What it is
Grapeseed oil is solvent-extracted from the seeds left over from wine production. At roughly 70% linoleic acid it's one of the most polyunsaturated oils available. It became a product because the seeds were a free leftover, not because anyone needed the oil.
Why it's in your food
It's sold as a light, clean, high-smoke-point oil for sautéing and dressings, and appears in “gourmet” and “better-for-you” product lines. The smoke-point marketing is both the selling point and the catch.
Why your biology objects
~70% linoleic acid, nearly as polyunsaturated as safflower, with the same peroxidation path to OXLAMs. The high smoke point is the catch: the heat it's sold for is exactly what oxidizes it fastest.
The ancestral lens
There was no grapeseed oil before industrial solvent extraction. Pressing a usable oil from grape seeds takes hexane and refining, so it's a modern product delivering a modern dose of linoleic acid, a fat your biology met at a small fraction of today's levels.
Dose & context
Smoke point measures when an oil visibly burns, not when it oxidizes. Polyunsaturated fats like this one start forming oxidation products well below their smoke point, so the high-heat cooking it's marketed for is close to a worst case.
Label tricks
“High smoke point” is sold as a safety feature, but for a polyunsaturated oil it mostly means you'll cook it hot enough to oxidize it. “Light” refers to flavor, not calories or healthfulness.
What to reach for instead
For high heat, monounsaturated and saturated fats (avocado oil, olive oil, ghee, tallow) are far more stable and tolerate the temperatures grapeseed is marketed for without the same oxidation.
Straight answers
Is grapeseed oil healthy?
Its linoleic acid content (~70%) is near the top of all oils, and that fat oxidizes readily under heat. The “light, high-smoke-point” marketing doesn't change the underlying fragility.
Is grapeseed oil good for high-heat cooking?
It's sold that way, but smoke point isn't the same as oxidative stability. Polyunsaturated oils oxidize before they smoke, so a stable monounsaturated or saturated fat is the better high-heat choice.
Is grapeseed oil a seed oil?
Yes, and one of the most polyunsaturated, alongside safflower and sunflower.