Many medications, period and modern can be absorbed through the skin. Persons working in the factory and handling on a daily basis could easily pick up an affinity for the med or develop a high tolerance for it. Most men's meds for prostate or bladder problems come with a very strident warning againt the handling of the pills OR residue by women because it will do nasty things to the reproductive system. In paramedic school we read accounts of workers dealing with nitroglycerin who would rub it in the sweatbands of their hats so as to avoid the headache when they went back to work the next day. About the only thing skin won't absorb readily is water and blood.
your obedient servant,
Surgeon, 2nd Brigade
"not really a surgeon, but I did stay at a Holiday Inn Express"