Is there a relationship between changing body odour and Alzheimer's disease?

Reduced sense of smell is one of the earliest features of Alzheimer's disease. Patients not only smell less acutely, they also recognise and remember odours less well. This is well documented and has been found consistently across multiple studies. Smell tests are therefore being investigated as a screening tool, in which a person is asked to identify or remember a series of familiar odours.

The question many people are asking is a different one: does the body odour of someone with Alzheimer's change in a way that the people around them can detect? That is not what the available studies examine. The evidence relates exclusively to how the patient's own sense of smell deteriorates, not to a changed odour that the person emits.

Why does this sense of smell deteriorate? The loss of specific nerve connections in the limbic system is thought to play a role. That part of the brain is involved in both smell and memory, and is affected early in Alzheimer's disease. Animal research also points to a possible role for hormonal changes in this process, but those findings currently apply only to mouse models.

There is limited evidence that memories triggered by odours are more vivid and more specific in Alzheimer's patients than memories recalled without an olfactory stimulus. A small study also found that odour-triggered memories came back more quickly. This opens a possible avenue for scent-guided therapy in dementia care, but the study included only a handful of participants, so firm conclusions cannot yet be drawn.

Finally, a reduced sense of smell in older age is also associated with a higher risk of depressive symptoms, and cognitive decline appears to play a mediating role. This makes smell as a signal potentially useful in a broader sense, but also less specific to Alzheimer's disease alone.