According to the National Institute of Diabetes and Digestive and Kidney Disorders (NIDDK), the thyroid gland makes two hormones (triiodothyronine and thyroxine) that affect the amount of moisture in the skin. These hormones also influence metabolism, body temperature, and blood, heart and nervous system functions that indirectly affect the skin. If the thyroid secretes too much or too little of these hormones, it can cause bothersome changes to the skin's overall health and texture.
Overactive Thyroid Effects
When the thyroid gland becomes overactive, it can cause a condition known as hyperthyroidism. According to the New Zealand Dermatological Society (NZDS), symptoms that may be related to an overactive thyroid gland include increased skin smoothness and moistness, warm skin, generalized itching (pruritus), hives (urticaria), increased skin pigmentation and a flushing of the face and hands. A specific type of hyperthyroidism caused by autoimmune dysfunction (Graves disease) can lead to vitiligo--a condition characterized by irregularly shaped white patches on the skin resulting from the destruction of pigment cells. Loss of skin pigment may occur on the face or neck, body folds (elbow, armpits, groin), sites of injury or around moles.
Underactive Thyroid Effects
An underactive thyroid can cause a condition known as hypothyroidism. Hypothyroidism can affect the skin in a number of ways. A condition known as carotenaemia may develop, characterized by the skin turning yellowish in color. The skin may also become cold, pale and dry. Dry skin may be more at risk for developing dermatitis, or an inflammation of the skin. Although there are many types of dermatitis, people with hypothyroidism may be likely to develop eczema craquelé (or Asteatotic Eczema)--a condition in which the skin becomes dry and itchy and cracks or splits open into irregular fissures. The eyelids and hands may become puffy and swollen, and wounds on the skin can take a long time to heal. The NZDS also notes that people with underactive thyroids may develop mucinoses--rare skin disorders caused by abnormal deposits of mucins (jelly-like connective tissue) in the skin.
According to the NZDS, a rare condition known as pretibial myxedema can sometimes occur as a result of hypothyroidism or hyperthyroidism. It occurs in roughly 5 percent of patients with Graves disease (an autoimmune condition that causes hyperthyroidism).
The condition is characterized by thickened and elastic skin on the lower extremities, although it may sometimes spread to the trunk, face and upper extremities. Initial symptoms often include a lumpy or swollen appearance on the shins or feet. The skin may turn pinkish or purplish in color and may have an orange peel appearance. Alternatively, some cases may cause skin changes that appear like wart-like lesions. Hair follicles can also become highly prominent and visible.