We’ve all heard how life-altering accidents or emotional upheavals can be, but a recent study by the University of Toronto, published in Current Biology, reveals something deeper. Even fully healed injuries — physical or emotional — can leave lasting marks on the body, increasing sensitivity to stress long after the visible wounds have faded.
The study offers new insights into how past trauma can reprogram both the nervous and immune systems, making individuals more vulnerable to future stressors, explains Dr Krupan Kumar, senior consultant, internal medicine, Apollo Hospitals, Hyderguda.
Dr Dilip Gude, senior consultant physician at Yashoda Hospitals, Somajiguda, elaborates, “In the study, researchers used mice models and observed that predatory fear experienced six months earlier still triggered stress responses. They identified a specific receptor — TRPV1 — as a key player in this reaction.”
But does this apply to humans? “Yes, to some extent,” Dr Dilip says, adding, “There are many cases where emotional trauma from years ago still manifests as physical and psychological symptoms — palpitations, anxiety, insomnia, depression, or a persistent sense of doom. Even minor triggers, like a smell, sound, or colour, can bring buried emotions to the surface.” While findings from mice can’t be directly applied to humans just yet, they offer important clues. “We need further research, particularly large-scale randomised control trials, to fully understand how this translates to humans,” he notes.
Dr Krupan highlights how this study goes beyond previous understanding. “Traditionally, we’ve known psychological stress slows wound healing. But this study is among the first to explore how past injuries can permanently alter the body’s stress response. Researchers found that old wounds can ‘prime’ the body’s stress axes, especially the hypothalamic-pituitary-adrenal (HPA) axis, which regulates cortisol, making individuals more reactive to future stress,” shares Dr Krupan.
These changes appear to affect both the central nervous system and the immune system, increasing threat sensitivity while lowering resilience. “This aligns with PTSD research, where trauma causes long-lasting epigenetic changes like methylation of stress-regulating genes which can even be inherited,” he adds.
Even when someone appears physically healthy, they may carry invisible scars from old trauma. “These hidden wounds could explain why some people experience chronic inflammation, delayed healing, or weakened immune responses without any obvious cause,” Dr Krupan says.
He believes the research adds a crucial dimension to our understanding of healing, “It’s not just ongoing stress that hinders recovery — past injuries may predispose the body to an exaggerated stress response. Previous studies have already shown that people under emotional strain, such as caregivers or those in difficult relationships, heal nearly twice as slowly.”
Given the complex feedback loop between past trauma and stress, Dr Krupan advocates for a more holistic treatment approach. “Physical care must go hand-in-hand with psychological support, stress-reduction techniques, and even medications that modulate stress-related hormones like cortisol or oxytocin,” says Dr Krupan.
So, what can be done to prevent or minimise these long-term effects? Dr Dilip suggests desensitisation. “For example, someone with a fear of heights from a past trauma could undergo ‘flooding’ — a process where they are gradually re-exposed to heights. Over time, this can reduce the phobia,” he notes.
Similarly, emotional triggers such as grief can be addressed through therapy. “Confronting and processing trauma, rather than avoiding it, is essential,” he adds.
In more severe cases, if trauma leads to symptoms like palpitations or heightened sympathetic activity, medications may be necessary. “Yes, the findings are applicable to humans to a degree, but we must be cautious and avoid overgeneralisation. Each case is unique,” Dr Dilip emphasises.
As chronic trauma and unresolved emotional wounds become more prevalent, this study underscores the need to integrate emotional care into physical recovery. Understanding that ‘old wounds’ can still influence the body’s stress response could pave the way for more comprehensive, compassionate, and resilient healthcare in the years to come.