The idea that our skin is permeable to smells seems really weird, but there have been a number of documented cases where pets seem to detect similar sicknesses in their owners.
Part of it is I don't think we realize how weird and sensitive smell is even for us. Imagine the world through the nose of a dog or bear.
For Parkinson's the odor comes from chemicals expressed by sebaceous glands.
I didn't know this until reading your comment. It does seem weird that the skin is so permeable, so I looked it up. At least in this case, it doesn't seem to have anything to do with permeable skin.
EDIT: It's mentioned in passing in the linked article: "For one experiment in Manchester, sebum samples were taken from the upper backs of test participants." Other sources are more clear about the relationship to sebaceous glands.
Well pointed, thank you. I did some looking and it seems the 'dog sniffing ovarian cancer through the belly' hasn't been reproduced in any controlled study yet (that i could find). Could just be via breath/skin secretions/etc.
Dogs can smell so tiny concentrations I'd be surprised to find out they could not smell ovarian cancer. Instead, the trick I imagine is to train them to care and alert a handler.
> ... The birds proved to have a remarkable ability to distinguish benign from malignant human breast histopathology after training with differential food reinforcement; even more importantly, the pigeons were able to generalize what they had learned when confronted with novel image sets. ...
> ... However, when given a different (and for humans quite difficult) task—namely, classification of suspicious mammographic densities (masses)—the pigeons proved to be capable only of image memorization and were unable to successfully generalize when shown novel examples. ...
Part of it is I don't think we realize how weird and sensitive smell is even for us. Imagine the world through the nose of a dog or bear.