Thyroid cysts are not contagious. They are fluid-filled sacs within the thyroid gland, usually presenting as a single nodule, although in some cases multiple nodules can occur. Typically, thyroid cysts are asymptomatic unless the cyst becomes large or bleeds internally. In such cases, symptoms such as pain, difficulty swallowing, breathing difficulties, and a hoarse voice may occur. Thyroid cysts are considered a local endemic disease primarily caused by iodine deficiency, leading to thyroid hyperplasia and enlargement. Thyroid cysts represent a degenerative change. Therefore, thyroid cysts are not contagious.