I haven't looked into the research on this in a long time but I do recall a study or two showing that certain fragrance oils can have an effect on brain waves. (Either stimulating or relaxing you.) I've never seen anything showing that they have specific effects on skin or reducing nausea. 

I'm not sure if I would consider very scientific everything I read in this article, but Kanebo, a brand owned by the Japanese Kao Corporation, published a really interesting article about that.

We know they have incredible consituents for skin, like phytosterols and polyphenols, along with the fatty acids.  So we know those all do amazing things, and have been studied for it - they repair skin damage, and some have been shown as burn or wound healers, while others interfere with the processes of damage that generally increase with aging.  Something else might be amazing for acne and inflammation, and a lot of phytoestrogens (which leave the body quickly and are great for most people) are easy to find too, along with occasionally high proportions of vitamins like A, C or E.  Some also show dramatic improvements in skin elasticity and wrinkling, and include organic sun protection, while this again is the constituents.   

It seems like the studies (funded I'm guessing, by big cosmetics?) are on those chemical components, so finding more about using the whole oil is another thing.  I haven't looked that hard yet, and have seen eos do amazing things in other contexts, but the studies do seem sparse.  After all, how much makes a difference is obviously key, and I hate seeing that they'd rather just study one chemical - way more expensive, and so much less information.  I'm still very new to cosmetic study though, so maybe it's out there - I did find a link saying that pubmed.gov has a lot on medicinal effects (and haven't looked there yet), and occasionally there's an article that hits on a lot of concrete stuff, it just isn't usually for the whole plant oil.  I have seen one blogger I like calculate how much of something will work ! and share it, so that's impressive.   

Whoa, just found a list of links on relevant science at the same blogger's site - sorry about not knowing how to format that for a new tab.  Of course lavender is the most studied, and I'm unusual in not really liking it, the scent I mean.  Something else on lavender, and something here about research on eos.  I did check Beauty Brains, but there's so much stuff - think it's looking like the question is too big, so here are the links at pubmed - I may get to them eventually!         

I thought the question was about aromatherapy. That's different than applying oils to skin. 

The question is about the "real" effects of essential oils. It could be aromatherapy, skincare etc. Since Right brain did point out that it is known that they have an affect on the brain waves (aromatherapy), I was still wondering about their effects in the skincare or even hair care even. Not just carrot seed oil, but its written that rosemary and peppermint oil have good benefits for hair. I am not sure if this is scientifically proven. 

Rosemary and peppermint oils don't do anything for hair.