People who struggle to distinguish between the smell of bubblegum and petrol could be at risk of developing dementia, a new study suggests.

Scientists believe that changes in smell could be one of the first signs that a person is suffering from the early stages of Alzheimer’s disease.

It is thought that the first damage to the brain from dementia occurs up to twenty years before any symptoms appear, but currently there is no way to tell if is happening.

But scientists at McGill University, Canada, believe that one of the first changes may be damage to the olfactory neurons, which distinguish between different aromas.

They tested their theory on 300 people who were at high risk of developing Alzheimer’s disease because they had a parent who suffered from the condition. They were asked to take multiple choice scratch-and-sniff tests to identify strong scents, such as bubblegum, petrol and lemon.