What it is
E306 is a tocopherol-rich extract — natural vitamin E. Modern commercial production is from soya, sunflower, palm, or wheat-germ oil distillates. Animal-derived tocopherols are theoretically possible but vanishingly rare in modern production.
Why it matters
Antioxidant in fats, oils, infant formula, baked goods, breakfast cereals. Sometimes paired with E300 vitamin C as a "natural" antioxidant pair.
What to do
Default assumption is vegan (plant-sourced). The synthetic alphas — E307 (alpha-tocopherol), E308 (gamma-tocopherol), E309 (delta-tocopherol) — are unambiguously vegan.