The perception of an odor when no physical source is present is known as phantosmia, or an olfactory hallucination. This phantom scent is often described as a chemical smell, frequently reported as the distinct odor of rubbing alcohol or acetone. This experience signals a false or distorted signal within the complex system responsible for our sense of smell. Causes range from simple environmental factors to internal or neurological issues, and the specific smell of acetone often points toward a known metabolic byproduct.
Transient Environmental Factors
Sometimes, the phantom smell is not a hallucination but a lingering perception from a recent, intense exposure. If you were recently using cleaning products, paints, or solvents, the chemical molecules can temporarily saturate the olfactory receptors in your nose. This can lead to a brief period of olfactory fatigue, where the receptors are overwhelmed and continue to fire signals after the source has been removed.
The persistent smell might also be due to residual vapors trapped in clothing, hair, or the immediate environment, such as a freshly cleaned room. Low humidity and severe nasal dryness can also make the sensitive nasal lining more susceptible to irritation and distorted odor perception. These environmental factors are usually self-correcting, with the smell fading shortly after moving to a fresh environment.
Internal Body Chemistry and Acetone Production
The smell of rubbing alcohol is chemically similar to acetone, a type of ketone body. The body naturally produces ketones as a byproduct when it burns fat for fuel instead of glucose, a metabolic state known as ketosis. Because acetone is volatile, the body excretes it through the breath, leading to a distinct, often sweet or chemical, odor.
Ketosis is a common state for people following very low-carbohydrate or ketogenic diets, or during periods of prolonged fasting. In these instances, the acetone smell is a benign sign that the body has successfully shifted its primary energy source from carbohydrates to fat. However, high ketones and the resulting acetone smell can also signal a potentially dangerous medical condition known as diabetic ketoacidosis (DKA).
DKA occurs when there is a lack of insulin, causing blood sugar and ketone levels to rise dangerously high, making the blood overly acidic. Unlike nutritional ketosis, DKA is a medical emergency, most commonly affecting individuals with type 1 diabetes. If the acetone smell is accompanied by symptoms like excessive thirst, frequent urination, nausea, vomiting, confusion, or rapid, deep breathing, immediate medical attention is necessary.
Issues within the Nasal Passages and Olfactory System
The origin of a phantom smell is often a structural or inflammatory problem in the peripheral olfactory system, which includes the nose and its nerves. Chronic sinusitis, an inflammation of the sinus cavities, can trap odor-producing bacteria or distort the signals sent by the olfactory nerves. This inflammation can cause sensory nerves to misfire, generating a false chemical smell signal.
The presence of nasal polyps, which are non-cancerous growths, can similarly interfere with normal airflow and olfactory signaling. Damage to the olfactory neurons following a severe upper respiratory infection, such as a cold, flu, or COVID-19, is also a frequent cause of phantosmia. This post-infectious dysfunction causes damaged nerves to send errant signals to the brain, which are interpreted as a strong chemical odor.
When Phantom Smells Signal a Neurological Concern
A persistent or sudden phantom smell can sometimes originate from the central nervous system, indicating a neurological event. The brain’s temporal lobe is heavily involved in processing smells, and abnormal electrical activity here can trigger an olfactory hallucination. This is known as an olfactory aura and can be a precursor to certain types of epileptic seizures, particularly temporal lobe seizures.
These neurological phantom smells are often sudden in onset and may be brief, lasting only seconds or minutes. Rarely, a brain tumor or a lesion near the olfactory bulb or temporal lobe can press on the neural tissue responsible for smell. If the phantom smell is accompanied by symptoms such as unsteadiness, unprovoked memory loss, visual changes, or a seizure, consulting a physician immediately is mandatory to rule out a serious underlying condition.