An elevated body temperature resulting from an infection or illness can sometimes be accompanied by surprising cognitive changes. Hallucinations involve perceiving something that is not actually present. A fever can definitively cause these perceptual alterations, which are temporary changes in consciousness or perception. These changes, while frightening, are a known side effect of the body’s inflammatory response to illness.
The Reality of Fever-Induced Altered States
The temporary cognitive and behavioral changes associated with high temperatures are often classified as “febrile delirium” or “febrile confusion.” This state is characterized by acute confusion and a fluctuating level of consciousness that develops rapidly, typically over a few hours or days. Delirium is usually a transient condition, meaning it is not a sign of permanent brain damage, and generally resolves as soon as the fever subsides and the underlying illness is treated.
Certain populations are more susceptible to experiencing delirium when their temperature rises. Young children and older adults are particularly vulnerable, as are individuals with pre-existing neurological conditions or cognitive impairment like dementia. While hallucinations can occur with any fever, they are more commonly associated with high-grade fevers, often around 102°F (38.9°C) or higher. In children, fever-induced delirium often occurs at night and is typically very brief.
How High Temperatures Affect Brain Chemistry
The connection between fever and altered perception begins with the body’s inflammatory response to infection. When the immune system detects a threat, it releases signaling molecules called cytokines, such as Interleukin-1 (IL-1) and Interleukin-6 (IL-6), into the bloodstream. These inflammatory mediators signal the brain, specifically the hypothalamus, to raise the body’s temperature set point, thus causing the fever.
Cytokines communicate with the brain in several ways, including stimulating nerve pathways and inducing the synthesis of prostaglandin E2 (PGE2) in the brain’s blood vessels. PGE2 then acts on the temperature-regulating center in the hypothalamus. Furthermore, some cytokines can directly cross the blood-brain barrier or activate receptors on the barrier’s surface. This process of neuroinflammation disrupts normal brain function by interfering with neurotransmitter systems, such as the serotonin and dopamine pathways, which regulate mood, sleep, and perception.
The increased temperature itself also stresses neuronal tissue, demanding more metabolic resources. When the brain is under this combined chemical and thermal stress, its normal processing of sensory information becomes impaired, which manifests as confusion and hallucinations. Dehydration, a common side effect of fever, can further contribute to this neuronal stress and imbalance, exacerbating the symptoms of delirium.
Recognizing the Signs of Febrile Hallucinations
Febrile hallucinations, or delirium, present as a sudden and noticeable change in a person’s mental state and behavior. The hallucinations can involve any of the senses, but are most frequently visual or auditory. Visual hallucinations often involve seeing objects, shapes, or figures that are not present, such as shadows or distorted room features. Auditory hallucinations may be reported as hearing loud sounds, voices, or music. The person experiencing delirium may also display agitation, restlessness, emotional lability, or confusion about their location and the time of day. These symptoms are usually brief and transient, resolving quickly as the fever is brought down or the underlying illness improves.
When to Consult a Healthcare Provider
While fever-related hallucinations are often temporary and harmless, they can occasionally signal a more serious underlying condition that requires immediate medical attention. Initial management involves supporting the person by ensuring they are hydrated and using over-the-counter antipyretics, like acetaminophen or ibuprofen, to lower the body temperature. Creating a calm and reassuring environment can also help reduce distress during the episode of confusion.
There are several “red flag” symptoms that indicate the need for prompt evaluation by a healthcare provider. These include:
- Confusion or delirium that persists long after the fever has subsided.
- A fever that lasts longer than three days.
- A severe headache, sensitivity to light, or a painful or stiff neck.
- Difficulty waking up or having a seizure.
These symptoms can be signs of serious infections, such as meningitis or encephalitis, which require urgent diagnosis and treatment.