**3. Conclusions**

Thyroid autoimmunity is the most prevalent autoimmune condition in the general population, and is also associated with various skin diseases. The evidence is strong for the association with alopecia areata. Although their etiology is still unclear, the autoimmune hypothesis is most commonly accepted.

The nature of the relationship between anti-thyroid autoimmunity and the pathogenesis of autoimmune diseases is presently unknown. Some authors have shown that anti-Tg antibodies can form immune complexes [46], and anti-microsomal antibodies not only bind to thyroid peroxidase but also modulate natural killer cell activity in autoimmune thyroiditis [47]. Possible explanations for the relationship of these autoimmune diseases include: (1) immunomodulatory effects of antithyroid antibodies, (2) molecular mimicry between thyroid and disease-specific epitopes, and (3) genetic link between anti-thyroid autoimmunity and the susceptibility to autoimmune disease [48]. It is a multidisciplinary problem requiring cooperation of specialists in different fields of medicine. Both dermatologists and endocrinologists have to inquire their patients about the family history of autoimmune diseases and to look for associated autoimmune disorders.

This chapter is an attempt to update the current knowledge about the relationship between the thyroid and the skin diseases. Although cutaneous manifestations of autoimmune thyroid diseases are well described and thyroid hormone is known to regulate the development and function of skin, a better understanding of these processes is needed.
