Dermatology

Allergies are hypersensitivity reactions of the immune system to specific substances (allergens) from the environment or diet. In dogs, atopic dermatitis (environmental allergy) is one of the most common skin diseases; an estimated 10–15% of dogs suffer from allergic skin conditions. Animals with allergies often show intense itching and red, irritated skin, and ear infections or secondary infections are also frequently present. Management includes reducing exposure to allergens (for example, flea control or dietary changes), suppressing itch and inflammation with medication such as antihistamines or corticosteroids, and, where possible, desensitization through allergen-specific immunotherapy.

Itchy skin (pruritus) is one of the most common symptoms of dermatological problems in animals. Pets affected by pruritus frequently scratch, bite, or lick themselves, which can lead to redness, sores, and eventually areas of hair loss. Pruritus has many possible causes: parasites (such as fleas or mites) and allergies are common, but bacterial or fungal infections may also contribute. Addressing the underlying cause is essential, in addition to providing temporary relief with anti-pruritic treatments, so that scratching stops and the skin can heal.

Hair loss (alopecia) occurs when fur is lost in certain areas, leaving the skin visible. This may be localized or generalized and has various causes. Common reasons include chronic scratching or biting due to itch (for example, flea allergy or mange), fungal infections such as ringworm, or hormonal disorders (such as thyroid disease or Cushing’s disease). The skin in affected areas may appear red, scaly, or thickened. Effective treatment requires identifying and addressing the underlying cause, such as eliminating parasites, treating infection, or correcting hormonal imbalance, so that hair regrowth can occur.

Scaling skin and skin inflammation (dermatitis) often indicate disruption of normal skin health. Scaling (dandruff) results from accelerated shedding of the skin or accumulation of dead skin cells, as seen for example in seborrhea or after prolonged irritation. Dermatitis is usually accompanied by redness, warmth, swelling, and itching, and may be caused by allergies, infections, or a combination of both. Bacteria or yeasts often act as secondary invaders on already irritated skin, allowing a simple allergy to progress into a more extensive skin infection. Treatment focuses on eliminating the triggering cause (such as avoiding allergens or treating infection) as well as symptomatic skin care, for example with medicated shampoos to reduce scaling and anti-inflammatory topical treatments.

Ear infection (otitis externa) is a common problem, particularly in dogs, affecting an estimated 7–16% of dogs and approximately 4% of cats. Animals with otitis often show signs such as redness of the ear pinna, head shaking, pain on touch, and scratching at the ear. In most cases, external ear infection is secondary to an underlying cause, such as allergies, ear parasites (ear mites), or hormonal disorders. Bacteria and yeasts readily proliferate in the inflamed ear canal, worsening clinical signs by producing discharge and an unpleasant odor. Treatment consists of thorough cleaning of the ear canal and the use of ear drops with anti-inflammatory and antimicrobial properties. Addressing the underlying cause is essential to prevent recurrence.

Parasites such as fleas, mites, and ticks are a frequent source of skin complaints. Fleas often cause intense itching and may trigger an allergic reaction in sensitive animals (flea allergy dermatitis), leading to scratching, red papules, and crusts, especially on the back, abdomen, and base of the tail. Mites are microscopic arachnids that can cause various skin conditions. Sarcoptes mites cause severe itching and crusting dermatitis (sarcoptic mange), while Demodex mites inhabit hair follicles and may lead to hair loss and sometimes inflammation (demodicosis). Ear mites (Otodectes cynotis) reside in the ear canal and cause brown, crumbly discharge and pruritus. Ticks attach to the skin, causing local irritation and potentially transmitting infectious diseases. Prevention and control of parasites are essential and include regular flea and tick prevention as well as appropriate treatment, such as medicated shampoos, spot-on products, or oral medications, when a parasitic infestation is diagnosed.

Bacterial skin infections occur when bacteria penetrate the skin and cause inflammation with pus formation, a condition also known as pyoderma. Staphylococcal bacteria are the most common pathogens involved in skin infections in dogs and cats. These infections may present as red papules, pustules, crusts, or moist lesions, often accompanied by itching. Bacterial skin infections frequently develop secondarily, for example after self-trauma from scratching or when the skin barrier is compromised by another dermatological condition. Treatment involves targeted antimicrobial therapy, such as antibacterial shampoos or systemic antibiotics in severe cases, along with addressing the underlying cause to prevent recurrence.

Fungal skin infections are caused by dermatophytes, fungi that affect the skin, hair, or nails, or by yeasts. A well-known dermatophyte infection is ringworm in dogs and cats, which causes circular areas of hair loss with scaling and crusting. Ringworm is most commonly caused by fungi of the genus Microsporum, such as Microsporum canis, or Trichophyton species, and is zoonotic, meaning it can be transmitted to humans. Yeast infections, such as Malassezia dermatitis, also occur and result from overgrowth of normal skin yeasts, leading to red, greasy, and itchy skin, often in areas such as the groin, armpits, ears, or skin folds. Fungal infections are treated with antifungal therapies, which may be topical, for example shampoos, ointments, or sprays, and or systemic oral medication, depending on severity. In cases of ringworm, environmental hygiene is particularly important, as fungal spores can persist in the environment and cause reinfection.

Hormonal disorders (endocrine diseases) can have pronounced effects on the skin and coat of animals. A well-known example is hypothyroidism in dogs, in which symmetric hair loss often occurs, the coat becomes dry and dull, and the skin thickens and develops hyperpigmentation. Another example is hypercortisolism (Cushing’s syndrome), characterized by excessive production of the stress hormone cortisol. Dogs with Cushing’s disease often have thin, fragile skin with symmetrical hair loss on the trunk, sometimes accompanied by visible blood vessels and numerous comedones. Wounds tend to heal slowly, and calcification of the skin may occur. Imbalances in sex hormones can also result in hair loss or skin discoloration. Treatment of hormonally induced skin disease focuses on correcting the hormonal imbalance, for example through medication or surgery, after which skin abnormalities usually improve gradually.

Immune-mediated skin diseases are conditions in which the animal’s immune system mistakenly attacks its own skin cells or structures. This often results in severe skin inflammation with characteristic features. An example is pemphigus foliaceus, the most common autoimmune skin disease in dogs, cats, and horses. In pemphigus, superficial blisters and pus-filled vesicles develop and rapidly dry into crusts, particularly on the nasal bridge, around the eyes, ears, and sometimes the footpads. Other immune-mediated diseases, such as lupus or vasculitis, can cause skin ulcers, depigmentation, or thickened, scar-like lesions. These conditions are rare and usually chronic. Treatment consists of long-term administration of immunosuppressive medications, such as corticosteroids or other immunosuppressants, to dampen the abnormal immune response, often on a lifelong basis to prevent relapse.

The term skin mass refers to any abnormal lump or growth in or on the skin. This may be a benign lesion, such as a lipoma (fatty tumor) or a sebaceous cyst, but it can also be a malignant skin tumor, such as a mast cell tumor or melanoma. Non-neoplastic processes, such as inflammatory swellings or abscesses, may also appear mass-like. To determine the type of skin mass involved, the veterinarian will often collect cells from the lesion using a needle (fine-needle aspiration) or obtain a tissue sample via biopsy for examination. Based on the results, an appropriate treatment plan can be developed. Some harmless masses may be monitored, but in most cases surgical removal is recommended, especially for rapidly growing or malignant tumors.

Certain skin conditions or lesions require surgical treatment or specialized procedures. This category includes problems involving accumulations or damage that do not resolve spontaneously, or anatomical abnormalities that continuously cause skin issues. Examples include an ear hematoma, a subcutaneous abscess, or skin folds that become chronically inflamed. In such cases, timely surgical intervention can greatly promote healing and prevent recurrence.

An ear hematoma, also known as an aural hematoma or “blood ear,” is a collection of blood within the ear flap. A blood vessel inside the ear ruptures, causing blood to accumulate between the skin and cartilage, resulting in a soft, fluid-filled swelling. Ear hematomas usually develop as a result of vigorous head shaking or scratching due to ear pain or severe itch, for example from an ear infection or ear mite infestation. The ear becomes thickened and balloon-like and can be painful. Treatment typically involves surgically opening and draining the blood pocket, followed by placement of sutures or a pressure bandage to allow the skin to reattach to the cartilage. The underlying cause, such as an ear infection, must always be treated to prevent recurrence.

An abscess is a pus-filled cavity beneath the skin caused by a localized bacterial infection. In dogs and cats, abscesses often develop after bite wounds or other penetrating injuries, allowing bacteria to enter deep tissues and form a localized inflammatory response. This inflammation matures into a cavity filled with pus, consisting of bacteria, dead cells, and tissue debris. An untreated abscess may eventually rupture and drain externally, but it rarely heals completely on its own and often recurs as long as the source of infection remains.

In some breeds, such as Pugs, Bulldogs, or Shar-Peis, deep skin folds—for example facial wrinkles over the nose or a heavy tail fold—can lead to chronic irritation and skin inflammation. These folds are often warm and moist, creating an ideal environment for bacteria and yeasts that cause itching and infection. A well-known example is the nasal fold in Pugs, which frequently leads to painful skin inflammation and may require surgical removal. Skin fold resection involves excising the excess skin and suturing the edges together to create a smoother surface. This procedure is only performed when cleaning and topical treatments are insufficient and the animal suffers from persistent inflammation. After removal of the skin fold, the skin usually heals well and chronic symptoms resolve, significantly improving the animal’s quality of life.