Final answer:
When stressed, our body releases adrenaline and cortisol as part of the fight-or-flight response. The skin emits sweat from apocrine glands which, under stress, can result in body odor that may act as a human pheromone response.
Step-by-step explanation:
When we are stressed, our body's sympathetic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are activated. The sympathetic nervous system triggers a quick response, releasing adrenaline from the adrenal glands that increases heart rate and respiration. Meanwhile, the HPA axis releases corticotropin-releasing factor (CRF) from the hypothalamus, which causes the pituitary gland to release adrenocorticotropic hormone (ACTH). The ACTH then prompts the adrenal glands to secrete hormones, notably cortisol, which aids in responding to stress by boosting energy, but can also suppress the immune system if levels remain elevated. The skin, as a part of the body's first line of defense, secretes various fluids like sweat and sebum, which contain chemicals to kill pathogens and also react to emotional stress. Specifically, apocrine sweat glands, which are present in areas like the armpits, release a type of sweat that includes organic compounds. Under stressful conditions, this sweat can become thicker and its composition can result in body odor due to bacterial decomposition. Though not explicitly repelling a specific entity, this body odor can be off-putting to humans and is hypothesized to play a role in the human pheromone response.