The big sniff: why changing the smell of the room you’re in could boost your mood

Introducing a pleasant ambient fragrance is one of the most effective ways to enhance wellbeing

Every home has its own BO, or building odour. But we all become so used to it, we don't realise it is there, except perhaps, fleetingly, when opening the front door on returning from a long trip away.

Sometimes the smells we don't notice - the ones present at such low concentrations that we are not even aware of them, such as a faraway rubbish bin - turn out to exert the biggest impact on our mood and wellbeing. For some, the olfactory ambience of their home can lead to what is known as sick home" syndrome. Thought to be caused by poor ventilation, mould and the accumulation of bad smells, the symptoms include headaches; eye, nose or throat irritation; dry or itchy skin; or mental fatigue. It is a topic of debate whether this is due to physical or psychological responses, but according to researchers, such as professor Joseph Allen at Harvard, it may be because our brains tag unpleasant smells as dangerous and thus keep us on high alert to monitor their source.