Decreased Ability To Smell

What Causes Reduced Sense Of Smell?

Reduced sense of smell can have various causes, ranging in severity from 'worrying' to 'generally fatal'.  Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.

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Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms.  In order to diagnose reduced sense of smell, we could:

  • Research the topic
  • Find a doctor with the time
  • Use a diagnostic computer system.
The process is the same, whichever method is used.

Step 1: List all Possible Causes

We begin by identifying the disease conditions which have "reduced sense of smell" as a symptom.  Here are eight of many possibilities (more below):
  • Nasal Polyps
  • Sarcoidosis
  • Schizophrenia
  • Brain Tumor
  • Megaloblastic Anemia
  • Hypothyroidism
  • General Toxicity
  • Cigarette Smoke Damage

Step 2: Build a Symptom Checklist

We then identify all possible symptoms and risk factors of each possible cause, and check the ones that apply:
poor cold weather tolerance
frequent rashes
elevated TSH
having trouble concentrating
swollen cervical nodes
frequent unexplained sadness/crying
constant fatigue
minor swelling at front of neck
T3-T4 thyroid hormone use
hyperthyroidism in family members
acute bronchitis
having non-scalp scaly/flaky skin
... and more than 80 others

Step 3: Rule Out or Confirm each Possible Cause

A differential diagnosis of your symptoms and risk factors finds the likely cause of reduced sense of smell:
Cause Probability Status
Schizophrenia 98% Confirm
Hypothyroidism 30% Unlikely
Nasal Polyps 19% Unlikely
Cigarette Smoke Damage 0% Ruled out
Megaloblastic Anemia 0% Ruled out
Sarcoidosis 0% Ruled out
General Toxicity 0% Ruled out
Brain Tumor 0% Ruled out
* This is a simple example to illustrate the process

Arriving at a Correct Diagnosis

The Analyst™ is our online diagnosis tool that learns all about you through a straightforward process of multi-level questioning, providing diagnosis at the end.

In the Nose/Smell Symptoms section of the questionnaire, The Analyst™ will ask the following question about decreased ability to smell:
Has your sense of smell declined within the past few years, for reasons other than nasal congestion?
Possible responses:
→ Don't know
→ No, my sense of smell has remained about the same
→ Yes, but it is due to ongoing nasal congestion
→ Yes, it is somewhat worse now
→ Yes, it is a lot worse now
Based on your response to this question, which may indicate no change in sense of smell, loss of smell due to blocked nose, reduced sense of smell or much reduced sense of smell, The Analyst™ will consider possibilities such as:
Alzheimer's Disease

Reduction of the sense of smell has been identified as an early sign of Alzheimer's disease since the 1970s.

Brain Tumor

Specifically, tumors of the frontal lobe.

Cocaine Addiction

Intranasal drug use can cause a loss of the sense of smell.

General Detoxification Requirement

Toxins – especially acrylates, methacrylates and cadmium – can cause a reduction in the sense of smell.


[Kieff, D; Boey, H; Schaefer, P; Goodman, M; Joseph, M (1997).  "Isolated neurosarcoidosis presenting as anosmia and visual changes".  Otolaryngology – Head and Neck Surgery 117 (6): pp183-6]


[Rupp, Claudia I.; Fleischhacker, W.  Wolfgang; Kemmler, Georg; Kremser, Christian; Bilder, Robert M.; Mechtcheriakov, Sergei; Szeszko, Philip R.; Walch, Thomas et al (2005).  "Olfactory functions and volumetric measures of orbitofrontal and limbic regions in schizophrenia".  Schizophrenia Research 74 (2-3): pp149-61]

Zinc Requirement

Zinc deficiency is rare in the developed world, but it can cause impaired sense of smell or taste.

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