The alarm stage is the first phase of the body’s stress response, known as General Adaptation Syndrome (GAS). It’s the immediate, automatic reaction your body launches when it detects a threat, whether that’s a near-miss car accident, a sudden loud noise, or any physical or psychological stressor. Endocrinologist Hans Selye first described this concept in a 1936 letter to the journal Nature, based on experiments showing that the body reacts to all kinds of harmful agents with the same predictable pattern: alarm, resistance, then exhaustion.
How the Alarm Stage Works
The alarm stage begins before you’re even consciously aware something is wrong. When your eyes or ears detect danger, the information travels to the part of your brain that processes emotions. That region instantly sends a distress signal to the hypothalamus, your brain’s command center for hormones. The wiring is so fast that this cascade starts before the visual processing centers of your brain have fully registered what’s happening.
From there, the response unfolds in two waves. The first is rapid: your adrenal glands flood your bloodstream with adrenaline and noradrenaline. This triggers a near-total activation of your sympathetic nervous system, the branch responsible for “fight or flight.” The second wave is slower. As the initial adrenaline surge fades, the hypothalamus activates a hormonal chain that ultimately causes your adrenal glands to release cortisol, which sustains the stress response over a longer period.
Two Sub-Phases: Shock and Countershock
The alarm stage itself contains two distinct sub-phases. The first is the shock phase, a brief window where the body’s defenses actually dip. Body temperature, blood pressure, and muscle tone all drop, and fluid shifts out of body tissues. This is the momentary vulnerability before your defenses kick in.
The countershock phase follows almost immediately, as the sympathetic nervous system ramps up and stress hormones surge. This is where the classic fight-or-flight response takes over, reversing the initial shock and mobilizing your body for action.
What Happens in Your Body
The physical changes during the alarm stage are dramatic and widespread. Your heart rate spikes, blood pressure rises, and blood flow redirects toward your muscles and brain, away from organs that aren’t needed for immediate survival like your digestive system. Research on emergency alarm responses found that heart rate can jump from a resting rate of around 59 to 74 beats per minute up to 111 to 122 beats per minute within seconds of an alarm. In professional firefighters, increases of 47 to 61 beats per minute within 30 seconds have been observed.
Your liver plays a critical role in fueling this response. Adrenaline and noradrenaline signal the liver to break down stored glycogen into glucose and release it into the bloodstream, giving your muscles and brain an immediate energy supply. Blood glucose levels rise, and the rate at which your cells burn energy increases across the board. Your blood also begins clotting faster, a built-in safeguard against potential injury.
At the same time, digestion essentially shuts down. Stress hormones bind to receptors throughout the gastrointestinal tract, slowing stomach emptying, reducing intestinal movement, and constricting blood vessels that supply the gut. This is why acute stress often causes nausea or a “knot” in the stomach. Your airways widen to take in more oxygen, your pupils dilate, and your mental state shifts toward heightened alertness, sharper focus, and even a temporary reduction in pain sensitivity.
Selye’s Original Observations
Selye discovered the alarm reaction by exposing rats to a range of harmful agents: cold, surgical injury, excessive exercise, and near-toxic doses of drugs. Regardless of what the stressor was, the animals showed the same trio of changes: enlarged adrenal glands (from overwork producing stress hormones), shrunken lymph nodes and thymus tissue (key parts of the immune system), and stomach ulcers. The fact that these responses were identical no matter what caused them was Selye’s breakthrough insight. He called it a “nonspecific adaptive response,” meaning the body treats all serious threats the same way during this initial stage.
This concept built directly on the earlier work of physiologist Walter Cannon, who had already described how adrenaline and noradrenaline drive fight-or-flight reactions. Selye expanded the picture by showing that the adrenal glands also release a different class of hormones, cortisol and related steroids regulated by the pituitary gland, that sustain the body’s defenses well beyond that initial adrenaline rush.
How the Alarm Stage Differs From Later Stages
The alarm stage is meant to be temporary. If the stressor continues, your body shifts into the resistance stage, where it attempts to adapt and cope at a more sustainable level. Cortisol and other hormones remain elevated but stabilize, and the body tries to return its other systems toward normal functioning while still managing the ongoing threat. If the stressor persists long enough that these adaptive resources are depleted, the body enters the exhaustion stage, where its ability to resist breaks down and the risk of illness rises sharply.
The key distinction is that the alarm stage is an all-out mobilization. It’s the body pulling every available lever at once: dumping stored energy into the blood, diverting blood flow, accelerating heart rate, and sharpening mental focus. The resistance stage, by contrast, is the body trying to settle into a sustainable defensive posture rather than running at full emergency capacity.
Why Repeated Alarm Responses Matter
In a single, short-lived episode, the alarm stage is protective. It’s the system that lets you leap out of the way of a car or react instantly to danger. The problem arises when this response fires repeatedly or doesn’t fully shut off. Each activation floods your body with adrenaline and cortisol, raises blood pressure, elevates blood sugar, suppresses digestion, and redirects blood flow away from non-essential functions.
Selye’s original research connected chronic activation of this stress pathway to a striking range of conditions: high blood pressure, stomach ulcers, kidney disease, arthritis, and asthma. His animal studies showed visible damage to immune tissue (the thymus and lymph nodes shrank) and erosion of the stomach lining, even when the stressor itself didn’t directly target those organs. The repeated redirection of blood away from the gut, combined with elevated stomach acid and reduced protective secretions, helps explain why chronic stress is so closely linked to gastrointestinal problems. Meanwhile, the sustained elevation of blood sugar and blood pressure from frequent alarm responses creates the metabolic conditions associated with cardiovascular disease over time.