Chronic seborrheic skin disease is aesthetically displeasing and can adversely affect the human–animal bond. Nonspecific descriptive terms such as seborrhea oleosa, seborrhea sicca, and seborrheic dermatitis are commonly used to describe seborrhea, but there is confusion around these terms. In veterinary medicine, seborrhea sicca is used to describe focal or diffuse scaling of the skin with the accumulation of white nonadherent scales and a dull dry coat. The opposite, seborrhea oleosa, refers to greasy skin and hairs.1 Many patients, however, have both flaky and greasy skin; thus, although these terms are descriptive, they may not be particularly helpful, as the conditions can be caused by a large number of underlying diseases.
Physicians use the term seborrheic dermatitis to refer to a chronic inflammatory disorder affecting areas of the head and trunk where, in humans, sebaceous glands are prominent.2 Veterinary clients may be frustrated when they present their pet for seborrhea treatment and are told that seborrhea is rarely a specific diagnosis but simply a descriptive term. They may fail to understand why a detailed history, examination, and further testing are necessary to determine the underlying cause.
When treating a patient with scaly or seborrheic skin, it is important to determine whether the scaling is a primary keratinization defect or secondary to another skin or internal disease. In primary keratinization disorders, the excessive scale is caused by a direct defect in one or more steps in stratum corneum formation. Secondary disorders (ie, those in which seborrhea develops as a result of another condition3) account for at least 80% of all seborrhea cases; it is critical to rule out such secondary disorders before diagnosing primary keratinization dermatoses.4
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Most cases of secondary seborrhea have a good prognosis if the underlying cause is identified and treated successfully. Primary keratinization diseases are more difficult to control and usually require lifelong management, which is often labor intensive and costly.