"Getting used to it" is actually due to lesions of the nasal olfactory epithelium tissue and mucosal degeneration and necrosis. Even at low levels.
The vapor liquifies when it contacts the mucous membrane of the mouth and you are actually ingesting monomer....which can also result in adverse central nervous system effects including headache, sleepiness, dizziness, slurred speech and blurred vision. That was my experience after working in an unventilated environment for a year. Not everyone is as sensitive in the short term but I'd take precaution to protect yourself from any sort of neuropathy later in life..... as well as the health of your employees.