Paste the ingredient list off any bottle. We'll tell you what each one does, flag what's worth a second look, and show you the source — so you can decide for yourself.
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A preservative that works by slowly releasing small amounts of formaldehyde.
Formaldehyde is classified by IARC as carcinogenic to humans (Group 1). The EU requires products releasing over 0.001% to carry a formaldehyde warning label.
Preservative in the same family as DMDM hydantoin.
Releases formaldehyde over time. Same IARC Group 1 classification applies to the released formaldehyde.
Antimicrobial preservative.
A formaldehyde donor. Also a comparatively common contact allergen.
Preservative.
Releases formaldehyde. Banned from cosmetics in the EU.
The active in lye relaxers. Permanently breaks the disulfide bonds that give hair its curl.
A 2022 NIH Sister Study analysis found women who used chemical hair straighteners frequently had a higher incidence of uterine cancer than non-users. Also causes scalp burns at high concentration.
Source: Chang et al., J Natl Cancer Inst (2022) — NIH Sister Study, hair straighteners & uterine cancer
The active in most no-lye relaxers, used with calcium hydroxide.
"No-lye" is not the same as gentle. Same category of straightener studied in the NIH Sister Study association with uterine cancer.
Source: Chang et al., J Natl Cancer Inst (2022) — NIH Sister Study, hair straighteners & uterine cancer
A solvent used to make fragrance linger. Often not listed by name — it hides inside "fragrance" or "parfum".
Phthalates are studied as endocrine disruptors. Silent Spring Institute found products marketed to Black women more likely to contain endocrine-disrupting chemicals.
A legal catch-all. A single "fragrance" listing can cover dozens of undisclosed compounds, including phthalates.
Not inherently harmful, but it is the main way phthalates enter a product without appearing on the label. Worth avoiding if you are trying to avoid them.
Preservative that prevents mold and bacteria.
The EU capped propyl- and butylparaben at 0.14% and banned them in leave-on products for the nappy area, citing endocrine-activity uncertainty. Considered safe by US regulators at used levels — this is a judgment call, not a settled danger.
Source: EU Regulation 358/2014 & 1004/2014 — paraben restrictions
A strong detergent that produces heavy lather.
Strips natural oils, which textured hair can rarely spare. The ethoxylation process can also leave trace 1,4-dioxane, a manufacturing byproduct the FDA monitors.
A harsher detergent than SLES.
Effective at removing buildup but very stripping on coily and high-porosity hair. Fine occasionally as a clarifier; poor as a weekly shampoo.
A short-chain alcohol used to speed drying and thin a formula.
Evaporates fast and takes moisture with it. Position matters — near the end of the list is usually fine; in the top five it will dry your hair out.
A volatile silicone that gives instant slip and a silky feel.
The EU restricted D4 and D5 in wash-off cosmetics from 2020 over environmental persistence. On hair, it is a buildup risk without a strong cleanser.
Source: EU Regulation 2018/35 — D4/D5 siloxanes restricted in wash-off cosmetics
A non-water-soluble silicone that coats the strand to smooth and reduce frizz.
Not a health concern. It is a buildup concern — it needs a sulfate or clarifying wash to remove, and it can block moisture from getting in if it accumulates.
A petroleum-derived sealant.
Seals moisture in but adds none itself. Useless on dry hair, useful over a water-based leave-in. Not absorbed by the strand.
Pulls water from the air into your hair.
Excellent in normal and humid conditions. In very dry or cold air it can reverse and pull moisture out of the strand. Climate-dependent, not good or bad.
Small protein fragments that temporarily patch gaps in a damaged cuticle.
Genuinely strengthening for damaged or high-porosity hair. But too much without matching moisture causes protein overload — stiff, straw-like strands that snap. Alternate, don't stack.
One of the few oils that actually penetrates the hair shaft rather than sitting on it.
Reduces protein loss for many people. But it behaves like a protein for some — if your hair goes stiff and brittle with it, that is why. Often too heavy for low porosity.
A waxy, fatty alcohol used to soften and thicken conditioners.
Commonly avoided by mistake because of the word "alcohol". These are emollients — they moisturize and add slip. Nothing like drying alcohols.
A rich plant butter that seals and softens.
Excellent for coily, high-porosity, and dense hair. Can weigh down fine or low-porosity strands if used heavily.
A lightweight moisturizer and mild scalp soother.
Adds slip and hydration without weight. Works well for low porosity, where heavier butters tend to sit on top.
A gentle detangling conditioner. Despite the name, not a sulfate detergent.
Frequently avoided by mistake for containing "sulfate". It is one of the best slip agents available for detangling coily hair.
A thick, heavy sealing oil popular for edges and scalp.
Good sealant with real slip. No solid evidence it grows hair faster — the benefit is moisture retention and reduced breakage, which reads as growth.
A liquid wax whose structure is close to the scalp's own sebum.
Light, non-greasy, and well tolerated on the scalp. A good choice for fine or low-porosity hair that heavier oils overwhelm.
Provitamin B5. Absorbs into the strand and holds water there.
Adds moisture and elasticity without the stiffness of protein. Safe for people who react badly to protein.