Root Cause Investigation of "Stringy/Sticky" Makeup Removers: Thickener Selection and Formulation Stability

I. "Stringiness" is a Texture Defect, Not an Efficacy Feature

When pouring makeup remover onto a cotton pad, the liquid forms a thin string at the bottle opening that takes forever to break; or the dispensed makeup remover has an obviously thick texture that leaves a "clingy" feel when wiped on the face, and after use, the skin feels as if it's covered with a thin film.

These experiences—stringiness, stickiness, and clingy feel—are typically attributed by consumers to "poor quality" or "impure ingredients." However, in reality, they can almost 100% be traced back to thickener selection or dosage issues, and the resulting loss of formulation stability control.

For brand owners, this is a highly controllable formulation engineering problem: by selecting the right thickener, precisely controlling the concentration, and conducting thorough formulation stability validation, "stringiness" can be completely eliminated at the sample stage, rather than traced back after consumer complaints.

II. Why Do Makeup Removers Need Thickeners?

Pure aqueous micellar water theoretically has a viscosity close to water (about 1–5 mPa·s). When poured, the product flows like water, easily dripping off the cotton pad and making dosage control difficult. Thickeners are introduced to enhance the product experience across several dimensions:

• Controlled Dispensing: Moderate viscosity prevents the product from flowing away too quickly when poured onto a cotton pad, reducing waste.

• Smooth Wiping Feel: A lightweight gel texture can form a lubricating layer between the cotton pad and the skin, reducing friction-induced irritation.

• Visual Quality: Appropriate viscosity gives the product an "essence-like" feel, enhancing the consumer's perception of product value.

• Active Ingredient Suspension: Functional makeup removers containing plant extracts or microencapsulated particles require thickeners to prevent phase separation and sedimentation.

However, while thickeners bring the above benefits, they are also the root cause of "stringiness" and "stickiness" problems. The issue is not whether to use them or not, but which one to use, how much, and how.

III. The Rheological Root Cause of Stringiness: Long Flow vs. Short Flow

To understand the "stringiness" phenomenon, we must start with the core rheological concepts: Long Flow and Short Flow.

High-molecular-weight linear polymers (such as xanthan gum, hydroxyethyl cellulose, guar gum, etc.) exhibit high stringiness at high concentrations, corresponding to what is called "long flow" in formulation practice—the system forms threads or filaments when stretched. In contrast, "short flow" refers to systems whose overall rigidity comes from highly cross-linked rheology modifiers, exhibiting rapid breakage after stretching without leaving threads.

Carbomer is the classic representative of short-flow thickening systems—the cross-linked polymer network swells upon neutralization, forming a three-dimensional micro-gel network that significantly increases viscosity while maintaining a transparent texture. Upon application, it presents a "instant-spread, instant-break" refreshing feel without stringiness. For leave-on products, consumers universally prefer the short-flow experience.

These two concepts directly correspond to the two most common root causes of stringiness in makeup removers:

• Root Cause A: Using linear high-molecular-weight thickeners represented by xanthan gum and HEC (Hydroxyethylcellulose), which inherently possess "long flow" characteristics at high concentrations, making stringiness inevitable.

• Root Cause B: When using carbomer, improper dispersion or neutralization steps cause local polymer chain aggregation, forming uneven gel clumps that manifest as "dragging strings" on the cotton pad rather than uniform spreading.

IV. Dissecting the Stringiness Risk of Mainstream Thickeners

① Carbomer — Crisp When Dosage is Precise, Stringy When Operations Go Wrong

Carbomer is one of the most widely used thickeners in toner-type products, capable of increasing viscosity to tens of thousands of cP within a dosage range of 0.1–0.5%. Carbomer is a swellable rather than truly soluble polymer; its dispersion system is acidic at a pH of about 3; after neutralization to pH 6–10, the particles swell to about 1,000 times their initial volume, and viscosity increases dramatically due to charge repulsion effects.

Two Triggers for Stringiness:

Stringiness typically indicates incomplete dispersion or localized over-neutralization. Carbomer must be fully hydrated before the addition of alkali. If the neutralizing agent is added too quickly, it creates localized alkaline micro-zones, causing irreversible polymer aggregation and triggering stringiness. The correct approach is to pre-disperse in cold water first, wait 15 minutes for full hydration, and then slowly add the neutralizing agent under continuous stirring.

Additionally, carbomer is extremely sensitive to electrolytes: ions compress the electric double layer of the polymer chains, weakening their hydration capacity and causing severe viscosity loss. When the formulation contains electrolytes (such as certain active ingredients or salts), carbomer grades with high ion tolerance must be prioritized.

When a makeup remover formulation simultaneously contains common ingredients like phenoxyethanol (weakly acidic) and niacinamide (with electrolyte effects), the viscosity stability of standard Carbomer 940/980 systems is often difficult to maintain. After a period of storage, issues of "becoming increasingly thin" or "localized gelation" may arise, causing stringiness to worsen during use.

Selection Recommendation: 

For the makeup remover category, it is recommended to select electrolyte-resistant carbomers (such as Lubrizol Carbopol Ultrez 30) or modified acrylates copolymer (Acrylates/C10-30 Alkyl Acrylate Crosspolymer), the latter offering superior stability in surfactant systems. Carbopol Ultrez 30 can provide stable thickening across a broad pH range of 4.0–12.0, exhibiting higher ion tolerance in formulations containing electrolytes or acidic actives (such as alpha-hydroxy acids) while maintaining good skin feel.

② Xanthan Gum — Natural and Stable, but Obviously Stringy at High Concentrations

Xanthan gum is currently the most mainstream natural-origin thickener. Its advantages include: good tolerance to salts and high/low pH, stable viscosity at high temperatures, and excellent suspension performance, making it the most widely used natural-based thickener.

However, xanthan gum inherently possesses "long flow" rheological characteristics. Long flow describes the formation of strings or threads when the system is stretched—this is the typical characteristic of high-molecular-weight linear polymers (such as xanthan gum, HEC, and guar gum) at higher concentrations. Consumers universally prefer the short-flow experience for leave-on products.

In makeup remover formulations, xanthan gum dosage is recommended to be strictly controlled at 0.05–0.15%. Beyond 0.2%, stringiness becomes visible to the naked eye at room temperature; beyond 0.3%, the product's spreadability on the cotton pad significantly deteriorates, resulting in a "dragging" sensation.

The optimization strategy is to compound xanthan gum with carbomer or acrylates copolymer: use 0.05–0.08% xanthan gum to provide suspension stability, and 0.05–0.1% carbomer (or acrylates copolymer) to provide the main thickening framework. The "short flow" characteristics of carbomer are used to suppress xanthan gum's stringiness tendency, while also ensuring the formulation's electrolyte tolerance.

③ Hydroxyethylcellulose (HEC) — Good Stability, but Difficult Texture Management

Unlike carbomer, HEC builds viscosity through simple hydration without requiring alkali neutralization for activation, making it more friendly to formulations with predetermined pH targets. Compared to xanthan gum, HEC produces a cleaner, less stringy gel texture with less resistance during spreading, and can balance visual effects with functionality in transparent formulations.

However, HEC is also a linear high-molecular-weight polymer. When usage exceeds 0.5%, the "long flow" stringiness phenomenon begins to appear. In cleansing product systems, the interaction between HEC and anionic surfactants may form complexes at specific concentrations, causing abnormally high viscosity. This is also one of the root causes of poor batch stability and the "becomes thicker over time" issue.

Recommended Dosage: In makeup remover systems, HEC used alone should be controlled within 0.2–0.4%; when compounded with acrylates copolymer, the respective dosages can be further reduced while achieving a shorter flow texture.

V. Temperature Stability: Troubleshooting Thickening System Hazards

Another common trigger scenario for stringiness/stickiness issues is the loss of formulation stability control after temperature changes. Below are the three most common temperature stability failure modes for makeup remover thickening systems:

Failure Mode	Trigger Condition	Affected Thickeners	Symptoms
High-Temperature Viscosity Drop	Summer warehousing (40°C+)	Carbomer (relatively stable at neutral pH, but network relaxes at extreme high temperatures)	Product becomes thinner; faster flow rate when poured.
Low-Temperature Gelation / Increased Stringiness	Winter transport (<5°C)	Xanthan Gum (double-helix structure strengthens at low temperatures, stringiness increases)	Product becomes thicker; stringiness significantly worsens.
Sudden Viscosity Collapse After Electrolyte Shock	Improper sequencing of active ingredient addition	Unmodified standard Carbomer 940	System collapses after adding niacinamide/preservatives; changes from gel to clear liquid overnight.

Conclusion: Formulation Stability is the Core Competitiveness of OEM Factories

Stringiness and stickiness may seem like minor issues, but they reflect the overall rigor of the formulation system design. The fact that one batch has no issues does not mean it will remain stable under different climate conditions and transportation environments.

From an industry trend perspective, associative thickening systems (Associative Crosspolymers synergistically thickening with anionic surfactants) have become the mainstream direction for cleansing formulations. Meanwhile, the functional transformation—from simple thickening to precise rheology modification control—is becoming the core technical barrier in high-end makeup remover formulation.

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