The ageing process tends to predispose dogs and cats to certain skin diseases. Impaired immunosurveillance is believed to render the animals more susceptible to neoplasia which can affect any organ including the skin. Endocrinopathies are also more common in older animals. There are some diseases of internal organs which can affect the skin, and some of these tend to occur with increased frequency in old animals. Finally, seborrhoeic diseases are either more common in older animals, or become increasingly severe with age.