Cortisol is a steroid hormone produced in your adrenal glands. It can affect your body in a number of ways, including how your body responds to stress. When balanced, your cortisol levels will fluctuate throughout the day, starting higher in the morning, and getting lower in the evening. If your cortisol levels are too low in the morning or too high in the evening, it can have a negative impact on everything from your energy levels to your immune health.