Haircare is a slightly reassuring category, because most of what you use gets rinsed off within a couple of minutes. Shampoo has a short contact time and goes down the drain.
The exposures worth attention are the ones that stay: leave-in conditioners, styling products worn all day, and above all the salon services that involve heat, fumes, and hours of contact. That last group is where the meaningful risk in this category actually sits.
The short answer
Do not overthink shampoo — it rinses. Pay attention to leave-in and styling products. Take keratin and chemical straightening treatments seriously, because formaldehyde exposure there is real and well documented. Wash less often than you probably do.
Shampoo: lower stakes than the marketing suggests
The sulphate question
Sodium lauryl sulphate and sodium laureth sulphate are detergents. They clean efficiently, and for some people they clean too efficiently, stripping natural oils and leaving hair dry or the scalp irritated.
That is a performance and comfort issue rather than a safety one. Sulphates are not a health concern in a rinse-off product. If your hair is curly, coarse, colour-treated, or dry, a gentler surfactant will probably suit you better. If your hair is fine and oily, sulphates may be exactly right.
Note that “sulphate-free” shampoos still contain surfactants — just different ones. Nothing cleans without them.
What is worth avoiding
- Fragrance in leave-in products especially, and in shampoo if you have a sensitive scalp.
- Methylisothiazolinone (MI/MCI) — a significant sensitiser that caused a wave of contact allergy. Tolerable in rinse-off for most, best avoided in leave-in.
- Formaldehyde-releasing preservatives — DMDM hydantoin appears in a surprising number of shampoos.
- Undisclosed ethoxylated ingredients, where 1,4-dioxane can remain as a contaminant.
Salon treatments: the part that genuinely matters
If there is one thing in this article worth acting on, it is this.
Keratin smoothing and Brazilian blowout treatments work by sealing the hair with a resin, and many formulations release formaldehyde when heated with a flat iron. Occupational health investigations have repeatedly measured airborne formaldehyde above recommended limits in salons performing these services — including in products labelled formaldehyde-free, because the releasing compound is listed under another name such as methylene glycol or formalin.
Formaldehyde is a recognised human carcinogen and a strong respiratory irritant. The exposure is highest and most sustained for stylists, who perform these services repeatedly, but clients sitting through a multi-hour treatment in a poorly ventilated room are also exposed.
If you have these treatments done: ask specifically what the product releases when heated, insist on genuine ventilation, and consider that “formaldehyde-free” on the bottle is not a reliable claim in this particular product category.
Hair dye, in proportion
Permanent dye involves ammonia or an alkaliser to open the cuticle, peroxide to lift colour, and PPD or related compounds to develop it. PPD is a well-known contact allergen — which is exactly why every box instructs a patch test 48 hours ahead, and why skipping it is a genuinely bad idea.
The broader cancer-risk research on personal hair dye use is mixed and not conclusive, with the clearer occupational signal appearing among hairdressers with decades of daily exposure rather than among people colouring their hair periodically.
If you want to reduce exposure without stopping: highlights and balayage keep dye off the scalp, demi-permanent formulas skip ammonia, and henna is a genuine alternative provided it is pure henna rather than a compound henna adulterated with metallic salts or PPD.
Wash less
The simplest improvement in this category costs nothing and reduces every exposure at once.
Daily washing strips sebum, the scalp compensates by producing more, and you wash again. Extending the interval breaks that cycle for most people, though it takes a few weeks of transition.
Practical notes: focus shampoo on the scalp and let the runoff handle the lengths, condition the ends rather than the roots, and use dry shampoo sparingly — it absorbs oil but does not clean, and buildup causes its own scalp problems. Aerosol versions also raise the inhalation question that powders do not.
Heat is the other half of hair damage
Much of what gets blamed on shampoo ingredients is thermal damage. Flat irons and curling wands routinely run at temperatures that permanently alter the protein structure of hair.
Lower the temperature, use heat protectant, and let hair air-dry partway before blow-drying. This does more for hair condition than any ingredient swap.
Frequently asked questions
Is the “no-poo” method a good idea?
It suits some people and not others, largely depending on hair type and scalp oil production. The common baking soda and vinegar version is worth caution — baking soda is far too alkaline for the scalp and repeated use can damage the hair cuticle. A gentle conditioner-only wash is a safer version of the same idea.
Do silicones damage hair?
No, they coat it, which is usually the point — they add slip and reduce breakage. Non-water-soluble silicones can build up and need a clarifying wash occasionally. That is a maintenance consideration, not a safety one.
Does natural shampoo cause a transition period?
Often, yes — a few weeks of hair feeling heavier or waxier as oil production readjusts and any silicone buildup clears. A single clarifying wash before switching shortens it considerably.
Are scalp treatments and oils worth it?
For a dry or flaking scalp, sometimes. Be aware that tea tree and peppermint oils are common irritants at high concentrations, and that persistent flaking, itching, or hair loss is worth seeing a doctor about rather than treating with product.
Keep going
This is one section of the Non-Toxic Personal Care Guide, which also covers skincare labels, deodorant, and oral care.