That chill in the hallway owes more to plumbing than to poltergeists. In many buildings, water pipes and ventilation shafts generate low-frequency infrasound, often below 10 hertz, that the ear barely registers yet the body still detects through subtle vibration and pressure shifts.
What feels like a haunted presence is in fact a stress experiment you never signed up for. Research on acoustic exposure shows that sustained infrasound can raise cortisol in saliva, a direct marker of hypothalamic–pituitary–adrenal activation, while subjects report irritability, fatigue and vague anxiety when those frequencies are present but not consciously heard.
The more persuasive story is biological, not supernatural. Below the threshold of clear hearing, mechanoreceptors in the inner ear and even visceral organs respond to pressure waves that ride through walls and floors, feeding the autonomic nervous system and biasing it toward a mild fight-or-flight state that people then label as dread, a presence, or a sense of being watched.
Ghost tours rarely mention boiler rooms, yet that is where much of this effect starts. Building acoustics specialists point to long metal runs, loose fixtures and turbulent water flow as efficient infrasound emitters, turning ordinary infrastructure into a background signal that quietly primes nerves before any story about spirits enters the room.
