Preserving water-based batches safely
Why every leave-on, water-based lotion or cream must be preserved, how Hi Ellie computes the minimum dose from your own pantry preservative, and the pH range to confirm before you bottle.
Lotions, creams, and body butters with a water phase are a Bath & Body recipe with no lye involved — but anything containing water carries its own risk: it's a place for microbes to grow.
Why water-based products must be preserved
Mold, bacteria, and yeast grow readily in water. An unpreserved or under-dosed leave-on lotion is a real microbial-contamination and product-safety risk, not a cosmetic nice-to-have.
Anhydrous, all-oil products (like a solid body butter with no water phase) don't need a preservative. But a preservative is not the same thing as an antioxidant — an antioxidant slows oil going rancid, a preservative stops microbial growth. Know which one your batch actually needs.
The cool-down phase
A lotion's water phase and oil phase are emulsified together while hot, then the batch is cooled. The preservative goes in during this cool-down phase, below its own heat-sensitive threshold. Heat destroys many preservatives, so adding it too early — while the batch is still hot — quietly ruins the protection without any visible sign that anything went wrong.
How Hi Ellie doses it
The wizard computes the minimum required preservative weight from your own stocked pantry preservative and its on-file effective rate — never a number from the general catalog, and never an invented figure. That computed amount is a floor: never go below it.
Heads up: if you swap which preservative you're using, the minimum dose and the working pH range both change with it — they're specific to the preservative you actually stocked, not a generic rule of thumb.
Confirm your pH before bottling
A preservative only works inside its own stated pH range, so before bottling, check your batch with a pH strip or meter rather than assuming.
But that working range is not a target you can sit anywhere inside. Several common preservatives stay effective well down into the acidic range — Liquid Germall Plus, Geogard ECT and Phenonip are all documented from about pH 3 — and a leave-on lotion sitting near the bottom of a range like that is properly preserved and acidic enough to sting or leave skin irritated after a full day's wear. It's a matter of degree, not a line: pH 4.3 is unremarkable, pH 3 is not. A rinse-off product is a different story again; a bar of soap is routinely pH 9–10 and washes straight off.
So for a leave-on lotion, Hi Ellie shows you the overlap of two things: the range your preservative needs, and roughly pH 4.5–6.0 — a band whose floor is about where skin itself sits and whose ceiling keeps the batch on the acidic side of neutral. That's your target. Where a preservative only works outside that band entirely, Hi Ellie says so on the recipe instead of splitting the difference — the fix is a different preservative, not a compromise pH.
Which direction you miss the target in matters, and the step tells you which is which for the preservative you actually stocked. When the bound you cross is the band's rather than your preservative's, it's a comfort problem first — going low means the batch is drifting acidic, and the further down it goes the more likely it is to sting or leave skin irritated; going high just means it's drifting alkaline, which isn't where something worn all day should sit. When the bound you cross is your preservative's own — for a preservative like Optiphen Plus, documented pH 4.0–6.0, that 6.0 is the edge of its documented range — you're outside what the manufacturer's data covers, and the batch can no longer be counted on to stay preserved.
Neither direction comes with a promise that the batch is still protected out there. A range saved as 4.0–6.0 is the range the manufacturer documented, not a proof of what happens either side of it, and a preservative can have no lower bound on file at all (Leucidal Liquid SF is one) — no stated floor is not evidence that it works down there. If a reading lands outside the target, bring it back before you bottle rather than reasoning about how far out is still fine.
On that 4.5–6.0: it's a widely-used formulation convention for leave-on skincare, not a figure transcribed from a standards body — unlike the dose rates and pH windows on your preservative entries, which come from manufacturer data sheets. Your preservative's range is the hard constraint; treat this as the sensible place to aim inside it.
Broad-spectrum and shelf life
Choose a broad-spectrum preservative so you're covered against bacteria, mold, and yeast together, follow its on-file usage rate, and don't stretch a batch past its intended shelf life just because it still looks and smells fine.