An increased incidence of dermal abnormalities is reported in patients with thyroid diseases. They can be due to altered metabolic activity, to autoimmune phenomena or to effects of T3 at the site of the target organ. In the hamster ear model it was demonstrated that thyroid hormones have effects on the mitotic activity and the size of the sebaceous glands but not on the de novo lipogenesis. These results are suggestive that the dry and scaly skin in hypothyroidism might not only be due to thyroid hormone action on sebaceous glands.