Liquid oils
Updated
The liquid oil is the part the customer actually feels, and the part with a clock on it.
What the oil is for
It softens the stick so it deposits, carries whatever flavor or active you add, and decides the finish: matt, satin or glossy.
It is usually a quarter to a half of the formula by weight, and it is the ingredient most worth spending money on, because it is what the product feels like.
The stable ones
Jojoba is a liquid wax rather than a true oil, which is why it barely goes rancid. Expensive and worth it in a product this small.
Fractionated coconut is stable, cheap and characterless, which makes it a good diluent and a poor whole answer.
Castor is the gloss ingredient. Thick, sticky, and the reason a tinted balm shines. A little transforms the finish; a lot is tacky.
Mineral oil is stable, cheap and effective, and it is on the monograph list at 50 to 100 percent. It is out of fashion with the customer this category usually sells to, which is a market fact rather than a technical one.
The ones that go off
Sweet almond, avocado, hemp, rosehip, sunflower. All lovely, all unsaturated, all on a clock.
Rancidity in a lip product is not a subtle problem: the customer tastes it. And a tube lives in a pocket at body heat, which is roughly the worst storage condition you could design.
Vitamin E slows oxidation. It does not stop it, and it is not a preservative, an anhydrous balm does not need a preservative because there is no water for anything to grow in.
Reading a shelf life
The finished balm is as short-lived as its shortest-lived oil, and that clock started when the supplier pressed it, not when you opened the bottle.
Buy small, buy often, ask for the pressing date rather than the best-before, and store stock cold and dark. Most rancidity in a finished product was already underway in the drum.