The thyroid hormones affect nearly all tissues of the human body, including the skin. Skin tissues contain thyroid hormone receptors which, when occupied by thyroid hormones, stimulate cellular activity. Patients with hypothyroidism, or underactive thyroid disease, may experience skin symptoms that reflect diminished cellular skin activity in the absence of sufficient thyroid hormone. Some skin changes associated with hypothyroidism may cause itching. Hypothyroidism, which occurs most commonly among the elderly, affects an estimated 25 million people in the United States, reports the American Association of Clinical Endocrinologists.
Skin Dryness and Scaling
Up to 90 percent of patients with hypothyroidism experience skin dryness and scaling, reports endocrinologist Joshua Safer, M.D., of Boston University School of Medicine in the medical reference text "Werner & Ingbar's The Thyroid: A Fundamental & Clinical Text." When examined under the microscope, the skin of patients with hypothyroidism exhibits thinning and increased keratin, a protein found in the uppermost layer of the skin and in the hair and nails. The increased keratin and impaired shedding of old cells gives the skin a scaly appearance.
Decreased production of certain fats in the skin may contribute to skin dryness with hypothyroidism. Skin dryness in patients with hypothyroidism often proves worst on the palms, soles, elbows and knees, although the entire skin surface is typically involved. Dryness and scaling of the skin commonly causes itching. In patients with severe hypothyroidism-related skin dryness and itching, persistent scratching may lead to abrasions and localized infection.
Ichythyosis
Some patients with hypothyroidism develop a severe form of skin scaling known as acquired ichthyosis, reports the New Zealand Dermatological Society on the medical information website DermNet NZ. This condition represents a more advanced form of the scaling more commonly seen in patients with hypothyroidism. Itching frequently accompanies the scaling that characterizes acquired ichthyosis.
Hives
Patients with hypothyroidism may exhibit hives, or urticaria, which characteristically prove intensely itchy. In a 2006 article on the skin manifestations of hypothyroidism published in the "Indian Journal of Dermatology," Dr. Alka Dogra and colleagues report that approximately 16 percent of study patients exhibited hives. The authors note that the mechanism by which thyroid hormone deficiency provokes hives remains uncertain.
Blistering Rash
Dermatitis herpetiformis is a profoundly itchy, blistering rash that may occur in patients with hypothyroidism, notes "Werner & Ingbar's The Thyroid: A Fundamental & Clinical Text." Dermatitis herpetiformis --- which is unrelated to the herpes viruses --- typically affects the skin of the back, knees, elbows and buttocks on both sides of the body, reports the National Library of Medicine encyclopedia MedlinePlus.
References
- American Association of Clinical Endocrinologists: Hypothyroidism
- "Werner & Ingbar's The Thyroid: A Fundamental & Clinical Text, 9th Edition"; Lewis E. Braverman, M.D., Robert D. Utiger, M.D., Editors; 2005
- DermNet NZ: Ichthyosis
- "Indian Journal of Dermatology"; Thyroid and Skin; Alka Dogra, M.D., et al.; 2006
- MedlinePlus: Dermatitis Herpetiformis
