I asked this question a while back and never really got a scientific answer, and I’m still curious.
Why is it that inhaling eucalyptus or other menthol vapours clears your nasal passages? Is it related to that cooling sensation that menthol produces on the skin? And come to that, why exactly does menthol feel “cold” anyway?
Not sure about why it clears your nasal passages but on the subject of making your skin feel cold I believe it is common to all alcohols (such as the swab on your arm before an injection). I believe it is simply down to the alcohol evaporating and taking with it some of the heat in your skin, much the same as sweat works by absorbing heat and evaporating thus taking heat away from the skin.
I’m sure someone will correct me if what I posted was wrong 
I wish this site had an edit button, here is a small snippet of info for you from www.fgb.com.au on the subject of eucalyptus oil.
But menthol, even at small concentrations in, say, chewing gum, makes your mouth feel cold, while ethanol at 40% in vodka doesn’t. Surely there’s something else at work other than simple evaporation?
I don’t know the exact details of it, but menthol does actually stimulate the same nerves that sense cold - it’s not just an evaporation thing.
I got nuthin’ on the eucalyptus, though.
From this site Western Oil Mallee Project
The rest of the article is actually based on using eucalyptus oil in place of non-environmentally friendly industrial solvents. Eucalyptus oil is extremely versatile.
Hope this has been of some use.
I got nuthin’ on the menthol, though.
I should have added that Allan Barton is Associate Professor in Chemistry at Murdoch University in Western Australia.
Cheers!