Stress triggers the release of several hormones, but the two main ones are cortisol and adrenaline (epinephrine). Adrenaline acts within seconds, accelerating your heart rate and sharpening your senses. Cortisol follows minutes later, flooding your bloodstream with glucose for sustained energy. Together, they form the body’s built-in survival system.
The Two-Phase Stress Response
Your body doesn’t release stress hormones all at once. It runs a two-stage process, each controlled by a different branch of your nervous system.
The first phase is the fight-or-flight response, driven by adrenaline and its close relative noradrenaline (norepinephrine). When your brain perceives danger, a region called the hypothalamus sends signals down your spinal cord and out to your body in a matter of seconds. The physical changes are immediate and dramatic: your pupils dilate to take in more light, your heart pumps harder to push oxygenated blood to your muscles, your airways open so you breathe deeper and faster, and your liver converts stored energy into glucose. Blood even diverts away from your skin toward your muscles, which is why people sometimes look pale when frightened.
The second phase produces cortisol through a slower, more deliberate hormonal chain reaction. This is the sustained stress response, designed to keep your body fueled and alert for minutes to hours rather than just seconds.
How Cortisol Gets Released
Cortisol production follows a specific cascade known as the HPA axis, named for the three structures involved: the hypothalamus, the pituitary gland, and the adrenal glands. In response to stress, your hypothalamus releases a signaling hormone that tells your pituitary gland to release another signaling hormone, which then tells your adrenal glands (small organs sitting on top of your kidneys) to produce cortisol.
This chain reaction takes a few minutes to complete, which is why cortisol is considered the body’s longer-acting stress hormone. While adrenaline handles the initial burst of energy, cortisol keeps glucose levels elevated so your body has a continued fuel supply. It influences glucose metabolism across multiple systems at once: your liver, muscles, pancreas, and fat tissue all respond to cortisol’s signal to mobilize energy stores. The overall effect is catabolic, meaning cortisol breaks down stored energy reserves to make them immediately available.
Cortisol’s Effects Beyond Energy
Cortisol does more than provide fuel. It also suppresses your immune system by dialing down inflammation. In the short term, this is useful. Your body is essentially saying, “We’ll deal with infections later; right now, survival is the priority.” But when cortisol stays elevated for weeks or months due to chronic stress, that immune suppression becomes a liability. You get sick more easily and recover more slowly.
Cortisol also follows a natural daily rhythm even when you’re not stressed. Levels are highest in the early morning (roughly 10 to 20 micrograms per deciliter around 6 to 8 a.m.) and drop to their lowest point around midnight (3 to 10 mcg/dL by late afternoon). This rhythm is what helps you feel alert when you wake up and wind down at night. Chronic stress disrupts this pattern, keeping cortisol artificially high when it should be falling.
Other Hormones Involved in Stress
Cortisol and adrenaline get the most attention, but stress activates a few supporting hormones as well. Aldosterone, released by the same adrenal glands that produce cortisol, tells your kidneys to hold onto sodium, which pulls water back into your bloodstream and raises blood pressure. Vasopressin (also called antidiuretic hormone) works alongside aldosterone to retain fluid. Together, they ensure your blood volume stays high enough to deliver oxygen to your muscles during a crisis.
This is why chronic stress can contribute to high blood pressure over time. These fluid-retention hormones are meant for short bursts, not daily activation.
What Happens When Cortisol Stays High
Short-term cortisol spikes are normal and healthy. The problems begin when stress becomes chronic, keeping cortisol elevated for months or years. One of the most well-documented consequences involves the hippocampus, a brain region critical for memory and learning. Research from Weill Cornell Medicine found that people with prolonged cortisol elevations had measurably smaller hippocampal volume and performed worse on memory tasks compared to those with normal cortisol levels. The degree of shrinkage correlated directly with how high and how long cortisol had been elevated.
Beyond the brain, chronically high cortisol promotes fat storage (particularly around the midsection), raises blood sugar, weakens bones, and thins skin. It also disrupts sleep, partly because elevated evening cortisol interferes with the natural drop your body needs to fall asleep.
Why Your Body Responds This Way
The stress hormone system evolved for physical threats: predators, injuries, scarcity of food. In those situations, a burst of adrenaline followed by sustained cortisol is exactly what keeps you alive. The problem is that your body can’t distinguish between a lion and a looming work deadline. Both trigger the same hormonal cascade, but one resolves in minutes while the other can persist for months. Your biology doesn’t have a separate system for psychological stress, so your organs, immune system, and brain absorb the consequences of hormones that were never designed to stay active this long.