Short answer
A reduced sense of smell is called hyposmia. Colds, nasal or sinus problems, infections, age, medication, head trauma and other conditions can play a role. When the loss is sudden, severe, long-lasting or unexplained, it is best to have it assessed medically.
First: is it temporary or striking?
With a blocked nose during a cold, temporarily smelling less is not unusual. But when, without obvious nasal congestion, you suddenly barely smell coffee, perfume, smoke or food, that deserves attention.
The NIDCD distinguishes, among others, hyposmia (reduced smell), anosmia (no smell), parosmia (distorted smells) and phantosmia (perceiving a smell that is not there).
Think about safety too
Smell warns of smoke, gas-like odours and spoiled food. With clear loss of smell, it is wise to rely on properly working smoke detectors and other relevant safety detectors and to pay extra attention to expiry dates and food safety.
When to see a doctor?
Contact a GP or ENT specialist when the loss of smell is sudden without a clear explanation, occurs after head trauma, persists, clearly worsens or is accompanied by other neurological or serious symptoms.
A doctor can assess the nose and sinuses, review medication and medical history and, if necessary, carry out a standardised smell test or refer you.
Can smell training help?
Olfactory training is a simple method in which different scents are smelled repeatedly and attentively over weeks to months. Studies and reviews find improvement in certain groups, but results vary depending on the cause and duration of the smell disorder.
So use smell training as a possible rehabilitation strategy, not as a substitute for diagnosis.
Avoid untested "miracle cures"
Online, supplements, essential oils and other treatments are offered as a quick fix. However, loss of smell has various causes and therefore various treatments. What makes sense for one cause can be pointless for another.
Smell is also quality of life
Smelling less can affect eating, safety, social experience and enjoyment. It is therefore a real health problem and not a trivial inconvenience.