Seizures are complex neurological events resulting from abnormal electrical activity in the brain. While primary manifestations often involve motor symptoms or altered consciousness, a common question arises regarding sensory experiences, particularly whether seizures possess a distinct odor. The relationship between seizures and smell is nuanced, encompassing both subjective perceptions by the individual and external odors that may arise as secondary effects.
The Nuance of Seizure Odors
Seizures themselves do not inherently produce a unique, identifiable smell. The electrical discharges in the brain that define a seizure do not emanate an odor detectable by others. Any perceived smells are typically not a direct byproduct of the seizure activity. Instead, these olfactory associations are usually secondary phenomena, originating either within the individual’s brain as a sensory hallucination or from external factors related to the seizure event. While smell can be a component of the seizure experience, it does not mean the seizure itself is releasing an odor into the environment.
Olfactory Auras
Olfactory auras represent a specific type of sensory hallucination experienced by an individual as part of a focal aware seizure or as a warning sign preceding a larger seizure. These auras are subjective, meaning only the person experiencing the seizure perceives the smell, which is not detectable by others in the vicinity. The smells associated with these auras are often described as unpleasant, such as burning rubber, rotten eggs, metallic, or chemical odors. Some individuals might also perceive unusual but not necessarily unpleasant smells, like a strong floral scent or even food-related odors like roast beef or baked brownies.
These phantom smells arise from abnormal electrical activity in brain regions responsible for smell perception, primarily within the temporal lobe, especially the mesial temporal structures like the amygdala and piriform cortex. The brain generates a perception of smell without external stimulus when these areas are affected by seizure discharge. Olfactory auras can serve as an early warning sign, sometimes lasting from seconds to an hour before the seizure progresses. While relatively uncommon, occurring in about 5.5% to 13% of patients with temporal lobe epilepsy, their consistent and often stereotyped nature can be a helpful indicator of an impending seizure.
External Factors Creating Perceived Smells
While internal olfactory auras are subjective, observers might perceive smells during or after a seizure due to various external factors. These odors are not directly from the seizure itself but are consequences of physical events that can occur during a seizure. For instance, loss of bladder or bowel control, incontinence, can lead to the smell of urine or feces. This is a common occurrence during certain types of seizures, particularly tonic-clonic seizures.
Vomiting can also occur during or after a seizure, especially if the seizure activity affects areas of the brain involved in nausea and emesis, such as those in the temporal lobe. The smell of vomit would then be present. Accidental injury during a seizure, such as falling onto a heat source, could result in a burning smell, like singed hair or skin. This results directly from physical injury.
Less commonly, metabolic changes can contribute to noticeable breath odors. For example, individuals on a ketogenic diet, sometimes used to manage seizures, might produce ketones that cause a distinct, often fruity or sweet, breath odor. This “keto breath” is a sign of ketosis and is not directly caused by the seizure itself, but rather by the body’s metabolic state. Environmental factors, such as the person having been near something with a strong smell before the seizure, could also be mistakenly attributed to the seizure event.