Cats with eosinophilic granuloma complex (EGC) may have one or more of four patterns of skin disease.

The most frequent form is "eosinophilic plaque". This is a rash comprising raised red to salmon-colored and flat-topped, moist bumps scattered on the skin surface. The most common location is on the ventral abdomen and inner thigh.

Another form of EGC is the "lip ulcer". This is a painless, shallow ulcer with raised and thickened edges that forms on the upper lip adjacent to the upper canine tooth. It is often found on both sides of the upper lips.

The third form of the EGC is the "collagenolytic granuloma". This is a firm swelling that may be ulcerated. The lesions may form on the skin, especially of the face, in the mouth, or on the feet, or may form linear flat-topped raised hairless lesions on the back of the hind legs, also called "linear granuloma".

The least common form of EGC is "atypical eosinophilic dermatitis". It is unique in that it is caused by mosquito bite allergy and the lesions form on the parts of the body with the least hair affording easy access to feeding mosquitoes. This includes the bridge of the nose, the outer tips of the ears and the skin around the pads of the feet. The lesions are red bumps, shallow ulcers and crusts.

Aside from the visible rash, granuloma annulare is usually asymptomatic. Sometimes the rash may burn or itch. People with granuloma annulare usually notice a ring of small, firm bumps (papules) over the backs of the forearms, hands or feet, often centered on joints or knuckles. The bumps are caused by the clustering of T cells below the skin. These papules start as very small, pimple looking bumps, which spread over time from that size to dime, quarter, half-dollar size and beyond. Occasionally, multiple rings may join into one. Rarely, granuloma annulare may appear as a firm nodule under the skin of the arms or legs. It also occurs on the sides and circumferential at the waist and without therapy can continue to be present for many years. Outbreaks continue to develop at the edges of the aging rings.

It begins as painless reddish-brown nodules which slowly enlarge to form irregularly shaped red plaque.

Localized granuloma annulare has a tendency towards spontaneous resolution. Localized lesions have been treated with potent topical corticosteroids.

Lupus vulgaris (also known as Tuberculosis luposa) are painful cutaneous tuberculosis skin lesions with nodular appearance, most often on the face around the nose, eyelids, lips, cheeks, ears and neck. It is the most common "M. tuberculosis" skin infection. The lesions may ultimately develop into disfiguring skin ulcers if left untreated.

Granuloma annulare in HIV disease is a skin condition characterized typically by papular and generalized skin lesions.

Perforating granuloma annulare is a skin condition of unknown cause, usually appearing on the dorsal hands, presenting as papules with a central keratotic core.

Annular elastolytic giant-cell granuloma (also known as "Giant cell elastophagocytosis," "Meischer's granuloma," "Miescher's granuloma of the face") is a cutaneous condition characterized histologically by a dermal infiltrate of macrophages.

In both healthy and immunocompromised hosts, Majocchi's granuloma often presents as nodules and papules on areas that are most exposed to mechanical abuse—wear and tear—such as the upper and lower extremities. Patients will complain about papules, pustules, or even plaques and nodules at the site of infection. The papules will be pink-red and will be located in a perifollicular location. Hair shafts can be easily removed from the pustules and papules. Itching is also very common. Firm or fluctuant subcutaneous nodules or abscesses represent a second form of MG that is generally observed in immunosuppressed hosts. Nodules may develop in any hair-bearing part of the body but are most often observed on the forearms, hands, and legs of infected individuals. Involvement of the scalp and face is rarely observed. Lesions start as solitary or multiple well-circumscribed perifollicular papulopustules and nodules with or without background erythema and scaling. In rare circumstances, the lesions may have keloidal features.

Eosinophilic granuloma is a form of Langerhans cell histiocytosis. It is a condition of both human and veterinary pathology. Colloquially, the reaction pattern is sometimes referred to as a rodent ulcer.

Feline eosinophilic granuloma complex is synonymous with "feline eosinophilic skin diseases". This is considered to be a cutaneous reaction pattern that can be the manifestation of a number of underlying infections, allergies or ectoparasite infestations. It can also be idiopathic, that is have no known underlying trigger. The eosinophilic reaction is common in feline inflammatory disease and the eosinophilic granuloma can be a hereditary reaction pattern in some lines of domestic cats.

Granuloma annulare is a fairly rare, chronic skin condition which presents as reddish bumps on the skin arranged in a circle or ring. It can initially occur at any age and is four times more common in females.

Patch-type granuloma annulare (also known as "Macular granuloma annulare") is a skin condition of unknown cause, more commonly affecting women between 30 and 70 years of age, characterized by flat or slightly palpable erythematous or red-brown skin lesions.

Fungal folliculitis (also known as Majocchi granuloma) is a skin condition characterized by a deep, pustular type of tinea circinata resembling a carbuncle or kerion.

Majocchi's disease (also known as Majocchi's Granuloma, "Purpura annularis telangiectodes,", and "Purpura annularis telangiectodes of Majocchi") is well-recognized but uncommon skin condition characterized by purple/bluish-red 1- to 3-cm annular patches composed of dark red telangiectases with petechiae. The name Majocchi's comes from the Professor Domenico Majocchi who first discovered the disorder in 1883. Domenico Majocchi was a professor of dermatology at the University of Parma and later the University of Bologna. Majocchi's disease can be defined as an infection of the dermal and subcutaneous tissues due to a fungal mold infection on the cutaneous layer of the skin. The most common dermatophyte is called "Trichophyton rubrum." This disease can affect both immunocompetent and immunocompromised hosts. However, immunocompromised individuals have a higher risk.

Subcutaneous granuloma annulare (also known as "Deep granuloma annulare," and "Pseudorheumatoid nodule") is a skin condition of unknown cause, most commonly affecting children, with girls affected twice as commonly as boys, characterized by skin lesions most often on the lower legs.

Generalized granuloma annulare is a skin condition of unknown cause, tending to affect women in the fifth and sixth decades, presenting as a diffuse but symmetrical, papular or annular eruption of more than ten skin lesions, and often hundreds.

Actinic granuloma (also known as "O'Brien granuloma") is a cutaneous condition characterized histologically by a dermal infiltrate of macrophages.

Actinic granuloma is an asymptomatic granulomatous reaction that affects sun-exposed skin, most commonly on the face, neck, and scalp.

It is characterized by annular or polycyclic lesions that slowly expand centrifugally and have an erythematous elevated edge and a hypopigmented, atrophic center.

Advise to reduce exposure to the sun and to use sunscreen.

Treatment with topical halometasone cream, pimecrolimus cream.

Aquarium granuloma (also known as "fish tank granuloma" and "swimming pool granuloma") is a skin condition caused by "Mycobacterium marinum", characterized by a skin lesion that presents roughly three weeks after exposure.

Angiolymphoid hyperplasia with eosinophilia (also known as: "Epithelioid hemangioma," "Histiocytoid hemangioma," "Inflammatory angiomatous nodule," "Intravenous atypical vascular proliferation," "Papular angioplasia," "Inflammatory arteriovenous hemangioma," and "Pseudopyogenic granuloma") usually presents with pink to red-brown, dome-shaped, dermal papules or nodules of the head or neck, especially about the ears and on the scalp.

It, or a similar lesion, has been suggested as a feature of IgG4-related skin disease, which is the name used for skin manifestations of IgG4-related disease.

The disease mimics many other dermatoses and can be confused with conditions, such as sarcoidosis, discoid lupus erythematosus, mycosis fungoides, and fixed drug eruption.

The appearance of pyogenic granuloma is usually a color ranging from red/pink to purple, and can be smooth or lobulated. Younger lesions are more likely to be red because of the high number of blood vessels. Older lesions begin to change into a pink color. Size commonly ranges from a few millimeters to centimeters, though smaller or larger lesions may occur. A pyogenic granuloma can be painful, especially if located in an area of the body where it is constantly disturbed. Pyogenic granulomas can grow rapidly and will often bleed profusely with little or no trauma. They may exude an oil like substance, causing the surface to be damp. This is especially true if the granuloma is located on the scalp.

Pyogenic granulomas may be seen at any age, and are more common in females than males. In pregnant women, lesions may occur in the first trimester with an increasing incidence up until the seventh month, and are often seen on the gums. Epulis granulomatosum is a variant of pyogenic granuloma that forms only on gingiva, and is often seen forming in a recent extraction socket. Pyogenic granulomas appear on the gingiva in 75% of cases, more often in the maxillary than mandibular jaw. Anterior areas are more often affected than posterior areas. It can also be found on the lips, tongue, and inner cheek. Poor oral hygiene or trauma are usually precipitating factors.

One study has suggested a correlation between pyogenic granulomas and Bartonella seropositivity. However, this association has been questioned by others. The microscopic appearance of a pyogenic granuloma consists of highly vascular granulation tissue. Inflammation is present. The lesion may have a fibrous character if it is older, and the surface may have ulcerations. Pyogenic granulomas rarely occur in the conjunctiva, cornea or connective tissue of the eye following minor local trauma. Grossly these mass lesions resemble those occurring at more common sites. The relationship of these lesion to lobular capillary hemangiomas of skin and oropharyngeal mucosa commonly referred to as pyogenic granuloma is uncertain.

Due to its overwhelming incidence on the gingiva, the condition is often associated with two other diseases, though not because they occur together. Instead, the three are associated with each other because they appear frequently on gingiva—peripheral giant cell granuloma and peripheral ossifying fibroma. Detailed analysis can be used to distinguish these conditions.

Lick granuloma is a form of self-trauma and skin disorder in which most commonly dogs, but also cats, continuously lick a small area of their body until it becomes raw and inflamed. The most common areas affected are the lower (distal) portions of their legs, such as the carpus (wrist), or sometimes another part of their body such as the base of their tail.

The lesion can initially be red, shiny, swollen, hairless, irritated, and bleeding, similar to a hot spot (wet eczema). Eventually a raised hard plaque forms.

NL/NLD most frequently appears on the patient's shins, often on both legs, although it may also occur on forearms, hands, trunk, and, rarely, nipple, penis, and surgical sites. The lesions are often asymptomatic but may become tender and ulcerate when injured. The first symptom of NL is often a "bruised" appearance (erythema) that is not necessarily associated with a known injury. The extent to which NL is inherited is unknown.

NLD appears as a hardened, raised area of the skin. The center of the affected area usually has a yellowish tint while the area surrounding it is a dark pink. It is possible for the affected area to spread or turn into an open sore. When this happens the patient is at greater risk of developing ulcers. If an injury to the skin occurs on the affected area, it may not heal properly or it will leave a dark scar.

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.