What this means
A crust is dried fluid, blood or pus on the skin's surface, and a sore is a spot where the skin has lost its top layer. Sometimes both are seen together: a sore with a crust over it. It is important to note where they are, because certain places point towards different causes.
Crusts or sores on the nose and muzzle, around the eyes, on the ear tips or on the lips are sometimes linked to immune system disorders. Crusts over the bony points of the legs, over joints or on the ear tips may be linked to friction or to inherited skin diseases. Round, crusted patches that spread outwards from the centre look more like a skin infection.
Note what the lesions themselves look like: whether they are moist, dry, discharging pus or bleeding, whether they are painful, and whether your dog scratches at them. Also notice whether they are spreading, whether they come back in the same place and whether they simply disappear when washed. A photo every few days helps your vet see how things are progressing.
Do not try to pick off the crusts or clear them yourself. That can damage the skin and open the sore again. Write down when the lesions appeared and show them to your vet.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Skin infection
Bacteria, yeast or fungus can cause round crusted patches, pustules and ulcerated skin. The lesions often spread and may smell.
About the condition: Skin infections -
Immune system disorders
When the immune system attacks the dog's own skin, sores and crusts appear, often on the nose, muzzle, around the eyes and on the ears. The lesions can be painful.
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Dermatomyositis
This is an inflammatory disease that can affect the skin and muscles. Crusts and sores appear on the muzzle, ear tips and bony points of the legs.
About the condition: Dermatomyositis -
Inherited skin disease
In some dogs the skin is fragile from birth and is easily damaged, so crusts form where it rubs or is pressed. A vet needs to assess this.
About the condition: Dystrophic epidermolysis bullosa -
Skin and eye inflammatory syndrome
A rare disorder in which inflammation affects both the skin and the eyes. The skin ulcerates and crusts, and the nose and lips lose their colour.
About the condition: Uveodermatologic syndrome -
Other skin diseases
Many skin diseases produce crusted areas or bumps. What the disease is will be decided by a vet after examining the dog and taking a skin sample.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Where the lesions are: nose, muzzle, ears, joints, bony points of the legs
- Whether they are moist, dry, discharging or bleeding
- Whether they are painful and whether your dog scratches at them
- Whether they are spreading or returning in the same place
- Whether the eyes or the colour of the nose or lips have changed
- Whether your dog's energy, walking and eating are as usual
When to book a routine visit
Book a visit if crusts or sores do not clear within a few days, keep returning, spread or are painful, especially if they have appeared on the nose, muzzle, ears or joints.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Autoimmune disorders Blood and immunity This is an umbrella term for conditions in which the immune system, instead of defending the body against germs, starts attacking the dog's own tissues. The skin, blood cells, joints or internal organs can be affected, so these diseases can look very different from one another. What the condition is and what caused it is for the vet to determine.
- Dermatomyositis Skin and coat Dermatomyositis is an inherited inflammatory disease that affects the skin and sometimes the muscles. Its signs can appear at a young age, and it can range from barely noticeable skin changes to muscle wasting that makes eating and swallowing difficult. Damaged skin can leave lasting scars and bald patches.
- Dystrophic epidermolysis bullosa Skin and coat Dystrophic epidermolysis bullosa is an inherited skin disease in which a protein that anchors the outer layer of skin to the layers beneath is missing. The skin becomes very fragile: ordinary rubbing or a minor knock leaves blisters and sores that are slow to heal. It shows up in puppies, and the diagnosis is made by a vet.
- Skin problems Skin and coat This is an umbrella term for a range of skin disorders, from allergies and parasites to infections, hormonal diseases or growths in the skin. The skin also reflects a dog's overall health, so changes in it sometimes point to a problem elsewhere in the body, and constant itching or soreness takes a real toll on a dog's comfort. What lies behind particular changes is for a vet to work out.
- Skin infections Skin and coat Skin infections are caused by bacteria or yeast that start to multiply when the skin's defences are weakened, for example by an allergy, parasites, moisture trapped in skin folds or constant scratching. An infection can stay on the surface or reach the deeper layers of the skin, causing pain and intense itching. What caused the infection and what keeps it going is for a vet to work out.
- Uveodermatologic syndrome Blood and immunity Uveodermatologic syndrome is an immune disease in which the body's immune system attacks the pigment-producing cells in the eyes, the skin and the coat. In the eyes it causes deep inflammation that can damage vision and lead to blindness, while the skin and coat lose their colour in places. The eye changes are urgent, so if an eye turns red or painful or vision drops, the dog needs a vet immediately.
- Ear mites Parasites Ear mites are microscopic parasites that live in the ear canal and feed on ear wax and the surface of the skin. They cause intense itching and a dark, dry discharge. The mites pass easily between animals, especially from cats and among puppies; whether they are behind an itchy ear is for a vet to establish by examining the discharge.
Body systems: Blood and immunity Skin and coat Parasites