Our bodies are remarkably intelligent systems, continuously translating our emotional experiences into physical reactions. One of the most striking examples of this mind-body dialogue is what medicine calls “sickness behaviour.” We’ve all felt it—the fatigue, fever, and body ache that push us to rest when we’re ill. These symptoms are not mere inconveniences but signs of immune system activity: cytokines, small protein messengers released by immune cells, prompt changes in our brain that conserve energy and aid recovery. However, when this biochemical dialogue becomes misdirected or prolonged, it can lead to chronic fatigue, emotional imbalance, and impaired immunity.
The Immune System as a Second Brain
It might surprise us to learn that immune cells such as lymphocytes can produce nearly all the same messenger chemicals—hormones, neurotransmitters, even endorphins—that the brain uses. These cells also carry receptors for brain-derived substances, revealing a two-way communication channel. This close biochemical relationship forms part of what is now known as psychoneuroimmunology (PNI)—the study of how the mind, the nervous system, and the immune system are intertwined.
At the centre of this network lies the hypothalamic-pituitary-adrenal (HPA) axis, the body’s chief stress-response system. The HPA axis integrates signals from both psychological and physical stressors and coordinates the appropriate hormonal responses.
The HPA Axis and the Stress Response
When the brain perceives a threat, the limbic system—its emotional processing centre—alerts the hypothalamus. The hypothalamus then stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). This hormone travels through the bloodstream to the adrenal glands, prompting the release of cortisol, a steroid hormone that mobilizes energy and suppresses nonessential functions in times of stress.
Simultaneously, the sympathetic nervous system activates the adrenal medulla to secrete adrenaline, the famed “fight-or-flight” hormone—speeding up the heart, sharpening alertness, and preparing the body for immediate action. While these responses are lifesaving during acute threats, ongoing stressors—especially those rooted in psychological factors like uncertainty, conflict, or lack of control—can keep the HPA axis chronically activated, disrupting hormonal balance and immunity.
Interestingly, a sense of control or resolution—what biologists term consummatory behaviour (from the Latin consummare, “to complete”)—instantly reduces HPA activity. When threats are removed, or emotional needs like love and belonging are met, the stress response naturally diminishes. On the other hand, unmet emotional needs or prolonged feelings of helplessness sustain stress chemistry, setting the stage for disease.
Emotions, Stress, and Cancer
PNI research helps explain why some individuals develop illnesses like cancer while others, exposed to the same carcinogens, do not. While factors like tobacco can directly damage DNA, those mutations alone rarely lead to tumours. The body’s repair mechanisms, immune surveillance, and programmed cell death, known as apoptosis, usually eliminate damaged cells before they multiply uncontrollably.
However, chronic stress and emotional repression can interfere with these protective systems. Prolonged release of stress hormones—particularly cortisol—can disturb the regulation of apoptosis, allowing abnormal cells to survive. Natural killer cells, vital components of our immune defense, become less active under stress. Thus, cancer initiation may require both genetic damage and a compromised physiological environment that fails to eliminate abnormal cells.
Once malignant cells form, their growth and spread are influenced by hormones. Many cancers—including breast cancers—are hormone-dependent. These cells carry receptors for hormones such as estrogen, progesterone, and prolactin, all of which can promote tumour growth. Because the HPA axis directly regulates these hormones, it becomes clear how emotional stress, via hormonal modulation, can influence disease progression.
Lessons from Social Stress
Animal studies vividly illustrate this connection. In groups of female monkeys where social hierarchies were disrupted, previously dominant females forced into subordination showed significant hormonal imbalances. Their cortisol levels rose while ovarian function declined, leading to irregular menstrual cycles. Meanwhile, monkeys that regained dominance displayed normal hormonal rhythms. These findings emphasize how social status, control, and emotional state directly shape endocrine and reproductive health.
The Healing Power of Awareness
In essence, the dialogue between mind and body is continuous and powerful. Stress, emotions, and immunity are not separate but part of one integrated conversation. Chronic emotional distress or repression sustains a biochemical environment that impairs cellular repair and regulation, increasing disease vulnerability. Conversely, emotional expression, supportive relationships, rest, and self-awareness foster a healthy balance within the HPA axis, strengthening both body and mind.
Understanding “sickness behaviour” and the psychoneuroimmunological web reminds us that healing begins not only with medicines but also with restoring harmony between our inner and outer worlds—where emotion, thought, and biology speak the same language.
Source : When the Body Says No: The Cost of Hidden Stress by Gabor Maté
Goodreads : https://www.goodreads.com/book/show/450534.When_the_Body_Says_No
Read the Previous Article in the Series :
Thinking Beyond Science 
Leave a comment