Optiphen™ Plus

What is it? Optiphen™ Plus is a broad spectrum preservative that works well to preserve products like lotions, creams, cleansers, and shampoo bars. Due to its phenoxyethanol content it is not natural, but is often considered ‘more’ natural than Liquid Germall™ Plus.

Optiphen™ Plus is approximately 52% phenoxyethanol, 42% caprylyl glycol, and 6% sorbic acid (source).

INCI Phenoxyethanol (and) Caprylyl Glycol (and) Sorbic Acid
Appearance Clear semi-viscous fluid
Usage rate 0.75%–1.5% (I usually use it at 1.5%)
Scent Nothing really noticeable, especially in a finished formulation.
Approximate Melting Point Liquid at room temperature.
Effective pH range Works best at a pH below 6
Solubility Due to its phenoxyethanol content Optiphen™ Plus has limited solubility in water, but good solubility in ethanol, isopropanol, ethylene glycol, propylene glycol, butylene glycol, and glycerin.

Because of its limited water solubility Optiphen™ Plus isn’t a great choice for preserving really watery formulations like hydrous serums.

Why do we use it in formulations? Optiphen™ Plus preserves our formulations so they don’t grow mould and get all gross and icky.
Do you need it? No, but it is a good preservative choice and I like having it on hand.
Refined or unrefined? Optiphen™ Plus only exists as a refined product.
Strengths Effective and versatile preservative with relatively high heat tolerance (up to 80°C [176°F]), making it a good choice for using in products that need a preservative but will be too solid to add one at typical cool down phase temperatures (~40°C and cooler).
Weaknesses Optiphen™ Plus is not very water soluble and as such doesn’t work very well in watery products like hydrous serums unless the formulation includes a compatible solvent.
Alternatives & Substitutions You’ll need another broad spectrum preservative.

I use Liquid Germall™ Plus a lot; it is more water soluble than Optiphen™ Plus but has a lower heat tolerance.

Optiphen™ (INCI: Phenoxyethanol [and] Caprylyl Glycol) is a good option. Plain phenoxyethanol can also work, depending on the formulation.

How to Work with It Optiphen™ Plus can be hot or cold processed as long as your heated phase doesn’t exceed 80°C (176°F). I usually include it in the cool down phase of emulsions.

For the best performance, ensure formulations preserved with Optiphen™ Plus have a pH below 6.

I’ve had great experience using it in emulsions and low-water content formulations like shampoo bars and conditioner bars.

If you want to use Optiphen™ Plus in a watery formulation like a hyaluronic acid serum, pre-distribute it in a suitable solvent (glycerin, propylene glycol, and propanediol 1,3 are probably the easiest options) before adding the water. I’d try using 3–5x the amount (eg. 1.5% Optiphen™ Plus, 4.5–7.5% solvent) and see how that works. (This strategy was suggested to me by cosmetic chemist Valerie George from Simply Ingredients.)

Storage & Shelf Life Stored somewhere cool, dark, and dry, Optiphen™ Plus should last two years.
Tips, Tricks, and Quirks I find Optiphen™ Plus tends to lower the pH of formulations a little bit, and that can be really useful.
Recommended starter amount 30g (1.06oz)
Where to Buy it  Buy it from an online DIY ingredient supplier.

Some Formulations that Use Optiphen™ Plus

Geogard® ECT

What is it? Geogard® ECT is a liquid natural broad-spectrum preservative from Arxada.

It is comprised of (source: Arxada):

  • Benzy alcohol: 77–86%
  • Salicylic acid: 8–15%
  • Glycerin: 3–6%
  • Sorbic acid: 1–4%

It is also sold under many other names like Preservative Eco, Mikrokill ECT, and Plantaserv M, so be sure to check the INCI on what you’re purchasing.

Geogard® ECT is part of the Geogard® line; the “ECT” is important as the different products within the line all have different INCIs. Other Geogard® products include Geogard Ultra®, Geogard® 221, Geogard® 111S, Geogard® 111A, and Geogard® Boost PHC.

INCI Benzyl Alcohol (and) Salicylic Acid (and) Glycerin (and) Sorbic Acid
Appearance Pale yellow liquid
Usage rate 0.6–1%
Scent Almondy/marzipan-y
pH Effective from 3–8.

Geogard® ECT will cause the pH of your formulations to drop.

Solubility While the product description on UL Prospector says Geogard® ECT is water soluble (as of May 2024), the data sheet states that it works best in emulsified systems.

In my experience, Geogard® ECT does not mix well into totally hydrous formulations like watery serums and room sprays.

Why do we use it in formulations? Geogard® ECT protects our formulations from microbial spoilage (bacteria, yeast, fungus); I’ve found it to be an effective and easy-to-use natural preservative option.
Do you need it? You should have at least one broad-spectrum preservative; Geogard® ECT is a decent choice if you prefer natural preservatives and don’t mind the almondy scent.
Refined or unrefined? Geogard® ECT only exists as a refined product.
Strengths Unlike many natural preservatives, Geogard® ECT has a maximum functional pH range of 8 (most natural preservatives require an acidic pH to function well).

The manufacturer lists lip products as a possible application.

Weaknesses Noticeable almondy scent that can get stronger as the formulation ages.

Can cause the pH of a formulation to drop so much that it needs to be raised (dropping to below 4 is not uncommon). This can also be problematic if your emulsifier doesn’t work at lower pHs as your emulsion could break when the preservative is added, so you’d need to include a base in the formulation to prevent that large pH drop before you added the preservative.

Due to the salicylic acid content, Geogard® ECT cannot be used in products for children under 3 except for shampoo.

If you are using Geogard® ECT to preserve a formulation that contains salicylic acid as a skincare active, the salicylic acid content in the preservative will count towards the maximum allowable concentration of 2%. If we assume Geogard® ECT contains 15% salicylic acid, when used at 1%, the overall formulation will contain 0.15% salicylic acid. This leaves room for 1.85% additional salicylic acid.

Alternatives & Substitutions You’ll need another broad-spectrum preservative. Liquid Germall™ Plus is an effective, versatile choice, but it isn’t natural. Natural alternatives include Geogard Ultra™; and Euxyl k 903, though both have a lower effective pH range, and Geogard Ultra™ requires a buffer system to prevent downwards pH drift over time.
How to Work with It Include Geogard® ECT in the cool down phase of your formulations, and ensure the final pH of the formulation is the in 3–8 range.
Storage & Shelf Life Stored somewhere cool, dark, and dry, Geogard® ECT should last at least a year.
Tips, Tricks, and Quirks Looking for a natural way to add an almondy scent to your formulation? Preserve it with Geogard® ECT!
Recommended starter amount 30mL (1fl oz)
Where to Buy it Purchase Geogard® ECT from an online DIY ingredient supplier. It can be helpful to do a Google search for the INCI as this product is sold under a variety of names.

Some Formulations that Use Geogard® ECT

Euxyl™ k 903

What is it? Euxyl™ k 903 is a liquid natural broad spectrum preservative manufactured by Ashland. It is compatible with non-ionic, anionic, and cationic formulations.

Euxyl™ k 903 is comprised of (source: Formulator Sample Shop):

  • Benzyl alcohol: 78–84%
  • Benzoic acid: 11–13%
  • Dehydroacetic acid: 6.5–7.5%
INCI Benzyl Alcohol (and) Benzoic Acid (and) Dehydroacetic Acid (and) Tocopherol
Appearance Clear yellow liquid
Usage rate 0.4–1.2%; tests from Ashland show it is effective at 0.8–1%
Scent Slight chemically scent with a vague almondy whiff. This scent is soft but noticeable in products that are otherwise unscented.
pH 3.0–4.0
Solubility Euxyl™ k 903 is approximately 1.2% soluble in water and readily soluble in polar solvents.

From Ashland: “Euxyl™ k 903 preservative is only limitedly soluble in water. 100g of water at 20°C dissolve 1.2g of Euxyl™ k 903 preservative. In polar solvents such as 1,2-propylene glycol, propanol or acetone, Euxyl™ k 903 preservative is readily soluble. In polyalcohols such as glycerol and sorbitol Euxyl™ k 903 preservative is moderately soluble. In aliphates with hydrophilic groups such as 2-octyldecanol and isopropyl myristate, Euxyl™ k 903 preservative is limitedly soluble. In pure aliphatic solvents it is slightly soluble.”

Why do we use it in formulations? Euxyl™ k 903 is a preservative; we include it in our formulations to ensure they don’t grow gross things like mould and fungus.
Do you need it? You should have at least one broad-spectrum preservative; Euxyl™ k 903 is a good choice if you prefer natural preservatives.
Refined or unrefined? Euxyl™ k 903 only exists as a refined product.
Strengths Easy to use broad-spectrum preservative. I find Euxyl™ k 903 doesn’t lower the pH of formulations as much as Geogard® ECT and Geogard Ultra™ do.
Weaknesses It does add a bit of a chemically smell to unscented formulations, and I find it thins emulsions a bit.
Alternatives & Substitutions You’ll need another broad-spectrum preservative. Liquid Germall™ Plus is an effective, versatile choice, but it isn’t natural. Natural alternatives include Geogard Ultra™; and Geogard® ECT.
How to Work with It Include Euxyl™ k 903 in the cool down phase of your formulations. It is somewhat heat stable (Ashland states a maximum temperature of 80°C for no more than 4 hours), but the manufacturer still recommends including it in the cool down phase.

Euxyl™ k 903 works best in a pH range of 3–6, with 5–5.5 being recommended. This preservative is more effective at lower pH ranges. I find it lowers the pH of formulations ~0.75–1.5 pH points, depending on the formulation. This drop can often be enough to take the product into the effective range for the preservative.

Storage & Shelf Life Stored somewhere cool, dark, and dry, Euxyl™ k 903 should last a year.
Tips, Tricks, and Quirks “In formulations as a result of the presence of iron ions, e.g. from mineral thickeners, yellow discolorations were observed.” –Ashland
Recommended starter amount 30mL (1fl oz)
Where to Buy it  Buy it from an online DIY ingredient supplier. Mine was a gift from Formulator Sample Shop.

Some Formulations that Use Euxyl™ k 903

Geogard Ultra™

What is it? Geogard Ultra™ is a natural broad-spectrum preservative manufactured and patented by Arxada (formerly Lonza). The INCI is often stated as just Gluconolactone (and) Sodium Benzoate, but if you review the data from Lonza, Calcium Gluconate is included at 1%.

From Lonza: “Geogard Ultra™ is a synergistic and patented blend comprised of gluconolactone and sodium benzoate. Aside from its proven broad spectrum activity, wide range of global regulatory approvals and broad formulation compatibility, it also contributes an added skin moisturisation benefit and has conformance with ECOCERT/COSMOS, NATRUE and the Soil Association. What makes this preservative unique is the synergy between the two ingredients which allows for its broad spectrum efficacy. Typically, organic acids on their own are too weak and often require a co-preservative or booster in order to perform optimally. The gluconolactone in this blend works in conjunction with the sodium benzoate to act as an efficient preservative booster, slowly releasing gluconic acid over time thereby contributing to the broader preservation effect.”

Read this document to learn more. It’s not the most recent version, but it’s the newest version I’ve found that’s not behind a login wall.

Geogard Ultra® is part of the Geogard® line; the “Ultra” is important as the different products within the line all have different INCIs. Other Geogard® products include Geogard® ECT, Geogard® 221, Geogard® 111S, Geogard® 111A, and Geogard® Boost PHC.

INCI Gluconolactone (and) Sodium Benzoate (and) Calcium Gluconate
Appearance Coarse white powder
Usage rate 0.75–2%
Scent Nothing noticeable in end products
Approximate Melting Point Solid at room temperature
pH range 3–6
Charge compatibility Cationic, anionic, and non-ionic compatible.
Solubility Geogard Ultra™ is soluble up to 4% in water, dispersible in glycols and alkyl sulphates.
Why do we use it in formulations? Geogard Ultra™ protects our products from microbial spoilage (bacteria, yeast, fungus). I’ve found it to be a good natural preservative option.
Do you need it? If you’ve already got Liquid Germall™ Plus you don’t need this preservative. However, if you’re looking to start working with more natural preservatives, Geogard Ultra™ is a fairly good option, though I would not call it beginner friendly due to its tendency to pH drift.
Refined or unrefined? Geogard Ultra™ only exists as a refined product.
Strengths Readily available water-soluble natural preservative with broad applications.
Weaknesses Geogard Ultra™ can cause the pH of formulations to drift downwards, so make sure you’re testing its performance and consider including a buffer in your formulation.

This is what the manufacturer recommends (copied from this source):

“To maximise the pH stability of the final formulation, it may be necessary to employ use of a sodium citrate buffer and pH adjustment as described below…

    1. Dose the final product with the required level of Geogard Ultra™ along with a 1.5x amount of sodium citrate. So, a 2% dose of Geogard Ultra™ should be accompanied by 3% sodium citrate.
    2. Mix thoroughly to ensure all solids have dissolved and adjust the pH of the formulation to 7.00–7.25 with a 30% sodium hydroxide (NaOH) solution.
    3. Finally, adjust the pH to desired final product pH (pH 5.4–5.5 is ideal) with dilute sodium hydroxide or citric acid solution.”

Due to the possibility of Sodium Benzoate and ascorbic acid (vitamin C) combining to create benzene, it is not recommended to use Geogard Ultra™ in formulations containing ascorbic acid. I have read that it should also be avoided in formulations containing citric acid, but as you can see above, the manufacturer recommends citric acid to adjust formulations made with Geogard Ultra™, so Geogard Ultra™ and citric acid are likely an ok combination.

Alternatives & Substitutions Please read this FAQ.
How to Work with It Geogard Ultra™ is not heat sensitive, so you can include it in the heated water phase of your products if desired. If cold processed it will take a while to dissolve; I will often cover my beaker with clingfilm and leave it to dissolve overnight.
Storage & Shelf Life Stored somewhere cool, dark, and dry, Geogard Ultra™ should last at least two years.
Tips, Tricks, and Quirks I find Geogard Ultra™ noticeably lowers the pH of products; I’ve created several formulations with it that I thought would need to have acid added to them but ended up needing the pH raised instead.
Recommended starter amount 30g (1.06oz)
Where to Buy it  Buy it from an online DIY ingredient supplier.

Want to learn more about preservatives and compare them? Check out this chart!

Some Formulations that Use Geogard Ultra™

Liquid Germall™ Plus

What is it? Liquid Germall™ Plus is a broad-spectrum preservative that is effective in a wide variety of formulations and pH environments.

The limiting ingredient in Liquid Germall™ Plus for regulatory purposes is the Iodopropynyl Butylcarbamate. The maximum usage rate of 0.5% Liquid Germall™ Plus results in 0.002% Iodopropynyl Butylcarbamate in finished formulations, which is below the maximum usage rate for leave-on and rinse off purposes in the USA, EU, and Japan. In the EU, Iodopropynyl Butylcarbamate is not to be used on children under 3 years of age unless in rinse-off products. No such restriction exists in the USA or Japan, so I’d say it’s up to you if you wish to use this preservative in leave-on products for people under 3 years.

Liquid Germall™ Plus is a patented product made by Ashland.

INCI Propylene Glycol, Diazolidinyl Urea, Iodopropynyl Butylcarbamate
Appearance Viscous clear liquid
Usage rate 0.1–0.5%, though Ashland reports efficacy as low as 0.06% and recommends higher concentrations for more complex formulations. I’ve never encountered spoilage at 0.5%, even in very challenging formulations.
Scent Nothing noticeable in end products
Approximate Melting Point Liquid at room temperature
pH range 3–8
Charge compatability Cationic, anionic, and non-ionic compatible.
Solubility Liquid Germall™ Plus is water-soluble.
Why do we use it in formulations? Liquid Germall™ Plus protects our products from microbial spoilage (bacteria, yeast, fungus). I’ve used it for years in all kinds of formulations and have found it to be an incredibly reliable, effective preservative.

In addition to its versatility in terms of efficacy, it also works over a broad pH range, generally negating the need to test the pH of your end product unless you know it contains high concentrations of extremely acidic or basic ingredients. If you don’t want to invest in pH testing equipment, this is a great added bonus!

Do you need it? highly recommend it. Even if you don’t want to use it forever, it’s a great starter preservative, allowing you to familiarize yourself with other aspects of making and formulating without worrying about preservation.
Refined or unrefined? Liquid Germall™ Plus only exists as a refined product.
Strengths It is very effective at low concentrations, and functions in a wide variety of formulations. According to Ashland, Liquid Germall™ Plus “is compatible with virtually all cosmetic ingredients including complex ingredients such as proteins and surfactants.”
Weaknesses Liquid Germall™ Plus can be very hard to find outside of North America.
Alternatives & Substitutions Please read this FAQ.
How to Work with It Add Liquid Germall™ Plus to the cool-down phase of your formulations; do not heat above 50°C (122°F).

Liquid Germall™ Plus is not approved for use in aerosols, but it is ok for use in products packaged in mister/spray bottles. This is because the mists made by mister bottles are nowhere near as fine as an aerosol mist is. Ashland, the manufacturer of Liquid Germall™ Plus, has shared several sample “spray” formulations preserved with Liquid Germall™ Plus.

Storage & Shelf Life Stored somewhere cool, dark, and dry, Liquid Germall™ Plus should last at least two years.
Tips, Tricks, and Quirks Diazolidinyl Urea is considered safe up to 0.5%; given it is just a component of the overall product with a maximum usage rate of 0.5%, we’re well below that.

Iodopropynyl Butylcarbamate is present at 0.004% in Liquid Germall™ Plus; 0.5% usage means a finished formulation will contain 0.002% Iodopropynyl Butylcarbamate. This is well below the CIR limit of 0.1%.

Recommended starter amount 30g (1.06oz)
Where to Buy it  Buy it from an online DIY ingredient supplier.

Want to learn more about preservatives and compare them? Check out this chart!

Some Formulations that Use Liquid Germall™ Plus