry body hair has a moderate and even length and will in most cases be long enough to express a curly phenotype.
Some examples for curly wirehaired dogs are Airedale Terrier, Fox Terrier, Lakeland Terrier, Welsh Terrier and very few Irish Terrier.
Bearded Curly Coat
Dogs that express a combination of long hair, curly hair and furnishings will have an ever-growing and non-shedding coat.
This is the coat type typical for Poodles, Bichon Frisé, Pumi, Barbet, Bolognese, Lagotto Romagnolo or Spanish Water Dog and many Irish Soft Coated Wheaten Terrier.
Curly Dog Breeds
Here are some of the dog breeds where curly coats are common:
- Airedale Terrier
- American Water Spaniel
- Bedlington Terrier
- Bergamasco Sheepdog
- Bichon Frise
- Bolonka Zwetna
- Chesapeake Bay Retriever
- Croatian Sheepdog
- Curly Coated Retriever
- Epagneul de Pont Audemer
- Irish Water Spaniel
- Kerry Blue Terrier
- Lagotto Romagnolo
- Lakeland Terrier
- Portuguese Water Dog
- Soft Coated Wheaten Terrier
- Spanish Water Dog
- Welsh Terrier
- Wire Fox Terrier
 Cadieu et. al.. Coat variation in the domestic dog is governed by variants in three genes. Science 326:150-3, 2009. Pubmed reference: 19713490. https://doi.org/10.1126/science.1177808
 Bauer A, Hadji Rasouliha S, Brunner MT, Jagannathan V, Bucher I, Bannoehr J, Varjonen K, Bond R, Bergvall K, Welle MM, Roosje P, Leeb T. A second KRT71 allele in curly coated dogs. Anim Genet. 2019 Feb;50(1):97-100. doi: 10.1111/age.12743. Epub 2018 Nov 15. Erratum in: Anim Genet. 2021. https://doi.org/10.1111/age.12743
 Salmela, E., Niskanen, J., Arumilli, M., Donner, J., Lohi, H., Hytönen, M.K., Salmela, E., Niskanen, J., Arumilli, M., Donner, J., Lohi, H., Hytönen, M.K., Salmela, E., Niskanen, J., Arumilli, M., Donner, J., Lohi, H., Hytönen, M.K. : A novel KRT71 variant in curly-coated dogs. Anim Genet 50:101-104, 2019. https://doi.org/10.1111/age.12746
 Online Mendelian Inheritance in Animals (OMIA). Sydney School of Veterinary Science, University of Sydney. OMIA 000245-9615 (08/2021): Curly coat in Canis lupus familiaris. https://www.omia.org/OMIA000245/9615/
 Paw Print Genetics: Cu Locus (Curly Hair).
 Dreger DL, Hooser BN, Hughes AM, Ganesan B, Donner J, Anderson H, et al. (2019). True Colors: Commercially-acquired morphological genotypes reveal hidden allele variation among dog breeds, informing both trait ancestry and breed potential. PLoS ONE 14(10): e0223995. https://doi.org/10.1371/journal.pone.0223995