Hair care is the one personal-care category where the active ingredients do real work on a substrate instead of sitting on skin. The hair surface carries an isoelectric point near 3.67, so at any practical shampoo pH it is negatively charged and adsorbs cations. That single fact organizes the whole ingredient list: conditioning agents must be cationic, cleansing agents must be chosen for how they behave around that charge, and restructuring actives work by cutting or reducing the disulfide bonds inside keratin. If you source for a hair-care brand, each of those three jobs maps to a different specification sheet. This guide walks through the numbers that actually change performance, so a price list becomes a comparison of chemistry, not names.

Start With the Chain Length, Not the Marketing Name

Most conditioning performance is decided before you open the drum: by the alkyl chain on the quaternary ammonium head and by the counterion behind it. A C12 quat such as dodecyltrimethylammonium chloride (DTAC, CAS 112-00-5) adsorbs fast and rinses fast; it is useful as an antistatic and antimicrobial additive, but a rinse-off conditioner built on it will feel thin and can sting eyes in baby formulations. Move to C16 and you get the industry workhorse: cetyltrimethylammonium chloride (CAS 112-02-7, C19H42ClN, MW about 320) is the "1631" generation quat, supplied as 25% or 50% solutions or as a powder, and it deposits enough to detangle without waxing down fine hair. At C22, substantivity jumps again. Behentrimonium chloride (CAS 17301-53-0, C25H54ClN, MW 404.16) is made from the behenic acid of rapeseed oil, melts onto the hair shaft during conditioning and detangles coarse, chemically damaged hair that a C16 product leaves rough. As a buyer, treat the three as different products with different price floors, not as interchangeable "quats".

The Counterion Is Part of the Product

Two suppliers can quote the same C22 quat and deliver materials that behave differently in the process room. The chloride salt, behentrimonium chloride, needs heat to dissolve cleanly; the methyl sulfate salt, behentrimonium methosulfate (BTMS, CAS 81646-13-1, MW 479.81), disperses in cold water, keeps formulas clearer, and carries a milder sensory profile, which is why premium "sulfate-free" conditioners specify BTMS 50 rather than the chloride. Bromide counterions belong elsewhere: cetyltrimethylammonium bromide (CTAB, CAS 57-09-0) is the right answer for pharmaceutical and laboratory work, and it is the standard template surfactant in gold nanoparticle synthesis, and a rinse-off cosmetic gains nothing from a bromide counterion. When you evaluate quotations, the first question is not the active percentage alone but the full identity: which counterion, which cut, what solvent system, and whether the quoted 70% or 80% solution basis matches the weight your tank receives.

Polyquats: Conditioning Without the Buildup

Where monomeric quats deposit and accumulate, polyquaterniums trade some softness for clean feel and process stability. Polyquaternium-10 (CAS 81859-24-7) is a quaternized hydroxyethyl cellulose ether, typically quoted with a viscosity grade such as 1000 mPa·s at 2%: it conditions lightly, keeps clear shampoos genuinely clear, and is forgiving in 2-in-1 systems where silicone must stay suspended. Polyquaternium-39 (CAS 25136-75-8) is a terpolymer of dimethyldiallylammonium chloride, acrylamide and acrylic acid, with higher charge density; it boosts deposition of other actives and doubles as a styling film former. The specification line to interrogate here is residual acrylamide: ask for the ppm figure on the certificate of analysis, because regulatory limits for that residue are set in finished-product terms and your formula budget has to absorb them.

Anionic Cleansers: Four Options Beyond SLES

Shampoo cleansing bases differ more than their foam looks suggest. Sodium isethionate chemistry is the backbone of syndet bars: the cocoyl isethionate ester that gives "soap-free" bars their dense, low-irritation lather is manufactured from sodium isethionate (CAS 1562-00-1, C2H5NaO4S, MW 148.11), so a bar manufacturer is really buying this intermediate plus an acylating step. In liquids, sodium lauroylsarcosinate (CAS 137-16-6, MW 293.38) carries the old "Gardol" pedigree: it keeps foaming in hard water and gives a distinct, slippery afterfeel, but it performs only at alkaline pH, so check that your fragrance and colorant packages tolerate the same window. Sodium C14-16 olefin sulfonate (CAS 68439-57-6) is the value choice: sulfonated straight from alpha-olefins, hard-water resistant, fully biodegradable, and noticeably cheaper per active kilogram, at the cost of being harsher on the eye area than the premium options. For sulfate-free and children's lines, sodium coco hydroxyethyl sulfonate (CAS 61789-32-0) delivers coconut-derived mildness with respectable foam, and cocamidopropyl betaine (CAS 61789-40-0) remains the amphoteric partner that thickens the system and steadies the foam across water hardness. Match the base to the claim, then negotiate on assay and water content, not on headline price.

Keratin Chemistry: Perms, Depilatories and the pH That Runs Them

The restructuring actives share one backbone and split on formulation logic. Thioglycolic acid (CAS 68-11-1, HS-CH2-COOH, MW 92.12) at 99% assay is the raw material; as its salt it reduces cystine disulfide bridges in keratin, and an alkaline wave holds the hair on a rod while the bonds reform. Acid-wave chemistry uses the glycerol ester instead: glyceryl monothioglycolate (CAS 30618-84-9, C5H10O4S, MW 166.2) works near neutral pH and smells milder, but it is a documented contact allergen and has been restricted or withdrawn in several markets, so confirm the regulatory status of your destination before quoting it. Depilatory products push the same chemistry further: calcium thioglycolate (CAS 814-71-1, MW 206.29) in a cream at roughly pH 12 destroys enough keratin for the hair to wipe away, and the calcium salt is preferred over sodium or potassium versions because it is less hygroscopic and keeps the cream phase stable. Regional caps matter here: the EU, for example, limits thioglycolic acid to 8% in waving products and 5% in depilatories, so over-formulating wastes money. Around all of this, hydrolyzed collagen (CAS 9007-34-5) supplies the film-forming repair claim; specify a molecular weight distribution rather than a single average number, because penetration and surface filming are performed by different fractions.

Two More Specification Lines Worth Arguing About

Anti-dandruff systems live and die on particle engineering. Zinc pyrithione (CAS 13463-41-7, C10H8N2O2S2Zn, MW 317.7) only works if it deposits on the scalp, and deposition follows particle size and the suspension system around it; a cheap fine-milled grade in the wrong base is money spent on nothing, and note that the EU no longer permits ZPT in cosmetics while US OTC monograph routes still do, so build market-specific formulas. Finally, a closing checklist for quat-rich formulations: confirm the active-content basis (solid, 25%, 50%, 80%), free amine ppm for odor stability, APHA color for clarity-sensitive shampoos, counterion identity, water content, and for polyquats the residual monomer certificate. Suppliers who answer those lines in one e-mail have actually run the batches you are about to buy.