Vegetable oils contain high amounts of PUFA (polyunsaturated fatty acids, good fats)which are susceptible to degradation when exposed to heat (even cooking), light, and oxygen. These types of oils can go rancid quickly if improperly stored.
Vegetable oils are often stored in plastic bottles, which further increases light exposure. Plastic bottles contain bisphenol-A (BPA) and similar compounds. These compounds are endocrine disruptors and can cause damage to the reproductive and metabolic health of exposed individuals. BPA is fat-soluble and could easily leech into oils bottled in plastic.