Of the 13 vitamins, vitamin E is known to be the best for hair health. It’s one of the four fat soluble vitamins, so you tend to find it in fats. Most raw, unrefined oils are pretty high in this stuff, and since beard oils almost always use such oils, they’re high in vitamin E. You won’t find many beard oils that don’t contain unrefined oils, but look out for any that contain coconut or babasu oil, as these are very often refined and that means less vitamins. Jojoba, almond, and argan oils are great; castor, olive, and grapeseed are decent.
Vitamin E is known to stimulate the growth of capillaries, which provide blood (and thus nutrients) to the follicles. This means stronger, healthier hair growth. This benefit can be imparted either when the vitamin is ingested or when it is applied topically (as with beard oils, or the vitamin E oil you can purchase at the pharmacy).
In this way, beard oils can actually provide some scientific aid in helping your beard hair to grow. And if not simply to grow, then to grow better, stronger, and fuller than otherwise. It’s the same way that eating a diet high in vitamins, protein, and healthy fats will make your body in general healthier; when your beard gets fed vitamin E, it’s just healthier in general.
But it’s important to remember that beard oil is not a magic hair-growth tonic that you apply in the evening to wake up with a full beard the next morning.