Fungal infection - fungal or yeast skin infection in dogs

Fungal infections in dogs are infections of the skin, coat or nails caused by fungi or yeasts. The two most common forms are dermatophytosis, commonly known as "ringworm", and an overgrowth of the yeast Malassezia. Below you can read what both forms involve, how contagious they are, and what to watch for.

A quick note first

A quick note first: Fidello is not a veterinarian. This page is intended to inform you and does not help you make a diagnosis. If you have doubts about your dog's health, or recognize the signs described below, always contact a veterinarian.

What is a fungal infection in dogs?

In practice, "fungal infection" in dogs covers two quite different conditions that are often used interchangeably but are not the same.

Dermatophytosis is caused by fungi that break down keratin, the protein that makes up hair, skin and nails. These fungi live on the skin and in the hair shaft and are transmitted through direct contact with an infected animal, or via spores on objects such as brushes, baskets or bedding.

Malassezia dermatitis is caused by a yeast that is naturally present in small amounts on the skin of every dog. Problems only arise once this yeast multiplies uncontrollably, usually because the skin barrier has been disrupted by, for example, an allergy, a hormonal disorder, or excess moisture in skin folds.

Which dogs are at risk?

With dermatophytosis, young dogs, older dogs and dogs with a weakened immune system are at increased risk, because their immune defences suppress the fungus less quickly (source status: confirmed, recognized veterinary reference standard). Dogs with a dense, long coat that are often in damp or dirty environments are also more likely to become infected.

With Malassezia dermatitis, certain breeds are more frequently mentioned in connection with the condition, including the Basset Hound, the Cocker Spaniel, the West Highland White Terrier, the Shar-Pei and other breeds with skin folds or wide, drooping ears (source status: confirmed, recognized veterinary reference standard). This is because skin folds and closed ear canals create a warm, moist environment in which the yeast multiplies more easily. This list is not exhaustive: both conditions can occur in any breed.

Symptoms

The signs differ depending on the type of fungal infection:

• with dermatophytosis: round, bald or thinning patches, sometimes with a scaly or crusty edge, often on the head, ears or legs, which can gradually grow larger;
• with dermatophytosis: broken hairs around the patch, and sometimes mild itching, although many dogs show no itching at all;
• with Malassezia dermatitis: itching, redness and greasy, sometimes flaky skin, particularly in skin folds, between the toes, in the armpits or groin;
• with Malassezia dermatitis: a noticeably musty or yeasty smell from the skin or ears;
• with both forms: chronically recurring symptoms when the underlying cause is not addressed.

Because these signs can also occur with other skin conditions, such as allergies or parasitic infections, appearance alone is not enough to determine exactly which condition is present.

When to see a veterinarian

Contact your veterinarian if you notice bald or scaly patches, persistent itching, redness or an unpleasant smell on your dog, especially if the symptoms persist, spread or keep coming back. If dermatophytosis is suspected, acting quickly is particularly important: the fungus is contagious to other pets and can also spread to people (zoonotic), especially children, the elderly and people with a weakened immune system. Malassezia dermatitis is not contagious to people or other animals, but it often points to an underlying problem that a veterinarian should assess.

How is it diagnosed?

A veterinarian makes the diagnosis using targeted tests rather than by appearance alone. If dermatophytosis is suspected, a fungal culture, a PCR test, or examination of hairs and skin scrapings under a microscope may be used; a Wood's lamp can be supportive, but not every fungal species fluoresces under it, so a negative result does not rule out an infection. If Malassezia dermatitis is suspected, skin cytology is usually used: an impression smear or tape strip of the skin examined under a microscope for the presence of yeast cells. This testing is intended for the veterinarian to determine the correct diagnosis and approach, not something you can assess yourself as an owner.

Treatment in outline

A treatment plan is always determined by the veterinarian and depends on the type of fungal infection, the extent of the symptoms, and any underlying cause. For dermatophytosis, a veterinarian may choose a topical treatment with a medicated shampoo or cream, an oral treatment, or a combination of both, depending on severity and spread. For Malassezia dermatitis, treatment usually focuses on controlling the yeast with a specific shampoo, lotion or medication, and especially on identifying and addressing the underlying cause, such as an allergy or hormonal disorder, since otherwise the yeast overgrowth tends to keep returning. Which approach, which product and what dosage is appropriate is determined by the veterinarian for each dog individually; there is no treatment that guarantees the same result for every dog in every situation.

What you can do yourself

In addition to the treatment prescribed by the veterinarian, you can contribute in practical, non-medical ways as an owner:

• if dermatophytosis is suspected: temporarily limit contact with other pets and with children until your veterinarian advises otherwise, and wash your hands after touching your dog;
• keep your dog's bedding, brushes and baskets separate and clean them regularly in a way recommended by your veterinarian;
• keep skin folds, ears and the area between the toes well dried after bathing or walking in wet weather, especially for breeds prone to this;
• only use shampoo or skin care products recommended by your veterinarian, and do not switch products on your own initiative;
• complete a prescribed treatment in full, even if the skin already looks better, to prevent the infection from returning.

These measures support your dog's wellbeing but do not replace veterinary treatment.

Prevention

Dermatophytosis cannot be fully prevented, but the risk decreases by avoiding contact with infected animals and shared bedding or grooming equipment, and by keeping the living environment clean and dry. Malassezia dermatitis is often harder to prevent structurally because the yeast is normally present on the skin; for breeds with skin folds or drooping ears, regular grooming as advised by your veterinarian helps prevent moisture and dirt from building up. For dogs with a known underlying allergy, good management of that allergy helps limit repeated yeast overgrowth.

Living with a fungal infection

Dermatophytosis fully resolves in most healthy dogs with proper treatment, although this can take several weeks to months. Malassezia dermatitis more often has a recurring nature, especially when the underlying cause is chronic, such as an allergic predisposition. In these dogs, a long-term maintenance routine with periodic grooming may be needed to keep symptoms under control. Regular contact with your veterinarian helps adjust the approach as symptoms change.

Frequently asked questions

Is a fungal infection in dogs contagious?
Dermatophytosis (ringworm) is contagious between animals and can also spread to people. Malassezia dermatitis is an overgrowth of the dog's own skin flora and is not contagious.

Can I recognize a fungal infection in my dog by appearance alone?
Not with certainty. Other skin conditions can look similar, which is why examination by a veterinarian is needed for a reliable diagnosis.

Can I catch a fungal infection from my dog myself?
With dermatophytosis, that is possible, especially for children, the elderly and people with a weakened immune system. If in doubt, contact a doctor in addition to the veterinarian.

Why does a yeast infection keep coming back in my dog?
This often points to an underlying cause, such as an allergy or hormonal disorder, that does not go away on its own. A veterinarian can investigate what keeps triggering the yeast overgrowth.

Summary

Fungal infections in dogs cover two different conditions: the contagious, zoonotic dermatophytosis and the non-contagious Malassezia yeast overgrowth, which is usually linked to an underlying problem. Both forms can be distinguished well with targeted diagnostics and are generally treated successfully with the right, veterinarian-determined treatment.

One more thing

One more thing: this article does not replace a visit to the veterinarian. Fidello does not provide diagnoses or prescribe treatments. If in doubt, in case of persistent symptoms, or urgent signs, a veterinarian is always the right next step.