Sex hormones can affect a dog’s skin and coat. A veterinary dermatology handbook from the University of Minnesota groups these problems as sex hormone dermatoses [1]. Most involve too much estrogen, a female sex hormone; too much testosterone is less common, and too much progesterone is rare [1]. Vets usually think of them in a dog that has not been spayed or neutered and has hair loss without inflammation, once thyroid and adrenal disease have been ruled out [1].
Have your vet check any hair loss, rash or itch that keeps going or spreads.
For other causes of hair loss, see hair loss in dogs.
Male dogs with testicular tumors
In unneutered males, extra estrogen most often comes from a hormone-making testicular tumor, called a Sertoli cell tumor [1]. The handbook calls the result male feminization syndrome. Hair thins evenly on both sides of the body, starting around the tail and back legs and moving onto the belly, chest, neck and flanks, while the head and lower legs are spared [1]. The skin may darken. Itch is usually absent unless a skin infection sets in [1].
Other signs can include a hanging sheath, enlarged nipples and breast tissue, and a lump in one testicle while the other one shrinks [1]. Testicles that never came down into the scrotum are much more likely to develop these tumors [1]. Middle-aged and older dogs are affected most [1].
Unspayed female dogs with hormone imbalances
In unspayed females, extra estrogen can come from cysts or tumors of the ovaries, mostly in middle-aged and older dogs [1]. The pattern of hair loss is similar: even on both sides, starting at the groin, flanks and the area under the tail, often with darker skin [1]. Itch is not usual unless greasy skin or a skin infection develops [1].
The handbook also lists irregular or long heat cycles (estrous cycles), an enlarged vulva and nipples, and blackheads on the belly [1].
Estrogen cream used by a person
A dog can also take in estrogen from a person’s skin. In one report, six dogs from three homes lost hair after close contact with owners who used hormone creams or gels on their own skin [2]. Several of the dogs also showed feminizing changes [2]. In a second report, five dogs lost hair after contact with an estrogen gel their owners used for menopause symptoms, and the dogs’ blood tests did not always show high estrogen [3].
Tell your vet about any hormone creams, gels or sprays used in your home. Our guide to hormone gels and sprays for people explains how pets are exposed.
How vets diagnose them
Your vet will ask about your dog’s history, whether your dog is spayed or neutered, and any hormone products used in the home. The handbook explains that blood hormone tests may not settle the question, because standard tests measure only one hormone and levels change through the day [1]. Your vet may first rule out other hormone diseases, feel for testicle or belly lumps, and may suggest imaging [1]. For another hormone-related coat problem, see Alopecia X and seasonal flank alopecia in dogs.
Treatment
Your vet will advise on treatment for your dog, based on the cause your vet finds. For the tumor and ovary forms, the handbook describes surgery to remove the source of the hormone [1]. When a person’s hormone product is the cause, the dogs in both reports regrew hair once contact stopped or was reduced [2][3].
At home, as directed by a vet:
- tell your vet about any medicines or hormone products used by people your dog is in close contact with;
- note where the hair loss or rash started and how it spreads, so you can show your vet;
- go back for every recheck.
Outlook
The handbook reports that most dogs improve once the hormone source is removed, though it can take months, and signs can come back if a tumor has spread [1]. Rarely, high estrogen damages the bone marrow, which is serious [1].
These are statements about groups of dogs. They cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- hair loss on both sides of the body [1];
- hair loss with itching or a skin rash [1];
- in an unneutered male, a swollen or uneven testicle, a hanging sheath or enlarged nipples [1];
- in an unspayed female, a swollen vulva or nipples, or unusual heat cycles [1];
- any skin change that keeps going or grows.
The bottom line
Sex hormone problems can cause hair loss and skin changes in dogs. They are linked to testicular tumors in males, ovary problems in unspayed females, and hormone creams or gels used by a person in close contact with the dog. Only a vet can find the cause, and your vet will advise on treatment.
This article is for general information only and does not replace advice from your veterinarian. If your dog has hair loss or a rash that does not go away, see your vet.
Sources
- Torres SMF. 1.7 Sex Hormone Dermatoses, Canine. In: Small and Large Animal Dermatology Handbook, Vol. 2. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology2/chapter/sex-hormone-dermatoses-canine/
- Berger DJ, Lewis TP, Schick AE, Miller RI, Loeffler DG. Canine alopecia secondary to human topical hormone replacement therapy in six dogs. J Am Anim Hosp Assoc. 2015;51(2):136-42 (abstract, PubMed 25695561). https://pubmed.ncbi.nlm.nih.gov/25695561/
- Wiener DJ, Rüfenacht S, Koch HJ, Mauldin EA, Mayer U, Welle MM. Estradiol-induced alopecia in five dogs after contact with a transdermal gel used for the treatment of postmenopausal symptoms in women. Vet Dermatol. 2015;26(5):393-6 (abstract, PubMed 26216160). https://pubmed.ncbi.nlm.nih.gov/26216160/