Gums, Gels and Thickeners - Choosing the Right Structure for Your Formula

17 minutes ago

5 min read

Can I substitute the one I already have?

You find a formula you’d like to make. You have the oils, the humectants and the preservative. Then you reach the thickener, and it’s one you don’t have.

There’s another gum on your shelf. Can you use that instead?

This is a useful question to explore alongside November’s videos. We’ll be comparing several thickeners at the bench, but having a few choices can also leave us wondering which ones we can exchange in a formula.

Sometimes a substitution is possible. The part that needs more thought is whether we’re trying to reproduce the original product or make a different product with ingredients we already have.

How close do you need the result to be

Suppose you’re making a lotion for yourself. You’re comfortable with a slightly different texture, and you don’t need it to look exactly like the original. That gives you some room to consider alternatives.

Now suppose you’re trying to reproduce a clear gel with a particular feel. You’d be disappointed if it came out cloudy or noticeably stringy. The choice is narrower because more of the original product’s characteristics need to be preserved.

Before changing anything, decide which differences you’re willing to accept. “Can I make something useful with this ingredient?” and “Will this reproduce the original formula?” are separate questions.

Neither question can be answered just by finding another ingredient sold as a thickener.

Find out why it was included

Start with the formula’s notes. Do they explain what the thickener contributes? Is it there for texture, to help keep particles distributed, or to support the emulsion?

If the formulator explains the choice, use that information. If the formula only gives an ingredient name and percentage, there may be more to find out before making a substitution.

A lotion might look just as thick after a change and still develop an oil-rich layer during storage. A thickener can help limit the movement of oil droplets, while the emulsifier helps keep them from joining together. Published work on one polymer system examines those separate jobs. (see sources & references below)

That’s the sort of uncertainty to resolve before making the batch. Look for technical information that supports the proposed ingredient in the same kind of product, and check the complete formula against its limits.

If you can’t establish why the original material was chosen, keeping it is the more cautious choice when your goal is to reproduce that formula.

Read the name on the ingredient you own

A similar name can be misleading.

Plain guar gum and Guar Hydroxypropyltrimonium Chloride both have “guar” in the name. The second is a modified, positively charged conditioning ingredient. It brings different properties to a formula. Having one on the shelf doesn’t make it a substitute for the other.

Even an identical INCI name may leave a grade question to answer. Xanthan grades can differ in clarity and flow behavior. HEC grades can have different viscosity specifications.

So, if a formula specifies a grade, keep that detail with the ingredient name when you check your supplies. Ask the supplier for the technical sheet if the label doesn’t tell you enough.

You may discover that you already have the right material. You may find that you have the same general ingredient in a different grade. Those are much more useful answers than “they’re both gums.”

There is no percentage that converts every thickener into another

If the formula uses 0.30% of one material, that number tells us how much of that material the formulator used. It doesn’t establish the amount needed for a different one.

Two thickeners might produce a similar-looking consistency at different concentrations. They may still differ during spreading or when lifted from the container.

A study of thickened alcohol-based hand rubs illustrates the problem. The researchers examined spreading and run-off as well as the way samples formed threads. Several materials provided acceptable spreading, but they didn’t behave alike in every test. These were alcohol-based systems, so their results aren’t substitution instructions for our lotions. They do show why matching one quality leaves other qualities to check.

For an alternative ingredient, look for a use level supported by its technical information in a relevant formula. Then review the other ingredients and preparation instructions. A general usage range is a starting point for that review, rather than a conversion chart.

If the change requires a different amount, recalculate the complete formula. Keep the total at 100% and record exactly what changed.

Check whether you’re replacing a powder or a blend

The product sold as a thickener may contain more than the thickening ingredient.

Some synthetic thickening systems are supplied with other components used in their manufacture, while other products are concentrated powders. Manufacturer information describes both forms.

Read the full composition before replacing one with another. Otherwise, you may remove ingredients from the formula without realizing they were there.

Here’s a made-up example to show the arithmetic. Imagine a supplied blend containing 25% of a particular thickener. Using 2 g of that blend contributes 0.5 g of the thickener and 1.5 g of its other ingredients.

Replacing those 2 g with 2 g of pure thickener would give four times the thickener and remove the other components. Even replacing it with 0.5 g would still leave those other components to account for.

That calculation only describes the hypothetical blend. With a real product, we need the supplier’s composition and guidance. It doesn’t provide a way to convert between different gums or polymers.

Keep a record of the changed formula

Once you substitute an ingredient, write down the full revised formula and its preparation method. Keep the original available so you can see what changed.

Be specific in your notes. “Used a different gum” won’t tell you much several months later. The ingredient name, grade, supplier and percentage give you a usable record.

The original formula’s testing also needs to be kept in context. It describes the original product. A changed formula needs its own evaluation for physical stability and microbial protection. FDA’s cosmetic testing guidance discusses the use of existing safety information and the possible need for additional testing of ingredients and finished products.

For someone making a product at home, that can sound like a lot to consider for a small substitution. It’s also a reason to research the change before weighing the ingredients. If the available information doesn’t support the replacement, you can keep the original ingredient or choose a formula designed for the material you own.

Use the comparisons to expand your choices

November’s demonstrations will give us a chance to become more familiar with several ingredients. That familiarity can help us recognize which ones deserve a closer look when changing a formula.

A substitution can be worthwhile even if it gives a somewhat different product. The important question is whether the change is acceptable for what you’re making and supported by the information available.

When you find a formula that uses a thickener you don’t own, begin with the ingredient’s purpose and the details of the material on your shelf. You’ll have a better basis for deciding whether to adapt the formula or keep looking.

Have you ever substituted a thickener and ended up with a product you preferred? What changed?