Engert et al. (2014) found that empathic stress produces measurable cortisol increases in observers and that the magnitude of this endocrine response depends on emotional closeness to the person in distress and on the modality of observation. The Max Planck Institute issued a summary emphasizing stress contagion and interpersonal factors that shape physiological empathy.
Engert, Plessow, Miller, Kirschbaum, and Singer (2014) reported that observers exhibit cortisol increases in empathic stress and that those hormonal responses are modulated by emotional closeness to the target and by the observation modality (how the stressful event is perceived).
Sources:
Engert, Plessow, Miller, Kirschbaum, Singer (2014). Cortisol increase in empathic stress is modulated by emotional closeness and observation modality. Psychoneuroendocrinology.
pubmed.ncbi.nlm.nih.gov/2484…
Max Planck Institute summary:
mpg.de/research/stress-empat…