First off, there are two types of spoiling we’re worried about: rancidity and microbial (mould/fungus/yeast—living stuff).
Rancidity is a problem with oils, but it takes a very long time to set in. Oils, when kept somewhere cool and dark, will generally last years (though some are more shelf stable than others). You’ll know an oil has gone rancid when it starts to smell off, sort of like very old lipstick or a bag of 10 year old trail mix you found at the back of your pantry.
So, for things that are just made from different oils (body butters, lip balms, massage oils, etc.), rancidity is what you’re worried about, and you’ll generally have a few years before that sets in. You can delay it by adding an antioxidant like rosemary seed extract, grapefruit seed extract, or vitamin E oil. I store yet-to-be-started lip balms and body butters in my fridge.
Mould and other bacterial spoilage becomes a problem when water is involved. That includes emulsions (like lotions), mists and sprays, and things that can be contaminated with water (like a scrub that lives in the shower). Ingredients like witch hazel, rose water, floral hydrosols, aloe vera juice, and milk still count as water when we are considering shelf life—in fact, they count as water plus additional bacterial temptation, and concoctions made with lots of these ingredients are harder (or in the case of milk, impossible) to preserve. The shelf life of something with water will depend greatly on how the concoction was prepared, how clean everything was, and how it is used and stored, so it is impossible for me to give you any kind of a shelf life estimate. Generally speaking, though, things that contain water are probably only good for a day or two without a broad spectrum preservative.
You MUST add a broad-spectrum preservative to recipes that include water. Broad spectrum preservatives are not infallible, though—you can’t just add them to anything and expect it to last forever. Concoctions with lots of delicious bacteria food (herbal infusions, plant extracts, etc.) will eventually spoil regardless of added preservatives, especially because our kitchens are far from sterile. I make things in small batches, avoid as many temptations as possible, add a preservative, and watch for signs of spoilage, as I do with food in my fridge. If you notice changes in colour, scent, or texture, or you see mould or separation, it’s time to chuck it out.
Antioxidants like rosemary seed extract, grapefruit seed extract, and vitamin E oil are not preservatives and will do nothing to extend the shelf life of something that contains water and requires a broad spectrum preservative.
Trying to figure out how much preservative to add to your final product? I made a handy-dandy preservative calculator that you can use here.
Posted in: Preservatives