Petco Text Logo
Petco Pet Logo

My dog has fur loss in strips, black skin. What could be causing it?

Updated On September 23rd, 2025

Pet's info: Dog | Bullmastiff | Female | unspayed | 1 year and 7 months old | 90 lbs

My bull mastiff is losing her fur. Almost seems in strips. Down to the blacl skin. Started about 2 months ago. She is about 18 months old and has regular vet checkups. They cant seem to find out what is wrong with her.

4 Answers

Most Helpful Answer

Image profile

Answered By Shaneez Wallani, DVM

Veterinarian

Published on March 25th, 2019

Hair loss can be caused by bacterial infection, parasitic infection (like mites or fleas) or fungal infection (like ringworm), dietary or environmental allergies or sensitivities, immune system disorders, or a combination of the above. I recommend making an appointment to have Sandy seen by your veterinarian again to help determine the cause of the hair loss as soon as you can. The vet may want to look at a sample from the area (taken by a procedure known as a skin scraping) and examined under the microscope to determine what kind(s) of infection may be present and to figure out what medication is appropriate for treatment. If these tests have been done and the results did not help provide a diagnosis, I recommend asking your vet for a referral to a dermatologist for further workup. Having Sandy spayed may also help her skin, as some skin conditions can be worsened by hormone fluctuations that occur in unspayed female dogs.

Vote icon

1Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Image profile

    Answered By Dr. Elizabeth

    Veterinarian

    Published on July 6th, 2017

    The most common reason for redness and hair loss in the lower back area is fleas. Put Nik on a flea prevention. If you can find an oral product, these typically work best. Environmental allergies or food allergies can also cause skin issues but rule out parasites first. The darker colored skin is in response to the inflammation in her skin. Typically a steroid or antihistamine can help decrease the inflammation. Talk to her veterinarian about what is the next most appropriate step.

    Vote icon

    1Pet Parents found this answer helpful

  • Image profile

    Answered By Dr. Leigh, DVM

    Veterinarian

    Published on December 13th, 2016

    She could have a skin infection, allergies, mites, flea allergy dermatitis, etc. Your vet can do a skin scrape, cytology, and/or culture to help diagnose and then prescribe medications to treat. She may need an antibiotic, antihistamine, corticosteroid, or other medications depending on the diagnosis.

    Vote icon

    1Pet Parents found this answer helpful

  • Image profile

    Answered By Dr. Strydom, DVM

    Veterinarian

    Published on April 11th, 2019

    This actually looks very much like a flea allergy dermatitis to me. Of course it is impossible for me to diagnose via the internet with one photo. I am all for owners trying things at home for their pet before going to the vet as long as the animal is doing otherwise well. If those home treatments are not working, then I suggest you get Riley to your vet for an exam so you can figure out what is going on and get him the appropriate treatment. Best wishes.

    Vote icon

    1Pet Parents found this answer helpful

See More Answers

Related Questions

Petco Pet Education Center
Health & Wellbeing
Hair loss in armpit and belly/genital area. Skin black and leathery looking. Skin inside ears also black and leathery looking with some edema.
Skin problems can have a variety of causes, sometimes more than one. Allergies, bacterial or fungal infections, even contact with some surfaces or substances will cause itching and/or hair loss. It is important to have the problem checked by your vet to determine if there is a medical cause for your pet’s skin issues and treat accordingly. In pets of all ages, fleas, food allergies and exposure to chemical irritants such as cleaners and soaps can be a cause. Any one of these may not be enough to trigger the breakouts, depending on how sensitive your pet is, but a combination can be enough to start the itch-scratch cycle. Finding out the cause and eliminating it is the best course of action. With flea allergies, if your pet is sensitive enough, a single bite can cause them to break out scratch enough to tear their skin. Check for fleas with a flea comb. Look for fleas and/or tiny black granules, like coarse black pepper. This is flea feces, consisting of digested, dried blood. You ma
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
We adopted our pet, who is 1.5-2.5 years old, and suffered from a skin condition (balding). Her hair has gotten worse over the last six months. Shes losing her good hair now too, and shedding excessively. She also has gotten black dots on her skin th
Poor Sisi! I'm sorry to hear that she's having this problem. The most common conditions we see in dogs that cause hair loss and scaling would include allergies, bacterial or fungal skin infections, or skin mites (mange). If she has been treated for these conditions and has not improved, then I would agree that it sounds like something else may be wrong. Less common causes of these symptoms could include a systemic illness like Cushing's diseases or hypothyroidism (not very common in young dogs, but possible), or an autoimmune disease such as lupus or pemphigus foliaceus. I'm not sure what specific blood work has been done on Sisi, but you could certainly talk to your veterinarian about whether testing for these illnesses has been done. If lab work shows no abnormalities, then a skin biopsy would likely be the next recommended step to try and get a diagnosis.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My dog has been losing his hair on both his back hind legs as well as his sides and it is a black/purple color.What is this?He is not in pain.
Skin problems can have a variety of causes, sometimes more than one. It is important to have the problem checked by your vet to determine if there is a medical cause for your pet’s skin issues and treat accordingly. In pets of all ages, fleas, food allergies and exposure to chemical irritants such as cleaners and soaps can be a cause. Any one of these may not be enough to trigger the breakouts, depending on how sensitive your pet is, but a combination can be enough to start the itch-scratch cycle. Finding out the cause and eliminating it is the best course of action. With flea allergies, if your pet is sensitive enough, a single bite can cause them to break out scratch enough to tear their skin. Check for fleas with a flea comb. Look for fleas and/or tiny black granules, like coarse black pepper. This is flea feces, consisting of digested, dried blood. You may find tiny white particles, like salt, which are the flea eggs. Applying a good topical monthly flea treatment and aggressivel
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Hello, I have a Wire Hair Fox Terrier who has awful allergies. Her skin seems to have a black coating, for lack of a better word, on several spots of her body. Is this common for types of fleas, mites or skin infections?
She could have a skin infection, mites, fleas, ringworm, allergic dermatitis, etc. Your vet can do a skin scrape, cytology, or culture to help diagnose and then prescribe medications to treat the problem. She may need an antibiotic, anti-histamine, corticosteroid, or other medications depending on the cause. Make sure to treat her with a monthly flea medication like NexGard, Frontline, Advantage, or Revolution to prevent fleas.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My dogs skin is peeling and i think its getting itchy. Im scared because his skin is peeling his hair too.
Skin problems can have a variety of causes, sometimes more than one. Allergies, parasites, bacterial or fungal infections, even contact with some surfaces or substances will cause itching, rash and/or hair loss. It is important to have the problem checked by your vet to determine if there is a medical cause for your pet’s skin issues and treat accordingly. In pets of all ages, fleas, food allergies and exposure to chemical irritants such as cleaners and soaps can be a cause. Any one of these may not be enough to trigger the breakouts, depending on how sensitive your pet is, but a combination can be enough to start the itch-scratch cycle. Finding out the cause and eliminating it is the best course of action. With flea allergies, if your pet is sensitive enough, a single bite can cause them to break out scratch enough to tear their skin. Check for fleas with a flea comb. Look for fleas and/or tiny black granules, like coarse black pepper. This is flea feces, consisting of digested, dr
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My French mastiff is 9 months old losing massive amounts of hair. He is bald in spots now what can I do what is it? Please suggest medicine or food diet for him
Causes of hair loss could include external parasites such as fleas and mange mites, and allergies (we can have allergies to food or things in the environment such as pollen/grass/dust) and sometimes infections of the skin with bacteria or yeast. I would recommend a visit with your vet to have a skin scrape done to be sure we don't have mange mites present that need treatment. I would start a flea preventative such as Advantage (available over the counter) or your vet also has prescription medication for this issue. You can also refer to this article for ideas on how to manage him until your vet is able to examine him: https://www.petcoach.co/article/5-things-you-can-do-at-home-to-keep-your-dog-s-allergies-at-bay-t/
Updated on September 24th, 2025
Petco Pet Education Center
Training & Behavior
Hello i have a femal pitbull and shes about 6 1/2 years old and she has baldness from her ankles to her knees shes bites and licks all the time now look to be red sores . Ive taken her to vet they did nothing for her . Please tell me what this is and
Hair loss can be caused by bacterial infection, parasitic infection (like mites or fleas) or fungal infection (like ringworm), dietary or environmental allergies or sensitivities, immune system disorders, or a combination of the above.Based on the pictures and the description of how itchy she is, I'm concerned that Nhala may have mange. I recommend making an appointment to have Nhala seen by your veterinarian again to help determine the cause of the hair loss as soon as you can. The vet may want to look at a sample from the area (taken by a procedure known as a skin scraping) and examined under the microscope to determine what kind(s) of infection may be present and to figure out what medication is appropriate for treatment. If these tests have been done and the results did not help provide a diagnosis, I recommend asking your vet for a referral to a dermatologist for further workup. Spaying Nhala may also help, as some skin conditions are exacerbated by the hormone fluctuations of t
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I have a Doberman female. She lives in country and came home from my moms. She started losing hair on her armpits and around the inside of her back legs. It's red, irritated, she has puss filled lumps, and black specs all around where she lost hair.
She could have a skin infection, allergies, mites, flea allergy dermatitis, etc. Your vet can do a skin scrape, cytology, and/or culture to help diagnose and then prescribe medications to treat. She may need an antibiotic, antihistamine, corticosteroid, or other medications depending on the diagnosis.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
i have a 13 yo male Cairn Terrier that is starting to lose his hair one the left side. What is going on? I buy him healthy no gran dog food, he walks 3 to 4 x's a day and is very well taken care of.
Hair loss can have a variety of causes. One of the first things to determine is whether he is scratching himself in that area or not. Dogs often scratch themselves at night when we are sleeping so it is harder to see. If he is scratching, the hair loss could be due to parasites such as fleas or mites, a bacterial infection, yeast overgrowth, or skin allergies. If he does not seem to be itchy, hair loss can be caused by hormonal changes or certain endocrine diseases. These are just some of the possibilities. In order to determine what is most likely, I recommend taking him to your local veterinarian for a thorough exam and an initial skin test if needed to determine the cause.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Yes my dogs skin is turning black and her hair is falling out I'm wondering what could it be
It may be due to true skin problems like allergy or skin infection. However, if she doesn't show excessive skin itchiness or redness she may have hormonal problems (diabetes, underactive thyroid gland, overactive adrenal gland etc). You shoud get her checked by your vets. They are likely to recommend skin testing and blood test to find out what is going on.
Updated on September 24th, 2025
image
Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Book Now

Sponsored