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.
An insect bites you by making a hole in your skin to feed. Most insects sting as a defence by injecting venom into your skin. Symptoms of an insect bite or sting. When an insect bites, it releases saliva that can cause the skin around the bite to become red, swollen and itchy. The venom from a sting often causes a swollen, itchy, red mark (a weal) to form on the skin. This can be painful, but it's harmless in most cases.