Sepsis can and frequently does cause hallucinations, most often as part of a broader brain dysfunction called sepsis-associated encephalopathy, or SAE. This condition, which spans a spectrum from mild confusion to deep coma, affects up to 70% of sepsis patients admitted to intensive care units.1Neurotherapeutics. Septic-Associated Encephalopathy: a Comprehensive Review Hallucinations during sepsis are not rare complications or signs of a separate psychiatric illness. They are a recognized neurological consequence of the body’s overwhelming response to infection, and understanding how they happen changes how patients, families, and clinicians should approach them.
What Sepsis-Related Hallucinations Actually Look Like
When people hear “hallucinations,” they often picture the dramatic portrayals in movies. Sepsis-related hallucinations tend to be different. They are predominantly visual and are woven into a broader state of confusion, disorientation, and difficulty processing what is real. Patients with sepsis-associated delirium have reported seeing things that were not there, experiencing a distorted sense of their surroundings, and struggling to understand or communicate with healthcare providers.2PubMed. Bodily and Cognitive Experience in Patients With Sepsis and Delirium or Subsyndromal Delirium Some patients describe vivid scenes or figures that feel entirely real in the moment.
One detail from patient interviews stands out: people with sepsis-related hallucinations sometimes describe a gradual process of recognizing that what they are seeing is not real. They open their eyes, confront the visual stimuli, and slowly piece together that the experience is a hallucination rather than reality.2PubMed. Bodily and Cognitive Experience in Patients With Sepsis and Delirium or Subsyndromal Delirium This moment of reconnection can be an important turning point in recovery, but reaching it is not guaranteed. Some patients remain trapped in a confused state for days, unable to tell the difference between hallucination and reality, while others cycle in and out of clarity.
These experiences are deeply distressing. Patients frequently recall them after discharge, and the traumatic memories themselves become a risk factor for later psychological problems. For family members watching from a bedside, seeing a loved one agitated, frightened, or speaking to people who are not there is alarming, especially when no one has explained that sepsis itself can do this to the brain.
How an Infection Outside the Brain Damages the Brain
The central puzzle is how an infection that might originate in the lungs, abdomen, or urinary tract ends up causing hallucinations and confusion. The answer involves several overlapping mechanisms, but they all share a common theme: the immune system’s response to infection spills over into the brain.
When the body detects an invading pathogen, immune cells release a flood of inflammatory signaling molecules. In a normal infection, this response is proportional and contained. In sepsis, the response spirals out of control. Those inflammatory molecules circulate through the bloodstream and eventually reach the blood-brain barrier, a tightly sealed layer of cells that normally keeps most blood-borne substances out of brain tissue. During sepsis, this barrier breaks down. The junctions between its cells loosen, inflammatory molecules cross into the brain, and immune cells from the bloodstream follow.3PubMed Central. Sepsis-Associated Encephalopathy and Blood-Brain Barrier Dysfunction The result is neuroinflammation on a scale the brain is not equipped to handle.
Once inflammation reaches the brain, the brain’s own immune cells, called microglia, activate. Under normal circumstances, microglia perform essential housekeeping: they trim unnecessary connections between neurons, clear debris, and patrol for threats. During sepsis, microglia shift into an aggressive inflammatory mode. Research on brain tissue from patients who died of sepsis has found evidence of excessive complement activation, a branch of the immune system, in the hippocampus, a region critical for memory and cognition. In animal models of sepsis, microglia tagged and destroyed synapses at a dramatically increased rate, stripping away the connections neurons need to function.4PubMed Central. Microglia mediate neurocognitive deficits by eliminating C1q-tagged synapses in sepsis-associated encephalopathy This synaptic destruction helps explain why sepsis can produce not just acute confusion and hallucinations but lasting cognitive damage.
The process starts at the periphery, but the signaling molecules that initiate neuroinflammation can enter the brain through multiple routes, including direct diffusion across damaged barrier cells and transport by specialized carrier proteins.5PubMed Central. Targeting the Blood-Brain Barrier to Prevent Sepsis-Associated Cognitive Impairment Astrocytes, the star-shaped support cells that help maintain the brain’s chemical environment, also become damaged and dysfunctional during sepsis, compounding the problem.6PubMed Central. Astroglia in Sepsis Associated Encephalopathy
Blood Flow and Chemical Imbalances in the Brain
Neuroinflammation is only one piece of the puzzle. Sepsis also disrupts the blood supply to the brain. In a healthy person, the brain has built-in mechanisms that keep blood flow steady even when blood pressure fluctuates. During sepsis, and especially in septic shock, this autoregulation can fail. A study measuring cerebral blood flow in sepsis patients found that while overall blood flow velocity and blood pressure were not reliably different between delirious and non-delirious patients, disturbed autoregulation was significantly associated with delirium.7PubMed Central. Cerebral perfusion in sepsis-associated delirium In other words, the problem is not necessarily that blood pressure drops but that the brain loses its ability to compensate when it does.
The damage to small blood vessels during sepsis compounds this effect. Endothelial cells lining the brain’s tiny capillaries become dysfunctional, microcirculation deteriorates, and the brain’s energy supply starts to fall behind its demands.8PubMed. Brain perfusion in sepsis When neurons do not get adequate oxygen and glucose, their signaling goes haywire. Neurotransmitter balance, the carefully regulated chemistry that allows neurons to communicate, becomes disrupted. These combined insults from inflammation, impaired blood flow, and neurotransmitter imbalance together create the conditions for delirium and hallucinations.9Journal of Intensive Care. A clinical perspective of sepsis-associated delirium
The Gut-Brain Connection
A newer line of research has uncovered an unexpected contributor to sepsis-related brain dysfunction: the gut. Sepsis dramatically alters the balance of bacteria in the intestines, and growing evidence points to this disruption as a driver of brain inflammation through what researchers call the gut-brain axis, the two-way communication network linking intestinal microbes to the central nervous system.10PubMed Central. Gut microbiota and sepsis-associated encephalopathy: pathogenesis and precision therapies
In animal models of sepsis, researchers have documented changes in gut structure, shifts in the diversity of gut bacteria, and altered levels of short-chain fatty acids, the metabolic byproducts that gut microbes produce and that influence brain function. The same animals showed increased inflammatory activity in brain tissue and went on to develop measurable cognitive decline.11PubMed Central. A crosstalk between gut and brain in sepsis-induced cognitive decline The communication runs through neural pathways like the vagus nerve, through immune signaling, and through hormonal channels. This research is still in its early stages, and no gut-targeted therapy for sepsis-associated brain dysfunction has been validated in humans. But it opens the door to the idea that what happens in the gut during sepsis may be actively making brain symptoms worse, not just tagging along as a bystander.
How Doctors Identify Sepsis-Related Brain Dysfunction
There is no single test that confirms a patient’s hallucinations or confusion are caused by sepsis rather than another condition. Diagnosis remains primarily clinical, based on bedside assessment tools that screen for delirium. Doctors look for fluctuating consciousness, inattention, disorganized thinking, and altered awareness. Because ICU patients often cannot speak due to breathing tubes or sedation, these assessments rely heavily on observable behavior. A valid biomarker that could definitively confirm the diagnosis and gauge its severity is still missing.12PubMed Central. Neurofilament light chains to assess sepsis-associated encephalopathy: Are we on the track toward clinical implementation?
That said, several laboratory and imaging tools are providing useful supplementary information. One blood marker, a protein called S100B that is released when brain cells are damaged, has shown promise. A meta-analysis found that patients with sepsis-associated encephalopathy had meaningfully higher S100B levels than sepsis patients without brain dysfunction, and that higher levels were associated with worse outcomes.13PubMed Central. Diagnostic and prognostic value of serum S100B in sepsis-associated encephalopathy: A systematic review and meta-analysis Tracking changes in S100B over the first few days of sepsis may be more informative than a single measurement. In one study, the level measured on day three was independently associated with brain dysfunction, while the day-one reading was not.14PubMed Central. The dynamic change of serum S100B levels from day 1 to day 3 is more associated with sepsis-associated encephalopathy Another marker under investigation, neurofilament light chain, reflects damage to the long fibers that connect neurons and may eventually serve as a way to predict long-term cognitive problems.12PubMed Central. Neurofilament light chains to assess sepsis-associated encephalopathy: Are we on the track toward clinical implementation?
Electroencephalography (EEG), which measures electrical activity in the brain, can also provide clues. EEG abnormalities are common during sepsis, with studies reporting background slowing or suppression in a wide range of patients. The presence of certain abnormal wave patterns has been linked to both the severity of encephalopathy and higher mortality.15PubMed Central. Clinical neurophysiological assessment of sepsis-associated brain dysfunction: a systematic review None of these tools are used in isolation to diagnose sepsis-associated hallucinations, but together they help clinicians build a picture of what is happening in the brain and how severe it is.
Why There Is No Quick Fix for Sepsis-Related Hallucinations
If you are hoping for a specific drug that targets sepsis-related hallucinations, the honest answer is that none exists. Because the hallucinations arise from the brain’s reaction to systemic infection rather than from a discrete psychiatric cause, the primary treatment strategy is to treat the sepsis itself. When the underlying infection is controlled and organ function stabilizes, the encephalopathy often resolves on its own. This pattern is consistent with the general behavior of metabolic encephalopathies: they tend to clear when the metabolic insult is corrected.
The role of sedation and certain ICU medications makes the picture more complicated. Many drugs used in critical care, including sedatives and painkillers, can themselves cause or worsen delirium. Clinicians walk a difficult line between keeping patients comfortable and avoiding medications that prolong confusion. A systematic review and meta-analysis examining non-pharmacological interventions for ICU delirium, such as structured sleep protocols, early mobilization, and reorientation strategies, found that current evidence does not support their effectiveness in reducing delirium incidence or duration in critically ill patients.16PubMed. The effectiveness of non-pharmacological interventions in reducing the incidence and duration of delirium in critically ill patients: a systematic review and meta-analysis That does not mean these strategies are useless in individual patients, but the data have not been strong enough to declare them clearly effective as a category.
This leaves clinicians relying on the basics: controlling the infection with appropriate antibiotics, supporting failing organs, minimizing unnecessary sedation, and monitoring brain function as closely as possible. The frustrating reality is that the brain injury during sepsis often outpaces the available tools to prevent it.
What Happens to the Brain After Sepsis Resolves
Perhaps the most underappreciated aspect of sepsis-related hallucinations and delirium is what comes after. Surviving sepsis does not mean the brain bounces back to its previous state. More than half of sepsis survivors experience severe, long-lasting cognitive problems that affect their daily lives and impose a significant burden on caregivers.17PubMed Central. Sepsis-Associated Encephalopathy: From Delirium to Dementia? These deficits can include trouble with memory, attention, planning, and processing speed, changes that persist for months or years.
Brain imaging studies have revealed structural damage in sepsis survivors. MRI scans of patients who developed brain dysfunction during sepsis have shown white matter lesions and, in some cases, ischemic strokes. White matter damage, sometimes called leukoencephalopathy, was associated with a blood-clotting problem called disseminated intravascular coagulation and with higher mortality.18PubMed Central. Pattern of brain injury in the acute setting of human septic shock Separate research measuring brain volume found that sepsis-related brain dysfunction was associated with shrinkage in multiple regions, including the cerebral and cerebellar white matter, the cortex, the hippocampus, and the amygdala.19PubMed. Brain Volume Changes in Patients with Acute Brain Dysfunction Due to Sepsis These are not subtle or ambiguous findings. They represent measurable tissue loss in brain areas essential for memory, emotion, and coordinated thought.
Unfortunately, no targeted treatment currently addresses the underlying mechanisms of this cognitive damage. Brain imaging can detect changes, but clinicians have limited tools to reverse them.20PubMed Central. Sepsis-associated brain injury: underlying mechanisms and potential therapeutic strategies for acute and long-term cognitive impairments Rehabilitation after sepsis focuses on physical recovery, occupational therapy, and cognitive exercises, but the evidence base for these approaches specifically in sepsis survivors remains thin.
Psychiatric Fallout Beyond Cognition
The long-term aftermath of sepsis is not limited to memory and thinking problems. Anxiety, depression, and post-traumatic stress disorder are common among survivors, a cluster sometimes grouped under the term “post-sepsis syndrome.”21PubMed Central. Post-sepsis syndrome – an evolving entity that afflicts survivors of sepsis These psychiatric conditions are themselves associated with increased long-term mortality in sepsis survivors, making them far more than a quality-of-life concern.22PubMed Central. Post-sepsis psychiatric disorder: Pathophysiology, prevention, and treatment
The risk factors for developing psychiatric problems after sepsis include several that are potentially modifiable: the number of traumatic memories a patient retains from the ICU stay, the length of time spent in intensive care, and the use of certain medications like vasopressors and inotropes.22PubMed Central. Post-sepsis psychiatric disorder: Pathophysiology, prevention, and treatment The fact that traumatic ICU memories are a risk factor circles back to hallucinations in an important way. A patient who hallucinates terrifying scenes during sepsis and later remembers those scenes vividly is carrying a psychological burden that extends well beyond the hospital stay. This makes the in-hospital experience matter even after the infection clears.
For families, the practical takeaway is that a loved one who survived sepsis and seemed physically recovered may still be struggling with invisible cognitive and emotional injuries. These problems can emerge weeks or months later and are easily mistaken for depression, aging, or personality changes rather than being recognized as consequences of the sepsis itself. Neurological impairment from sepsis-associated delirium can persist for months or longer after the initial episode, impairing rehabilitation potential in ways that catch patients and families off guard.23PubMed Central. Sepsis Associated Delirium Knowing that these outcomes are common and have a biological basis, not a personal failing, can be the first step toward getting appropriate follow-up care.