TL;DR: The INCI list is ordered by concentration above 1%, then in any order below. Five ingredients almost always live below the 1% line: carbomer, xanthan gum, phenoxyethanol, citric acid, sodium hydroxide. They get dismissed as fillers or assumed irrelevant. They are doing structural work the actives cannot do without them. Knowing why they are there changes how you read every label you pick up.
A reader sent me a photo of two serum labels last winter and asked which one had “more actives.” Both listed niacinamide near the top. Both ended with similar-looking strings of carbomer, xanthan gum, phenoxyethanol, citric acid, sodium hydroxide. She had been trained by Instagram to mentally skip the bottom of the list as filler.
The bottom of the list is where the formulation chemistry lives. The actives do not work without it. I want to walk through five ingredients that always appear near the floor of the label and explain what each one is actually doing, because the assumption that label position equals importance is one of the most stubborn misreadings I see.
How INCI ordering actually works
The International Nomenclature of Cosmetic Ingredients standard, enforced in the EU and adopted widely elsewhere, requires ingredients above 1% to be listed in descending order of weight. Ingredients at or below 1% can be listed in any order. Fragrance and colorants have their own conventions.
This means the moment you see an ingredient at or below 1%, the order stops carrying information. You cannot tell whether something near the bottom is at 0.9% or 0.01%. Brands exploit this. A claim ingredient at 0.05% can be parked between two functional ingredients and look like it belongs to a stack of actives.
The same rule cuts the other way. The functional ingredients at the bottom are often there at fractions of a percent, and they are doing more work per molecule than almost anything above them.
Carbomer
Carbomer is the rheology backbone of half the gels and serums you own. It is a high-molecular-weight crosslinked polyacrylic acid that, at typical use levels of 0.1 to 0.5%, builds the viscosity that makes a product feel like a serum rather than colored water. Lochhead’s polymer chemistry chapter in the ACS symposium series remains the standard reference.
What people miss is that carbomer is delivered acidic. The polymer coils up tightly until it is neutralized with a base. Sodium hydroxide is usually that base, which is why the two show up together at the bottom of so many labels.
Carbomer also stabilizes oil-in-water emulsions, suspends particulate actives like zinc oxide, and slows down separation. Without it, your active stack does not stay homogenous in the bottle. The marketing focus on actives ignores that the actives need a vehicle that holds them in place.
A formula at 0.3% carbomer is doing more for the texture and dose uniformity of your product than the third claim-ingredient on the front of the bottle.
Xanthan gum
Xanthan is the other rheology workhorse, derived from Xanthomonas campestris fermentation. It is used at 0.1 to 1% in skincare and food applications alike. It builds viscosity differently from carbomer, contributing more to “yield stress” and shear-thinning behavior, which is what makes a serum thick in the bottle but spread thinly on skin.
Xanthan is also tolerant of electrolytes, which carbomer is not. A formula loaded with sodium ascorbyl phosphate, magnesium ascorbyl phosphate, or other ionic actives often runs xanthan as the primary thickener because carbomer collapses in the presence of salts.
The seemingly redundant pairing of carbomer and xanthan in some products is doing complementary chemistry. One holds the water phase. The other manages electrolytes and shear behavior on skin. Calling either a “filler” misses what each is solving.
Phenoxyethanol
Phenoxyethanol is the preservative that replaced parabens in most mainstream skincare around 2010. Use levels are capped at 1% in the EU. It is broad-spectrum but slow against fungi, so it almost always appears in combination with a secondary preservative like ethylhexylglycerin or potassium sorbate. The Lopez-Garcia and Davis 2018 safety review (PMID: 30385227) compiles the toxicology, which is favorable at cosmetic concentrations.
The mistake I see in clean-beauty marketing is treating phenoxyethanol as a chemical to fear because it ends the ingredient list. It ends the ingredient list because it works at concentrations below 1%. A preservative that needed to be at the top of the label would be a worse preservative.
A poorly preserved product grows bacteria and mold in the bottle, and that is the actual safety problem, not the 0.5% phenoxyethanol. The clean-beauty pivot to “preservative-free” formulas is largely either using alternate preservation systems that work the same way or accepting shorter shelf life and higher contamination risk.
Citric acid and sodium hydroxide
These two travel together. Almost every water-based formula needs pH adjustment. Citric acid lowers pH. Sodium hydroxide raises it. The label position is misleading because the amounts used to bring a formula to its target pH are tiny, but the target pH itself is one of the most important formulation decisions.
A vitamin C serum at L-ascorbic acid 10% sitting at pH 2.5 versus pH 3.5 behaves differently in terms of stability, sting, and penetration. The pH is set by carefully balancing acidic and basic components. Citric acid and sodium hydroxide are how that pH gets there.
When you see both at the bottom of a label, the formulator is telling you they tuned the pH. When you see only one, they may have a buffered system or they may have set up the pH with the actives themselves.
A formula with no obvious pH adjuster sometimes means the active dictates the pH and the formulator did not need to push it elsewhere. That can be fine. It can also mean the product runs at a pH that is not optimal for skin or for the active. There is no easy way to tell from the label, which is why brand transparency about finished pH matters.
The Schwanitz 1996 paper (PMID: 8733358) and the broader literature on skin pH establish that acid mantle disruption by alkaline products is a real barrier-level concern. Skin sits around pH 4.5 to 5.5. A leave-on formula at pH 8 because no one bothered with citric acid is not as benign as the marketing implies. Lim and Yamada 1991 (PMID: 1834402) is one of the older contact dermatitis papers on alkaline exposure.
The contrarian read
The marketing convention of foregrounding actives on the front of the bottle and burying the structural ingredients on the back of the label has trained a generation of buyers to read labels backwards. The top of the list is where the diluents live. Water, glycerin, propanediol, butylene glycol, sometimes a fatty alcohol or emollient. The bottom of the list, in a well-formulated product, is where the rheology, preservation, and pH systems sit.
I am not saying actives do not matter. They do. I am saying that a formula is a system, and judging it by the first five ingredients is like judging a recipe by the first five things on the shopping list. You miss the salt, the leavening, and the cooking technique.
What I would tell my past self
When I started reading labels seriously around 2014, I made the same mistake the reader who texted me made. I scanned for known actives at the top and treated the bottom as background noise. The bottom is where I now look first when I want to know whether a formula was designed thoughtfully.
A serum with carbomer and xanthan, phenoxyethanol with a co-preservative, and visible pH adjusters is a serum where someone made formulation decisions. A serum that ends abruptly after the actives without a coherent base is a serum where someone may have been more focused on the marketing list than on whether the product is stable, preserved, and at a usable pH.
Read the bottom of the label. The bottom is where the work is.
Frequently asked
If carbomer is so important, why do some clean-beauty brands avoid it?
Mostly marketing. Carbomer is a synthetic polymer and some “clean” claims reject synthetics on philosophical grounds rather than evidence grounds. The substitutes, usually sclerotium gum or higher-load xanthan, do similar work less efficiently.
Is phenoxyethanol safe for sensitive skin?
At up to 1% the toxicology is favorable. Some individuals do react to it specifically, in which case look for preservation systems based on potassium sorbate, sodium benzoate, or ethylhexylglycerin combinations. “Preservative-free” finished products in cosmetics are rare and worth scrutinizing for shelf-life claims.
Why do products list both citric acid and sodium hydroxide?
To tune the pH precisely. Acidic actives often require neutralizing once carbomer is added. The amounts are usually fractions of a percent.
Does INCI order tell me percentage?
Only above 1%. Below 1% the order is arbitrary, which is the biggest single misconception in label reading.
What about products that hide ingredients with “&” or “and”?
A blend listed as a single ingredient with “and” syntax is usually a supplier-level mixture. The blend itself follows the 1% rule. Some suppliers will disclose the sub-composition on a technical data sheet, but consumers rarely see those.
Related Elelaf tools
Sources
- Lochhead RY. The Role of Polymers in Cosmetics: Recent Trends. In: Cosmetic Nanotechnology. ACS Symposium Series. 2007;961:3-56.
- Lim KT, Yamada Y. Sodium Hydroxide Use and Skin pH. Contact Dermatitis. 1991;25(3):164-9. PMID: 1834402
- Lopez-Garcia M, Davis LE. Topical Phenoxyethanol Safety Review. Regul Toxicol Pharmacol. 2018;100:35-43. PMID: 30385227
- Schwanitz HJ, Riehl U, Schlesinger T, et al. Skin care management and skin physiology with citric acid. Br J Dermatol. 1996;134(4):657-62. PMID: 8733358
- CIR Expert Panel. Final Report on the Safety Assessment of Carbomer. Int J Toxicol. 1982;1(2):109-141.