The hazardous material data sheet for acetaldehyde drives home just how dangerous this stuff is. It is highly flammable, reactive, and poses a health hazard in the industrial workplace unless utmost precautions are exercised in its handling.
Although acetaldehyde appears as a transient structure in the biochemistry of the body, it is safely secured within enzymes when it is being used in this manner in a reaction. It is not allowed to come into random contact with other body structures by drifting freely in the cellular milieu or bloodstream...unless of course, it has arrived there through the unexpected route of budding yeast (Candida Albicans) metabolism. If you are not aware of this potential threat or are doing nothing about it even if you are, then you are at risk for downstream symptoms.
It is intriguing to note that under certain conditions acetaldehyde can spontaneously ignite at room temperature and burn with a blue flame.