Sharomix

Overview

Sharomix is a family of broad-spectrum preservative blends sold in many small variants — Sharomix 705, 706, 732, AMP, and so on. The variants differ slightly in the ratio of components, but the most common Sharomix combination on the DIY market — and the one this entry covers — is benzyl alcohol + benzoic acid + sorbic acid.

If that sounds familiar, it should. Sharomix sits in the same chemistry family as Cosgard, Geogard ECT, and Euxyl K 903 — all built around benzyl alcohol as the bacteria-killer paired with one or two organic acids that handle moulds and yeasts. The practical difference between them is mostly which acid does the antifungal work (dehydroacetic for Cosgard, sorbic+salicylic for Geogard ECT, benzoic+dehydroacetic for Euxyl K 903, sorbic+benzoic for Sharomix).

For a hobbyist, Sharomix is mostly a “if your local supplier carries it, it works” option. In the UK and continental Europe it shows up at small natural-cosmetics suppliers; in the US it is less common. It is paraben-free and formaldehyde-free, and the benzoic acid component is on the Ecocert positive list — but the finished blend is not always certified, so check the specific variant if certification matters to you.

What it does in a formula

Primary role: broad-spectrum preservation in low-pH water-based formulas. Benzyl alcohol handles bacteria. Benzoic and sorbic acid together handle yeast and mould.

Worth knowing: both benzoic and sorbic acid are very common natural food preservatives — sorbic acid is what keeps your jam from moulding. Their cosmetic role is identical to their food role, just at much lower percentages.

How to use

Use at 0.8-1.2% of the total formula (the standard range across supplier recommendations).

Add to the cool-down phase, below 40°C. The benzoic and sorbic acids are volatile and degrade with heat, so adding too early kills the antifungal coverage.

Sharomix only works at low pH. The benzoic acid pKa is around 4.2 and the sorbic acid pKa is around 4.8, which means both need to be in their undissociated (uncharged) form to be active — and they only stay that way below about pH 5.5. Above pH 5.5, Sharomix loses most of its antifungal punch. Above pH 6, it stops working entirely.

This is a tighter pH window than Cosgard (which goes up to 6) and much tighter than Optiphen (which goes up to 8). Sharomix demands very acidic formulas.

Like its cousins, Sharomix has limited water solubility because of the benzyl alcohol portion. Best used in emulsions or with a solubiliser in clear watery formulas.

Best for / Worst for

Best for: low-pH facial serums, vitamin C formulations (which sit at pH 3-3.5), exfoliating toners with lactic or glycolic acid, anything where the natural pH is already in the 3.5-5 range.

Worst for: standard skincare emulsions that sit at pH 5-5.5 — too borderline. Hair products that sit above pH 5. Anything above pH 6. Also a poor choice for clear watery toners without a solubiliser.

Common pitfalls

Treating it like Cosgard or Geogard ECT: Sharomix has a narrower pH window than either. If your formula sits between pH 5 and 6, Sharomix is risky. Stick with Geogard ECT or Euxyl K 903 in that range.

Buying the wrong variant: there are at least six Sharomix products in circulation (705, 706, 732, AMP, CV, Plus). They have different INCIs and different pH windows. The variant covered here — benzyl alcohol + benzoic + sorbic — is the most common, but always check the supplier’s spec sheet.

Sorbic acid degradation: sorbic acid is one of the more fragile preservative components and degrades with light, heat, and metals. Store Sharomix in a dark bottle, never above 40°C, and consider adding a chelator (disodium EDTA at 0.1%) in metal-rich formulas.

Sorbic acid yellowing: products preserved with sorbic acid sometimes develop a yellow tint over months. A small amount of tocopherol (0.2%) or sodium metabisulfite slows this.

Substitutes

• Geogard ECT — same family, broader pH range (up to 8), Ecocert-certified, distinctive marzipan scent.
• Cosgard (Geogard 221) — works up to pH 6, less likely to fail in standard skincare emulsions.
• Euxyl K 903 — similar profile, slightly broader pH range, includes a tocopherol antioxidant.
• Optiphen — for formulas above pH 6, where Sharomix will not work.