Phantosmia

Key takeaways

Phantosmia belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phantosmia to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phantosmia from memory before moving on to harder problems.

Reference excerpt

Phantosmia (phantom smell), also called an olfactory hallucination or a phantom odor, is smelling an odor that is not actually there. It can occur in one nostril or both. Unpleasant phantosmia, also called cacosmia, is more common and is often described as smelling something that is burned, foul, spoiled, or rotten. Experiencing occasional phantom smells is normal and usually goes away on its own in time. When hallucinations of this type do not improve on their own or when they keep coming back, it can be very upsetting and can disrupt an individual's quality of life. Olfactory hallucinations can be caused by common medical conditions such as nasal infections, nasal polyps, or dental problems. It can result from neurological conditions such as migraines, head injuries, strokes, Parkinson's disease, seizures, or brain tumors. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication or withdrawal from drugs and alcohol, or psychotic disorders. Environmental exposures are sometimes the cause as well, such as tobacco smoke, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer. A physician can determine if the problem is with the sense of smell (olfactory system) or taste (gustatory system), or if it is caused by a neurological or psychiatric disorder. Phantosmia usually goes away on its own though this can sometimes be gradual and occur over several years. When caused by an illness (e.g., sinusitis), it should go away when the illness resolves. If the problem persists or causes significant discomfort, a doctor might recommend nasal saline drops, antidepressant or anticonvulsant medications, local anesthesia to parts of the nose, or in very rare circumstances, surgical procedures to remove the olfactory nerves or bulbs.

Symptoms Other olfactory disorders such as hyposmia and anosmia have been found to be a symptom of mood disorders (depression). However, it is not known what olfactory disorders occur and if they are indeed a symptom of a depressive disorder. It has been proposed that phantosmia may be an early sign of the neurodegenerative disease Parkinson's disease. It may also be a sign of an intracranial hemorrhage (brain tumours or epilepsy). Other studies have also found that the symptoms of phantosmia have been alleviated after the patient has been treated for depression. Another case of a 70-year-old male reported that his first abnormal symptoms were irregular bowel movements. After this the patient developed irregular eye movements and had developed a sleep and behavior disorder. He subsequently developed phantosmia, in which what he smelled was described as "stinky and unpleasant". The patient did not display any of the following symptoms: loss of awareness; confusion; automatisms; convulsive seizures; auditory/visual hallucinations.

Co-occurrence with other conditions Phantosmia has been found to co-exist in patients with other disorders such as schizophrenia, epilepsy, alcoholic psychosis, and depression. It has also been found that many patients may begin to experience depression after the occurrence of phantosmia and have looked towards committing suicide. The occurrence of depression resulted from the severe symptoms of phantosmia as everything even food smelled spoilt, rotten and burnt for these patients. By the age of 80, 80% of individuals develop an olfactory disorder. As well 50% of these individuals also have anosmia.

Migraines In 2011 Coleman, Grosberg and Robbins did a case study on patients with olfactory hallucinations and other primary headache disorders. In their 30-month long study, the prevalence rates for phantosmia turned out to be as low as 0.66%. In their findings, it was observed that a typical hallucination period was of 5–60 minutes, occurred either before or with the onset of head pain, and typically consisted of an unpleasant odor. It was also noted that phantosmia occurs most commonly among women having a migraine complaint. In their study, prophylactic therapy for headaches helped cure phantosmia in most of the patients. This finding is consistent with the findings of Schreiber and Calvert in 1986 which also mentioned the olfactory hallucinations before the occurrence of a migraine attack in four of their subjects.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Phantosmia

Start with the simplest possible case. Write down what Phantosmia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phantosmia before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phantosmia ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phantosmia

In research: Phantosmia appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phantosmia in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phantosmia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hallucinations, Neurological disorders, Olfactory system, so understanding it makes those chapters shorter.
In everyday life: Look for Phantosmia outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Phantosmia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phantosmia means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phantosmia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phantosmia in simple terms?

Phantosmia (phantom smell), also called an olfactory hallucination or a phantom odor, is smelling an odor that is not actually there. It can occur in one nostril or both.

Why does Phantosmia matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phantosmia?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phantosmia.