Short answers:
- Does it contain water, OR will it come into contact with water, and do you intend to keep it longer than a day or two? Yes, you need a preservative.
- If it contains no water, and will not come into contact with water, or if you’ll be using it immediately: No, you don’t need a preservative.
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 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 oil, grapefruit seed extract, or Vitamin E.
Mould and other bacterial spoilage become a problem when water (and time) 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 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.) may 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 are not preservatives and will do nothing to extend the shelf life of something that contains water and requires a broad spectrum preservative.
When it comes to selecting a preservative, make sure you read up on it to ensure it’s compatible with your product. We have listed all this information on our website. Points to consider include:
- Effective pH range: many more natural preservatives have a narrower effective pH range, so if you want to use them you will need to make sure you can accurately test and adjust the pH of everything you make to ensure your preservative is compatible.
- Ingredient compatibility: some preservatives are inactivated by ingredients like PEGs or even vitamin C, so make sure you check and see what’s what/
- Solubility: water-soluble is said to be best as anything that goes wrong in your product will go wrong in the water phase—that said, we have read a lot of debate on both sides of this. Whatever you do, make sure your preservative is soluble in your product (don’t put a water-soluble preservative in a 100% anhydrous product with no emulsifier)
- Maximum temperature: don’t cook your preservative and ruin it. Preservatives typically go into the cool-down phase (below 40°C/104°F), but some products (like solid shampoo bars) are really dang solid at 40°C, so you’ll want to choose a preservative with higher heat tolerance (We like Optiphen Plus for this).
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.
