Gel and Water-Gel Formulation: Choosing the Right Thickener
A gel looks like an entry level product and is in fact the format that most often fails stability testing. The reason is that a gel is almost entirely water with a small amount of a structuring polymer, so the polymer is doing all the work and any interaction that weakens it shows up immediately as a product that runs, separates or turns to liquid on the shelf.
What a Thickener Has to Do in a Gel
Four properties matter, and different polymers deliver them to different degrees:
- Viscosity at rest. What the consumer sees when the jar is opened.
- Yield stress. The force required to make the gel start flowing. This is what stops a gel running off a fingertip, and it is a different property from viscosity. A gel can be thick and still have almost no yield stress.
- Shear thinning. The gel should thin as it is rubbed in and recover afterwards, which is what makes application feel pleasant rather than stringy.
- Electrolyte and pH tolerance. The property that decides whether the gel survives contact with the actives, the preservative and the pH adjuster in the formula.
The Main Thickener Families
Carbomer. The industry default for a clear water gel. It gives excellent yield stress and a very clean, non-tacky feel. Two limitations decide most projects. It needs neutralisation, usually to pH 6 or above, which rules it out for acid products. And it is highly sensitive to electrolytes, so a gel with 2 per cent of a salt, a strong buffer or certain active salts will lose most of its viscosity.
Xanthan gum. A fermentation derived polysaccharide. Tolerant of electrolytes and of a wide pH range, and it gives a slightly slippery, more natural feel. It is also pseudoplastic and recovers well after shear. The drawback is that it can feel stringy at higher use levels and it is not fully clear in solution, so it produces a slightly hazy gel.
Cellulose derivatives. Hydroxyethylcellulose and similar grades give a smooth, soft gel with good electrolyte tolerance and a pleasant non-stringy feel. They are often the answer when carbomer fails on electrolytes and xanthan feels too slippery. The trade-off is a weaker yield stress, so the gel may be softer.
Synthetic associative thickeners. Acrylates based polymers that build viscosity through association rather than simple chain entanglement. They tolerate electrolytes well and give a very good skin feel at low use levels. They cost more and some require careful pH control, but for a difficult formula they often solve a problem no natural gum will.
Clay and silica. Used for matte, opaque or suspension gels. They build structure without dissolving, so they suit a gel that needs to suspend particles, but they can be drying and they settle if the yield stress is marginal.
Matching the Thickener to the Formula
Three questions decide the choice more reliably than any ingredient list:
- Does the formula contain electrolytes? Actives such as sodium ascorbyl phosphate, sodium hyaluronate, most preservatives and any pH buffer all contribute ions. If the answer is yes, carbomer alone will probably fail and a tolerant system is needed.
- What is the target pH? Below 5, carbomer cannot be neutralised and the practical options are xanthan, a cellulose derivative or a synthetic associative thickener designed for acid systems.
- Does the gel need to suspend anything? If there are beads, capsules or an insoluble active, the formula needs genuine yield stress, which narrows the options to carbomer, a clay system or a purpose designed suspending polymer.
Processing Mistakes That Ruin Gels
Gel manufacture is short and therefore unforgiving, because there is no emulsification step to smooth over a mistake.
- Adding powder too fast. Carbomer and xanthan both form lumps when dumped into water. The powder hydrates on the outside and the inside stays dry, and those lumps never fully dissolve. Dispersing slowly under high shear, or pre-wetting with a humectant, avoids it. A humectant pre-dispersion is the simplest reliable method.
- Neutralising before hydration is complete. Carbomer must be fully hydrated before the neutraliser is added. Neutralising early locks in a lower viscosity that cannot be recovered by adding more.
- Over-shearing after neutralisation. High shear on a neutralised carbomer gel permanently reduces viscosity. Mixing after neutralisation should be slow.
- Ignoring order of addition for electrolytes. Adding a salt after the gel is built collapses the structure. Where the formula allows, hydrating the polymer in the water phase before the electrolyte containing ingredients are added gives a much better result.
Preservation in a High Water Product
A gel is the most challenging format for preservation because it is almost entirely water with little oil or solids to reduce water activity. The challenge test panel is the same four organisms, and the mould is the usual failure point.
Two formula specific notes. First, some thickeners bind preservatives and reduce the free concentration. Carbomer and certain clays are known to do this, so a preservative level that passes in water may fail in a carbomer gel. Second, a pH dependent preservative system only works if the gel's pH is inside its effective range, which is another reason the pH decision drives the whole formula rather than just the sensory profile.
Appearance and the Clarity Question
A clear gel sells better in most markets because clarity reads as purity, and it is a genuine formulation constraint. Carbomer gives the clearest result once neutralised. Synthetic associative thickeners can also be clear. Xanthan and most clays produce haze, and a gel containing an oil soluble active or a fragrance will be hazy regardless.
Where clarity is required and the formula contains an oil, a solubiliser is needed rather than a thickener change. This is worth testing early, because a solubiliser changes the sensory profile and the preservation load, and discovering it after the formula is approved means starting the stability programme again.
Gels Developed With the Thickener Matched to the Formula
OEM COSMETICS ODM develops water gels, aqueous serums, gel cleansers and suspension gels on ISO 22716 and GMP certified lines, with electrolyte and pH tolerance screening, yield stress measurement and preservative challenge testing in the actual base. Send us your active list and target feel and we will tell you which thickener system will hold.
Talk to our team: WhatsApp +86 18709713948 · Email adon@oemcosmeticsodm.com · Website www.oemcosmeticsodm.com