Thyroid Hormone Action on Skin

In the 2011 review by Joshua D. Safer, the complex effects of thyroid hormone on skin were explored, highlighting its direct action on skin tissues, its effects due to actions on non-skin tissues, and its role in autoimmune skin diseases linked to thyroid dysfunction. The review detailed how hypothyroidism typically results in rough, scaly skin and hyperthyroidism in smooth, thin skin, due to the presence of thyroid hormone receptors and responsive genes in skin cells. It was noted that hypothyroidism can cause the skin to appear pale because of increased dermal mucopolysaccharides and water content, particularly hyaluronic acid in myxedema. Thyroid hormone was found to stimulate dermal fibroblast proliferation and possibly influence wound healing, although this effect was debated. Additionally, thyroid dysfunction was associated with changes in hair and nails, with hypothyroidism leading to dry, brittle hair and nails, and hyperthyroidism causing fine hair and altered nails. The review also mentioned that sweat gland secretion is reduced in hypothyroidism, which might be due to atrophic glands and the accumulation of PAS-positive material. The review concluded that thyroid hormone's effects on the skin are multifaceted and could have therapeutic implications for skin conditions and wound healing.