Stressed Out: Understand Your Stress Response

Stress is part of being human. Sometimes, it helps you act quickly in danger. Other times, it lingers and wears you down. Knowing how the stress response works can help you understand what your body is doing and why chronic stress can affect your health.

How the stress response starts

The process begins in the brain. The amygdala detects threat and signals the hypothalamus to activate the stress system. This sets in motion the hypothalamic pituitary adrenal axis, often shortened to HPA axis. The hypothalamus releases corticotropin releasing hormone, which cues the pituitary to release adrenocorticotropic hormone, which stimulates the adrenal glands to release cortisol. Cortisol then feeds back to help turn the system down when the threat passes (LeDoux, 2000; Karin et al., 2020; Sheng et al., 2021; Lightman et al., 2020).

Immediate chemical release

Within seconds the sympathetic adrenomedullary system triggers release of adrenaline from the adrenal medulla and noradrenaline from sympathetic nerve endings. Heart rate rises, blood pressure increases, and energy is mobilized so the body is ready for action. These fast changes support fight, flight, or freeze responses observed in humans and other animals (Becker et al., 2019; Paravati & Ponzio, 2022; Roelofs, 2017).

Sustained stress response

If the challenge continues, the adrenal glands release cortisol. Cortisol keeps glucose available to fuel the brain and muscles and temporarily downshifts digestion, reproduction, growth, and some immune activity so resources go to survival (Sapolsky, 2004; McEwen & Akil, 2020).

Secondary effects

Stress alters more than adrenaline and cortisol. Dopamine and serotonin can shift during persistent stress and are linked with anxiety and depression in a subset of people, often through inflammatory pathways (Kim et al., 2022; Hassamal et al., 2023). Endogenous opioids such as beta endorphin can be released during acute stress and can blunt pain, a phenomenon called stress-induced analgesia (Pilozzi et al., 2020; Nakamoto et al., 2023).

Recovery

When safety returns, the parasympathetic nervous system supports a return to baseline. Vagal activity increases, cortisol falls, heart rate slows, and digestion and immune function resume normal patterns. Stronger vagal regulation is associated with better emotion regulation and recovery after stress (Laborde et al., 2018; Thayer et al., 2021; Waxenbaum & Reddy, 2023).

Chronic stress

When stress does not turn off, the system can become dysregulated. Prolonged exposure to cortisol and repeated activation of threat circuits are associated with a higher risk for anxiety, depression, cardiovascular disease, obesity, diabetes, and immune problems. Chronic stress is also linked with changes in brain regions involved in memory and learning, including reduced hippocampal volume in some studies (McEwen, 1998; Lupien et al., 2009; Grupe et al., 2022; Girotti et al., 2024; Zhang et al., 2024).

Stress is natural. The problem is not stress itself, but when stress never resolves. Understanding your biology is the first step toward practices that restore a sense of safety, connection, and steadiness.

References

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