Anosmia (Loss of Sense of Smell) Causes and Treatment

What is Anosmia?

Anosmia Definition

Anosmia is the medical term for a complete loss of the sense of smell (olfaction). It can be temporary or permanent and while taste may not be affected, it does impact on the perception of flavors.

If the sense of smell is reduced (partial, not complete loss) , then this is known as hyposmia.

Other olfactory phenomenon include :

  • Parosmia which is the sensation of smell despite the absence of appropriate stimuli.
  • Dysosmia which is when the sense of smell is distorted.
  • Cacosmia which is the sensation of a bad smell or foul odor.

Olfactory Anatomy and Physiology

The olfactory epithelium is z small layer on the roof of he nasal activity that is responsible for the sense of smell. The olfactory receptor cells which make up the olfactory epithelium are neurons (nerve cells) that  transmits impulses to the brain where it is perceived as an odor.

There are two other types of olfactory cells apart from the receptor cells. Firstly, the supporting cells as the name suggests supports the neighboring receptor cells and helps ‘trap’ chemicals with their microvilli. Secondly, the basal cells which are immature or stem cells that can differentiate into olfactory receptor cells or supporting cells. It is important to note that the olfactory neuroepithelium is one of the only neural tissue in the body that can regenerate.

Another important component to take note of is the Bowman’s gland which secretes fluids that bathe the olfactory epithelium. This allows airborne chemicals to dissolve in the serous fluid and stimulate the receptor cells.

Olfactory receptor fibers bundle to join at the olfactory bulb which in turn leads to the olfactory nerve (cranial nerve CNI). This enters the brain at the olfactory center (part of the pyriform cortex) with nerve fibers to the thalamus, amygdala and enterorhinal area. Simply this means that apart from the perception of smell, the other areas may play a part in memories associated with odors which could trigger certain emotions and behavior.

Causes Anosmia

The causes can be divided according to disturbances in olfactory physiology :

  1. Any obstruction of air intake through the nose or in making contact with the olfactory epithelium.
  2. Damage of the olfactory epithelium.
  3. Damage of the pathways that transmits the sensory impulses from the olfactory receptor cells to the brain.

Nasal Obstruction

  • Any cause of nasal congestion will restrict air flow through the nose.
  • Nasal polyps.
  • Nasal bone deformities, deviated septum.
  • Foreign body in the nasal passages which may occur in children.
  • Tumors.

Patients with a tracheostomy will also experience anosmia since air intake is not through the nasal passages.

Damage of the Olfactory Epithelium

  • Chronic rhinitis – allergic (like hay fever) or non-allergic.
  • Sinusitis – acute or chronic
  • Viral infections of the upper respiratory tract like the common cold, seasonal flu (influenza).
  • Tumors may also cause damage of the olfactory epithelium.
  • Smoking – tobacco, marijuana, narcotic drugs.
  • Environmental or occupational hazard from constant smoke and toxic gas inhalation.
  • Chemical toxins including chlorine, sulfuric acid, formaldehyde, cadmium, manganese, lead and other hazardous substances. Excessive or prolonged use of nasal decongestants can also damage the epithelium.
  • Drug side effects including psychotropic drugs, hormones and corticosteroids. Radiation therapy may also result in damage of the olfactory epithelium.
  • Age related changes.

Damage of the Nerve Pathway(s)

While the olfactory epithelium, including the receptor cells can regenerate to some extent from differentiation of the basal cells, other neural tissue cannot if there is cell death. However not all cases of nerve damage resulting in anosmia is permanent as sometimes there is temporary irritation along the nerve pathway which will ease upon removing the causative factor.

Some of the causes which affects the transmission of sensory impulses to the brain and/or processing of these impulses includes :

  • Age related changes.
  • Chemical toxins like lead and certain insecticides.
  • Head injury.
  • Infection of the central nervous system like meningitis, encephalitis.
  • Brain or nerve tumors.
  • Intracranial surgery.
  • Any disease resulting in nerve or nerve sheath degeneration, nerve atrophy, inflammation or death or neurotransmitter dysfunction can result in anosmia like Parkinson’s disease, diabetic neuropathy, Alzheimer’s, stroke (CVA) and other related conditions.

If the anosmia is of a sudden onset and/or presents along with other neurological symptoms, immediate medical attention is required, especially if there is a history of head trauma.

Treatment of Anosmia

Treatment should be directed at the cause once it is identified. This may require further investigative tests like a CT scan or MRI of the head. The most common causes of anosmia include sinusitis, rhinitis, upper respiratory tract infections, drug side effects, smoking and age related changes, particularly in Alzheimer’s patients.

  • Rhinitis may require antihistamines and corticosteroids and nasal decongestants should be limited due to possible side effects.
  • Surgery may be necessary to correct bone deformities or remove obstructions. This includes a sinus drainage.
  • Chronic drugs should be changed to verify whether the sense of smell returns.
  • Smoker’s should be made aware that the condition will persist as long as they continue smoking.

Please note that any information or feedback on this website is not intended to replace a consultation with a health care professional and will not constitute a medical diagnosis. By using this website and the comment service you agree to abide by the comment terms and conditions as outlined on this page

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  • jPalm

    are there sensors (portable)to wear to fore warn me of excessive vapors, Co2,
    gas, thinners, all harmful gasses.
    I have had to many people tell me to get out of the room or car I am in because of strong bad harmful gases. something to mount on my dash for gas leaks, etc.
    I have found nothing to aid in advance notice of dangerous gases/ Please advise

  • Dr. Chris

    Hi JPalm

    To be honest, I am not aware of such devices for a anosmia. But there are gas detectors that are available commercially. Either way, some of these gases would not be detectable by the sense of smell in a person with no impairment. If you are exposed to such conditions then you should be using a gas detector. Cannot advise on these devices but you should speak to an ENT specialist (otolaryngologist) about such a device.

  • shashi prakash

    sir i have completely lost my sense of smell past 8 yrs. i was suffering from sinus (frequent cold like situation)for 4 to 5 years. got treated for nearly 1 year, no benefit instead i lost my smell sense completly.Then consulted in BHU , they told its ELERGIC RHINITIS got treated for it. now i don’t get frequent cold. what should i do now to gain back my smell sense?

  • Dr. Chris

    Hi Shashi Prakash

    You need to see an otolaryngologist (ENT specialist) who will be able to assess your case and tell you if this is permanent or temporary. Even though you are asymptomatic now, the medication you are using may also be disrupting your sense of smell (possibly). Speak to your doctor.

  • Marrit Oost (NL)

    Hello,

    I have no memory of having a sense of smell. When I was 11 years old I found out. We went to a couple of doctors but nobody really knew what they were talking about. I am now 21 therefore seeking more information. As far as I know I am born with anosmia, is there anything I can do now? Is there a point for me going to see my GP these days about my anosmia?

    I hope you can help me and I hope that more will be known about treating anosmia!

    Kind Regards,

    Marrit

  • Dr. Chris

    Hi Marrit

    If it is a congenital defect (present since birth), then depending on the cause. there may be very little that can be done at this point. You should nevertheless consult with an ENT specialist (ear-nose-throat / otolaryngologist), especially if you know of one in your area who specializing in olfactory disorders. Your GP may be able to refer you to a suitable practitioner.

  • Kim Sears

    I have had severe sinus problems ie: hayfever, airborne issues most of my life. For many years I dealt with being stuffed up constantly, I ended up addicted to Dristan nose spray for 13 yrs. I was given a surgery to coterize my nose in order to get me off the spray and have not used it since. That was about 22 yrs ago. After that I really didn’t suffer with a stuffed up nose, only a runny nose. I still was able to smell. Now I still suffer with hay fever but only have a runny nose during that season. I lost my ability to smell about 4 years ago. I have had polyps removed twice in my life. I was told that I likely would never be able to smell again. This was heart breaking to me. I was recently put on prednisone by an ENT, to see if inflammation was the cause of my in ability to smell or possible damage from the two surgeries I had in the past. Within a few hours of taking my first dose I was partially smelling again. I knew then that inflammation was probably my issue, however was told I could not stay on that medication long term because it can be dangerous. After discontinuing the medication I could no longer smell again. Recently I had cut out drinking milk something I did excessively all my life, and all of a sudden I had the ability to smell again partially. Only sweeter smells. I have come to conclusion that milk was causing me this problem. If I drink even a small amount of milk It’s gone again for a week or so. I ate something that had a milk product in it the other day and again lost the ability. I am wondering if this even makes sense as I have no other physical ailments when I drink milk, and my dr said he has never heard of milk only affecting that one thing before. Can milk proteins do this?

  • Ann ArkKey

    I lost my sense of smell after a severe head trauma. Multiple skull fractures and eventually my brain herniated through one of the fractures. I was wondering if there is now 30 years later any help as far as nerve regeneration to repair the olfactory nerve?