Anosmia — Loss of the Sense of Smell

What Is Anosmia?

Anosmia is the medical term for the complete loss of the sense of smell. It can occur on its own or alongside loss of taste — most of what we think of as "taste" is actually delivered by the olfactory nerves at the top of the nose, which is why food becomes bland in patients with anosmia. The most common causes are:

• Post-viral anosmia — most prominently after COVID-19, but also after other respiratory viruses. Many patients recover spontaneously over months; some have persistent loss.
• Chronic sinus disease and nasal polyps — see Sinusitis. Often partially or fully reversible with steroid sprays and surgery.
• Head injury — particularly shearing injury to the small olfactory nerve fibres at the top of the nose.
• Neurodegenerative disease — Parkinson's disease and Alzheimer's disease can both reduce smell, sometimes years before other symptoms become apparent.
• Medication side-effects, chemotherapy, radiotherapy, and certain occupational exposures.
• Rare structural causes — tumours in the front of the brain, which is why persistent unexplained anosmia warrants a specialist opinion and sometimes an MRI scan.

Staying Safe With Anosmia

The first thing to address with any patient who has lost their sense of smell is safety. There are several specific risks worth knowing about.

Household gas

The greatest immediate danger of anosmia is the inability to detect a gas leak at home. Natural gas is flammable and poisonous; the smell added to it (mercaptan) is what alerts most people to a leak. With anosmia, that warning is absent.

• Have your gas appliances serviced every year by a Gas Safe registered engineer.
• Install a natural gas detector at home. Your local fire service can advise on suitable models and placement.
• If you suspect a gas leak (for example, friends or family report smelling gas, or you notice anything unusual about your appliances), call the National Gas Emergency Service on 0800 111 999 immediately.
• Consider also installing a carbon monoxide alarm — carbon monoxide is odourless to everyone, but anosmia removes the protective effect of smelling associated combustion gases.

Food

• Not being able to identify food that has gone off is a real risk. Pay close attention to "use-by" dates — they exist to keep you safe.
• Where possible, ask a friend or family member to smell food for you, especially meat, fish, dairy, and leftovers.
• If you are not sure, discard the food. Replacing a meal is cheap; food poisoning is not.
• Anosmia sufferers often lose the joy of eating, which can lead to weight loss and malnutrition. Maintaining a healthy, balanced and varied diet is important. Use ingredients that stimulate the remaining taste senses — salty, bitter, sweet, sour — and use spices to add interest. Experiment with combinations of texture and colour. Some patients find this also helps olfactory recovery (see below).

Personal hygiene

Body odour is something we usually monitor through smell. With anosmia, it is easy to be unaware of unintentional body odour or clothing odour. Maintain a consistent personal hygiene routine — regular washing, daily deodorant, regular laundry — by clock rather than by perception.

Olfactory Training

Olfactory training is a safe, simple, evidence-based intervention that may help recovery of the sense of smell, particularly after post-viral anosmia. It works by repeatedly stimulating the olfactory pathways with structured exposure to a small range of recognisable smells. There is good research behind this approach. The protocol below is the one used in published studies, also recommended by the 5th Sense charity.

What you need

• Four essential oils — lemon, rose, clove, and eucalyptus. Available online or from health food shops.
• Four small glass jars with lids — OR cotton pads — OR fragrance strips. The jar method is what was used in the original studies; the physics is that an enclosed air space above the liquid allows odour vapour to build up, increasing the available concentration. Cotton pads or fragrance strips also work fine.

How to do it

1. If using pads or strips: pour a few drops of one of the oils onto the testing stick or pad.
2. Wait a few minutes for the fragrance to develop. Do not sniff immediately.
3. Hold the first jar, pad, or strip about an inch from your nose. The order of smells does not matter.
4. Relax and inhale naturally through the nose. Sniffing too quickly or deeply tends to result in detecting nothing.
5. Try this two or three times, then rest for five minutes.
6. Move on to the next smell and repeat.

Tips

• Train at least twice every day — ideally morning and evening.
• Relax and inhale naturally — about 10 seconds per smell is enough.
• Try smelling other things between formal training — spices in the cupboard, flowers in the garden, fragrances. Anything safe to smell.
• Stick with it. Some people detect something within a couple of weeks; some take much longer; some do not benefit. Everyone is different. Do not be disheartened if there is no immediate improvement.
• The training is most effective if continued for at least 3 months, and many published studies follow patients training for 6–12 months.

When to See a Specialist

See an ENT surgeon for assessment if any of the following apply:

• Sudden onset of anosmia without an obvious viral illness.
• Anosmia associated with nasal blockage, polyps, or chronic sinus disease — see Sinusitis and FESS & Polypectomy Consent.
• Anosmia after head injury.
• One-sided anosmia (smelling normally on one side but not the other).
• Persistent anosmia more than six months after a viral illness, particularly if accompanied by parosmia (distorted smells, often unpleasant).
• Anosmia accompanied by neurological symptoms — headache, memory problems, tremor, or changes in personality — needs urgent investigation.

Booking and Next Steps

If you would like to discuss anosmia in a clinical setting, the secretarial team can arrange a consultation. See also Blocked Nose, Sinusitis, and Hay Fever & Allergic Rhinitis.