Grape seeds are advertised as having high levels of a polyphenol called proanthocyanidin, which offers strong anti-oxidant properties. Unfortunately, this is a water soluble polyphenol, which means you don't find a lot - if any - in the oil! It also contains tannins and catechins, both of which can make an oil feel drier than something like sunflower oil (which is also high in linoleic acid).
Resveratrol is a phytoalexin, which is an anti-microbial excreted by plants when under attack. You've probably heard how red wine is supposed to be good for us because it contains this polyphenolic compound, and there is the possibility that it makes it into grape seed oil if it is pressed from a pomace, but again, not a lot of it makes it into the actual oil we use.
And we do find some nice phytosterols in this oil in the 0.8% to 1.5% unsaponifiables. It contains campesterol, B-sitosterol, and stigmasterol, all of which help with barrier repair, reduction of inflammation, and reduction of itching.
Although grapeseed oil offers some great qualities to a bath and body product, it can go rancid very quickly. Adding 1% Vitamin E might retard the rancidity a while, but it really is an oil that can be too unstable to use in products that you might give or sell to someone else. For yourself it's fine - you can put a best before date on it and make sure you'll use it up - but when it gets into someone else's hands, you have no idea how long they'll store it before using it. (I found this out the hard way - I used it in bath bombs and I could smell a really rancid smell in a few weeks. I have no idea how long the oil has been on the suppliers' shelves and then it might take me a while to get around to using it, so I haven't used it much, except for cooking.)
That's not to say you shouldn't try using it - with all that great linoleic acid you'll get some barrier repair, moisturizing, and reduction in transepidermal water loss. The phytosterols can help with reduction of inflammation and itchiness. And the catechins might be anti-microbial.
It makes a good massage oil because it is light and dry, and you can use it wherever you might use a high linoleic oil like sunflower oil or soy bean oil.
Join me tomorrow for fun with hemp seed oil!