Around three million people in the UK are not able to smell, and that can have serious side effects leading to isolation and depression.
It's caused by an illness or infection and can happen very suddenly.
Now, help is at hand from a Hampshire charity training people to smell again.
Watch this report by Mary Stanley:
Sophie Martyn first noticed a loss of smell after having a common cold five years ago, but it didn't come back.
Sophie Martyn, lost sense of smell
Side effects of smell loss:
Can trigger anxiety, isolation and depression
Dangers from fire and food that has gone off
Loss of taste- so food loses it's enjoyment
Emotions, memories and moos are linked to smell
Smell loss can be present from birth but is more likely to be caused by an illness or infection, a blow to the head, a result of cancer treatment or side effect of medication or part of the ageing process.
However, there is hope!
Chrissi Kelly lost her sense of smell after a sinus infection 8 years ago. From her home in Chilbolton in Hampshire, she now runs smell training courses which she describes as physiotherapy for the nose.
It involves smelling essential oils twice a day, retraining the brain and stimulating the olfactory nerve to regenerate.
It's also a chance for people to meet others facing the same loss
Chrissie Kelly, AbScent charity
Smell training isn't a cure but can bring improvements for those who have lost their smell through injury and accident.
This innovative training can take many years of practice and patience.
It's an issue those affected are keen to talk about to increase awareness of a condition that can have such a huge impact on everyday life.