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Dog laying in grass with a ball

Skin Infections in Dogs

Skin infections are frequently seen by the veterinary surgeon. Skin disease can look very similar whatever the cause, with itchiness (pruritus) often occurring. Bacterial skin infections are common and may need many weeks of antibiotic treatment.

The skin forms the outer covering of the body and protects against a hostile external environment. This includes heat/cold, water/dryness, chemical toxins, mechanical damage, sunlight and a host of would-be invaders such as bacteria, fungi, yeasts, mites, insects and viruses.

Bacterial skin infection (pyoderma):
Bacterial infections often result when some skin diseases have not been successfully controlled. There are a number of bacteria living on the skin normally. These bacteria can cause a secondary bacterial infection if there is a break or defect in the skin. A bacterial skin infection is also known as a pyoderma.

Pyoderma may be localised (small areas) or more generalised (larger areas).The superficial layers of skin are the most commonly affected. However, sometimes the deep layers of skin become involved, trapping infection and possibly causing scarring.

Underlying causes:
The most common skin diseases where a secondary pyoderma can occur are:

  • Allergies (inhaled, dietary, contact and flea-bite allergies).
  • Ectoparasite infestations such as fleas, lice and mites.
  • Hormone disorders, such as hypothyroidism or Cushing's disease.
  • Surface layer skin defects (greasy skin).
  • Deep skin folds with irritation. 

Sudden onset bacterial infections:
There are two conditions that occur much more rapidly.

(1) Abscess:
This is a bacterial infection of the deep skin layers and underlying tissues, usually associated with a bite from another animal (puncture wound), an infected wound, or embedded material such as a grass seed (foreign body) Pus is usually a feature.

(2) Moist eczema:
This is a pyoderma of the superficial layers of the skin, and commonly occurs quickly, especially on a hot humid day. An irritation such as an insect bite is often the initial cause, but the animal’s biting or scratching creates a large raw moist weeping infected sore.

  • Non-bacterial skin infections:
    Ringworm, a fungal infection of the hair and surface skin (less common)
  • Malassezia, a yeast infection of the skin surface which can also be common in allergic skin disease and which often occurs alongside pyoderma. It often has a distinctive odour.
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  • Symptoms of pyoderma:

    Symptoms will vary from animal to animal, and may include:

    • Itchiness (pruritus).
    • Hair loss (alopecia) and poor hair coat.
    • Small, red, raised spots on the skin (papules).
    • Small discharging areas of pus, often in a hair follicle (pustules).
    • Scabs/crusts.
    • Inflammation (pain, heat, redness, and swelling).
    • Bad odour,
    • Pus (thick yellow/red/green discharge) especially with deep infections.

    Symptoms of sudden-onset bacterial infections:

    • Abscess: A localised area that will be painful, red, hot and swollen. An entry wound may be visible. Pus may discharge from it.
    • Moist Eczema: a so-called ‘hot spot’, because the superficial skin layer is hot, with a circular area of hair loss. It is painful and the infected area is often covered in sticky crusts, pus and matted hair.

    Symptoms of non-bacterial infections:

    • Ringworm will give patches of broken hairs, hair loss, and greyish crusts.
    • Malassezia leads to thick greasy coat, with a characteristic ‘wet dog’ smell. This is often seen in association with a pyoderma.

  • Diagnosis of a bacterial infection can usually be made by your veterinary surgeon after examining the characteristic changes in the skin and taking samples for microscopic examination to find the type of organism involved. Cultures from samples of pus can identify the bacteria involved and help to choose the best antibiotic for treatment. 

    However, it is also very important to identify the underlying cause of a pyoderma and this can be very challenging. It is necessary to do this to manage the skin disease in the long-term. If only the pyoderma is treated it may resolve, but then come back again. A wide variety of tests may be necessary, often conducted over a prolonged period of time. These may include

    • A skin scraping, including the deeper skin layers (to look at under the microscope for bacteria, parasites, fungi and yeasts, and also to culture).
    • A special exclusion diet trial.
    • Skin sensitivity tests
    • A variety of blood tests.

    Sudden-onset bacterial infections:
    An abscess or moist eczema is readily diagnosed by your veterinary surgeon from the symptoms.

  • Treatment may include some of the following:

    • Specific treatment of the primary or underlying skin disease
    • Treatment of the secondary bacterial infection. Many weeks of antibiotic treatment may be necessary for long-standing or deep infections. It is very important that antibiotics are given everyday at the correct time and that no doses are missed. A common reason for treatment failure is the owner not completing the full course of antibiotics. The course should be completed even if the dog’s skin already looks a lot better. Alternative longer acting treatments are available and your veterinary surgeon will decide upon the best treatment regime.
    • Corticosteroid or antihistamine medication may be prescribed to reduce the inflammation and pruritus.
    • Support of damaged skin/hair. Various shampoos and diets can help to promote a healthy skin and coat.
    • Drainage of an abscess together with antibiotic treatment.
    • Specific treatment for any fungal skin infections.
    • Treatments for skin parasites will also be necessary if parasites have been identified.
    • Other specific treatments (eg immuno modulation or immuno therapy)

    Your veterinary surgeon will select the treatment appropriate to each individual case. Long-standing cases will need treatment for many weeks, so it is important not to cut short any period of treatment that your veterinary surgeon prescribes.

  • Early diagnosis with appropriate treatment is essential.

    Regular flea treatment with an antiparasiticide for all animals in the household will protect against a common cause of skin disease that leads to secondary pyoderma.