What is thyroxine? Thyroxine is a hormone that your thyroid releases into your blood, which helps to regulate many processes in the body, including your heart rate and your body’s ability to make repairs. It regulates bone growth, protein production, metabolic rate, and more. Almost every single cell in your body is affected in one way or another by this hormone that your thyroid releases—including your skin cells. In the next post, we will look at how thyroid issues can affect the health of your skin.