How to compare shampoo ingredients, part by part

Before you start

The general method, matching names first and then reading position, is in how to compare ingredient lists, and the side-by-side comparison does the matching for you. A shampoo adds one shortcut: its list falls into a few parts with distinct jobs, so comparing part by part is quicker than comparing name by name.

Two illustrative shampoos

The two lists, part by part

1. The surfactant system

Start with the cleansers. Shampoos usually blend two to four surfactants: the first listed is the primary cleanser, at the highest concentration, and the next ones offset its shortcomings.⁵ Here both shampoos lead with an anionic cleanser, Sodium Laureth Sulfate in A and Sodium Cocoyl Isethionate in B¹, and both back it with the amphoteric Cocamidopropyl Betaine.² B adds a glucoside, a non-ionic cleanser³, from the family described as the mildest.⁷

So the useful comparison is by family, not by the word sulfate: B is sulfate-free, but it does not swap an anionic cleanser for a non-anionic one. Shampoo surfactant types sorts the names, and what sulfate-free means covers the replacements. Which shampoo cleans more strongly is a question about amounts, and neither list gives them.

2. Conditioning agents

Both carry a cationic polymer, the kind of ingredient shown in shampoo tests to improve combing and the feel of hair; in those tests, poor removability and build-up were the most striking weaknesses of cationic guar.⁴ A adds Dimethicone, the silicone that made two-in-one shampoos possible: the detergent washes away, and the silicone stays as a thin coating on the hair.⁷ B adds Panthenol, listed in the EU database as hair conditioning and antistatic.⁸ If you avoid silicones, this row is where the two lists part; silicones in hair products explains when they build up.

3. Preservatives and scent

In the EU, a shampoo may only be preserved with substances on Annex V, within their conditions.⁹ Shampoo is a rinse-off product, which matters here: some preservatives are allowed only in rinse-off products, and some have a higher limit there.

• Methylisothiazolinone, in A: Annex V, entry 57, rinse-off products only, up to 0.0015%.¹⁰ The EU cut it to that level in 2017 to address an increased incidence of allergies to it.¹¹
• Sodium Benzoate, in both: Annex V, entry 1, up to 2.5% in rinse-off products against 0.5% in leave-on ones, measured as benzoic acid.¹⁰
• Potassium Sorbate, in B: Annex V, entry 4, up to 0.6%, measured as sorbic acid.¹⁰

Scent works the same way. Fragrance allergens must be named on a rinse-off product above 0.01%, ten times the leave-on threshold¹², which is why A names Limonene and Linalool, Annex III, entries 88 and 84¹⁰, after Parfum. B lists no scent ingredient at all. A shampoo with Parfum that names no allergen can still contain one below that threshold, so a missing name is not proof that an allergen is absent. Fragrance-free vs unscented goes further.

What the comparison cannot settle

• Strength. Two lists with the same cleansers in the same order can still differ in how much of each they contain.
• Mildness. The US Cosmetic Ingredient Review attached the same condition, formulated to be non-irritating, to sulfates such as SLES and to isethionates alike¹³¹⁴: the formula decides, and a list does not show it.
• Your hair and scalp. A comparison shows differences, not a winner.

Paste both lists into the side-by-side comparison, or check one at a time in the shampoo ingredient checker. Neither result is a verdict on either shampoo.