The thyroid gland produces hormones that regulate the body’s metabolism, affecting nearly every cell and organ system. When this gland becomes underactive (hypothyroidism), it results in a systemic slowdown of bodily functions. This hormonal deficiency significantly impacts skin health. These dermatological changes are often among the earliest and most noticeable signs of an underlying thyroid imbalance.
How Thyroid Hormones Regulate Skin Function
The active thyroid hormone, triiodothyronine (T3), regulates metabolic activity within the skin. T3 and its precursor, thyroxine (T4), influence cellular oxygen consumption and the rate at which skin cells, or keratinocytes, grow and differentiate. Low thyroid hormone levels slow down the natural process of cell turnover in the epidermis, the outer layer of skin. This sluggish renewal rate contributes directly to the rough and scaly texture often observed in hypothyroid patients.
Thyroid hormones also regulate dermal fibroblasts, the cells responsible for producing structural components. A deficiency in T3 can lead to the accumulation of hydrophilic substances known as glycosaminoglycans within the dermis. Large amounts of hyaluronic acid are deposited, which binds substantial amounts of water. This accumulation creates a viscous environment that alters the skin’s texture and appearance.
Specific Cutaneous Manifestations
The most common skin finding associated with hypothyroidism is xerosis, or excessive dryness, often accompanied by scaling and a coarse texture. This dryness results from decreased secretion from the sebaceous and eccrine sweat glands, combined with slowed epidermal cell turnover. The skin may appear pale and cool to the touch due to reduced peripheral blood flow, as the body’s metabolic rate is lowered.
Myxedema is a distinctive manifestation, referring to the non-pitting swelling of the skin and underlying tissues. This swelling is caused by the water-binding properties of accumulated hyaluronic acid in the dermis, creating a doughy or waxy appearance, particularly around the eyes, hands, and lower legs. Unlike typical fluid retention, this type of swelling does not leave a temporary indentation when pressed.
Another subtle sign is carotenemia, a yellowish discoloration most apparent on the palms, soles, and nasolabial folds. This occurs because the body’s slowed metabolism is less efficient at converting beta-carotene, a pigment found in vegetables, into Vitamin A.
Changes to Hair, Nails, and Sweat Glands
Hypothyroidism frequently affects skin appendages, including hair, nails, and sweat glands, which rely on normal cellular metabolism for growth. Diffuse hair loss (alopecia) is common, resulting from the thyroid hormone’s influence on the hair follicle’s growth cycle. The hair that remains often becomes dry, coarse, and brittle due to structural changes and poor oil production. In some cases, patients may experience madarosis, the specific thinning or loss of hair from the outer third of the eyebrows.
Similarly, the nails are affected by the systemic slowing of cell proliferation, becoming brittle, thickened, and growing at a reduced rate. They may also develop longitudinal or horizontal ridges reflecting the compromised growth process. The eccrine sweat glands become less active (anhidrosis or hypohidrosis), which contributes to the overall dryness of the skin. This decrease in moisture production exacerbates the scaly, rough texture.
Resolving Hypothyroidism-Related Skin Issues
The primary method for resolving these dermatological issues is to treat the underlying hormonal deficiency with thyroid hormone replacement therapy, typically using synthetic T4 (levothyroxine). Restoring the circulating levels of T3 and T4 allows the body’s metabolism and cellular processes to return to normal function. While systemic symptoms like fatigue and cold intolerance often begin to improve within a few weeks, the skin, hair, and nail changes usually take longer to resolve.
It can take several months for the skin’s cell turnover and the hair growth cycle to fully normalize. The accumulated hyaluronic acid responsible for myxedema is slowly metabolized and cleared from the tissues once hormone levels are stable. Supportive care, such as using emollients and moisturizers, can provide temporary relief from xerosis while the body corrects the hormonal imbalance.