1 An adenoma is a part of the gland that has walled itself off from the rest of the gland, forming noncancerous (benign) lumps that may cause an enlargement of the thyroid. Not all adenomas produce excess T-4, and doctors aren't sure what causes some to begin producing too much hormone.  Thyroiditis.
Scratching Itchy Skin Causes Brain To Release Hormone Serotonin, Intensifies Itchy Sensation. While a good scratch may temporarily relieve you of your itch, it actually stimulates serotonin in the brain that intensifies the itchy feeling.
There are other causes of skin itching that are important. Common ones include thyroid problems (specifically hypothyroid -- which also gives constipation, feeling cold, tired), liver problems (sometime with yellowing of the skin). Dry skin is the most common cause -- in which the skin is scaly and falls off.