Introduction:
The thyroid gland is a butterfly-shaped gland in the neck, located below the voice box (larynx) and above the trachea (windpipe). The thyroid gland produces thyroid hormones, an essential aspect of the endocrine system. The body's endocrine system has various hormones that regulate the metabolism of carbohydrates, proteins, and fats and other functions regulating heart rate, body temperature, etc.
How Do Thyroid Hormones Work?
T3 and T4 are produced from the thyroid follicles of the gland. The T3 and T4 are carried in general circulation in association with plasma proteins, especially thyroid-binding globulin. Most of the T3 and T4 are binding with thyroid-binding globulins. Less than 1 percent of T3 and T4 circulate freely in the body. The thyroid hormones work on every cell of the body. Usually, the T4 is converted into T3 while acting on the receptors in the cell. There is very little T4 that works on the receptors.
The thyroid gland releases thyroxine (T4) into the bloodstream, and it is transformed into T3 triiodothyronine through a process called de-iodination. The cells that have specific receptors that receive the effect of thyroid hormone and are better able to utilize the T3 than T4 hormones. So T4 hormones are considered an inactive form of thyroid hormone, and T3 hormone is considered an active form.
The following organs and glands convert T4 into T3-
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Muscles.
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Pituitary gland.
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Kidney.
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Liver.
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Thyroid.
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Adipose fat tissue.
Thyroid hormones have actions on every cell and all the organs in the body. Its actions include-
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Increases and decreases the heart rate.
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Regulates the temperature by increasing and decreasing body temperature.
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Movement of food in the digestive tract.
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Plays a role in brain development.
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Controls muscle contraction.
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Manages skin and bone regeneration.
What Are the Actions of Thyroid Hormones on the Skin?
Thyroid hormones are important for epidermal (a layer of skin) homeostasis. Epidermis is a barrier of the skin composed of self-renewing stratified squamous epithelium. By binding to the thyroid hormone receptors, the thyroid hormones regulate epidermal cell proliferation, homeostasis, and differentiation. The genes responsible for thyroid function are expressed on the skin. So normal levels of thyroid hormones are essential for skin physiology and homeostasis. The thyroid hormone is a crucial element in skin development and function involving epidermal proliferation, hair growth, differentiation, and wound healing. The thyroid hormone performs many vital functions that help with temperature, skin health, and metabolism.
How Does Hyperthyroidism Cause Thyroid Rash?
When the thyroid gland produces too many thyroid hormones, it is called hyperthyroidism. The conditions that cause hyperthyroidism are overactive thyroid nodules, food containing iodine, medicines that contain iodine, using nicotine products, pregnancy, type 1 or type 2 diabetes, thyroiditis (inflammation of the thyroid gland), and Grave’s disease (an autoimmune disorder that attacks the thyroid gland leading to the overproduction of thyroid hormones). The complications of hyperthyroidism include heart-related problems because thyroid hormones regulate heart rate. They cause thinning of bones, muscle problems, and an eye disease called Graves’ ophthalmopathy. Hyperthyroidism leads to the development of rash and skin issues. The rash appears at the creases of the skin, which is very itchy and painful. These rashes appear to develop rapidly with patches of raised red skin with itching and burning sensation. The itchy rash occurs at the back, face, neck, chest, and buttocks. The other skin changes are-
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Dark skin on the palm of hands, gums, and mouth.
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Deep lines on the soles of the palms and feet.
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Painless lumps and patches of scaly skin that feels hard and waxy.
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Dry skin with deep scales and cracks.
How Does Hypothyroidism Cause Rash?
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Hypothyroidism is a condition where there is low production of thyroid hormones. Graves’ dermopathy, also known as Pretibial myxedema, affects the skin.
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In this disease, there is a build-up of sugar compounds and carbohydrates deep within the skin and tissues.
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It affects the lower limbs causing lumps, swelling, and plaques. Myxedema means swelling of tissues under the skin.
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Pretibia refers to the region below the knee. Pretibial myxedema is common among people with hypothyroidism. They are characterized as raised, thick, scaly plaques formed on the skin in addition to edema (swelling) of the leg.
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The skin and hair follicles of the legs have a shiny, waxy texture like orange peel—the skin color changes from yellow to brown and purple.
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This condition happens if there is sugar buildup underneath the skin and if the body does not have enough thyroid hormones, it leads to this condition.
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Thyroid hormones prevent the sugar compound from building up under the skin.
What Are the Autoimmune Diseases That Cause Thyroid Dysfunction?
In autoimmune thyroid disease, the body’s immune system attacks its thyroid gland with autoantibodies.
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These autoantibodies are immune proteins that cause recurrent attacks on the skin, known as flares.
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The autoimmune thyroid disease can cause either hyperthyroidism or hypothyroidism. Autoantibodies target a specific receptor in the tissues under the skin that produces a flare. They turn on the protein known as IgE (immunoglobulin E), leading to allergic reactions because IgE is the antibody responsible for allergic reactions in the body.
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Other autoimmune thyroid diseases include painless thyroiditis. Subacute thyroiditis (thyroiditis due to viral infection), postpartum thyroiditis (thyroid gland gets inflamed after pregnancy leading to hyperthyroidism followed by hypothyroidism).
What Is the Treatment for Thyroid Rashes?
Corticosteroid injections, topical medications, and other anti-inflammatory medications can also help. For a pretibial myxedema rash, the underlying hyperthyroidism or Graves' disease must be treated with,
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Anti-thyroid medications such as Tapazole (methimazole), PTU (propylthiouracil), and Neo-Mercazole (carbimazole).
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Levothyroxine is a synthetic hormone that treats hypothyroidism.
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Corticosteroids like Prednisolone.
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Radioactive iodine
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Surgical ablation or partial removal of the thyroid gland.
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Some examples of thyroid hormone replacements are
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Levothyroxine, a synthetic form of T4 (Levoxyl, Unithroid)
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Liothyronine, a synthetic form of T3 (Cytomel).
Topical anti-itch creams are-
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Topical 1 percent hydrocortisone cream.
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Antihistamine creams like Benadryl itch-stopping cream.
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Lidocaine cream.
Antihistamines treat allergic reactions to the skin. The following are some of the anti-histamines-
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Claritin (loratadine).
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Allegra (fexofenadine).
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Zyrtec (Cetrizine).
Conclusion:
The thyroid hormone is an essential hormone that affects many aspects of the body. Some individuals with thyroid conditions experience skin rashes caused by an autoimmune response and in some cases, the rash may be a result of an allergic reaction to medication. It is important to consult with a healthcare professional if the person is experiencing skin rashes in conjunction with thyroid symptoms.
