Article updated on: August 19, 2026
Know What's in Your Hair Dye: A Guide for Health-Conscious Consumers
Are you concerned about the impact chemical hair dyes may have on your scalp and overall health? This guide is here to help you understand and avoid commonly used chemicals in hair color products. We'll walk you through eight ingredients frequently found in conventional hair dyes—like PPD, ammonia, and SLS—so you can check your own product's ingredient list and make safer, more informed choices. By choosing natural or certified organic hair colors, you can reduce your exposure to potentially harmful substances, maintain healthier hair, and enjoy greater peace of mind.
Your skin has tiny openings that allow substances, including chemicals, to be absorbed. In a study of caffeine absorption, the absorption rate constant through hair follicles was nearly ten times higher than through the outer layer of skin — though the authors note this route matters most in the first minutes after application.[1] With roughly 100,000 hair follicles on your scalp, it's worth considering what is in the hair color you use.
To help protect your health, we want to help you reduce potential risks. This article shares information on common chemicals found in hair dyes and the effects they can have. We've compiled a list of eight chemicals often found in hair color products to help you easily identify them on the ingredient list when choosing a hair dye. By being aware of these ingredients, you can make safer, more informed choices for your hair and scalp.
1. P-phenylenediamine (PPD)
PPD is short for para-phenylenediamine. It is used as a dye for dark color shades and is made from coal tar, a petroleum-derived chemical that includes benzene, naphthalene, phenols, aniline, and other chemicals. It is also used as a wood preservative, and contact with skin is best avoided.
PPD can cause reactions ranging from mild skin irritation to more severe allergic contact dermatitis.[2] Sensitive individuals may experience dermatitis — skin inflammation and irritation commonly called eczema. In more severe cases, there may be marked reddening and swelling on the scalp and the face. An allergy to PPD can result in widespread contact dermatitis, hives, and, in rare severe cases, anaphylaxis.
2. Hydrogen peroxide
Hydrogen peroxide is the developer — the liquid you mix into the color cream before applying it. It acts as the oxidizing agent, and its job is to dissolve the melanin already in your hair so that new pigment can take its place.
That reaction does not stop at the melanin. It also converts the cystine bonds that hold keratin together into cysteic acid, which leaves the fiber weaker and rougher than it was.[3] This is the single most consequential ingredient on this list — not because it is the most likely to irritate your skin, but because its effect on the hair itself accumulates with every application.
3. Ammonia
Ammonia raises the pH of the mixture to swell and lift the cuticle — the outer layer of overlapping scales — so that dye precursors can reach the cortex inside the shaft.
Ammonia can irritate the skin and eyes, and its smell is the reason salons need ventilation. The more lasting issue is what it does to the cuticle: once lifted and stripped, those scales do not grow back.
4. Ethanolamine (MEA)
Ethanolamine is used in many demi-permanent and "ammonia-free" hair colorants as a substitute for ammonia. It does the same job — raising pH to open the cuticle — but it has far less odor, which is why products containing it are often marketed as gentler.
Less smell does not mean less damage. A comparative study of keratin fibers found that ethanolamine produced structural damage comparable to ammonia, and in some measures greater, because it is less volatile and stays on the fiber longer.[4] "Ammonia-free" on a box is worth checking against the ingredient list.
5. DMDM hydantoin
DMDM hydantoin is a formaldehyde releaser. It slowly releases small amounts of formaldehyde as it breaks down in the product, which prevents mold, yeast and bacteria from growing. Formaldehyde is a known skin sensitizer, and DMDM hydantoin has come under scrutiny for that reason.
It appears more often in shampoos and conditioners than in the dye itself — so it is worth checking the products you use after coloring as well as the color.
6. SLS and SLES
Sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES) are strong detergents. They clean effectively, but they also strip the natural oils that keep hair pliable, and they lift color out faster than gentler surfactants do. SLS is the harsher of the two and is a recognized skin irritant at higher concentrations.
These are shampoo ingredients rather than dye ingredients, and they matter most in the days right after coloring. If your color fades quickly, your shampoo is a more likely cause than the dye.
7. Resorcinol
Resorcinol (benzene-1,3-diol) is a coupler used in permanent hair dye, skin peels and acne treatments. It reacts with the peroxide-containing developer to form the final shade.
It is a recognized skin sensitizer and can irritate the scalp. Studies in animals and in workers with high occupational exposure have also raised questions about effects on thyroid function, though the relevance of those findings to ordinary consumer use is still debated.
8. Methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI)
These two preservatives are often used together, in hair products, skin care and household cleaners, to stop fungi, yeast and bacteria from growing. Both are potent sensitizers: contact dermatitis from them rose sharply enough in the 2010s that regulators in Europe restricted their use in leave-on products.[5]
Sensitization tends to be permanent — once you react to them, you are likely to react again on future exposure.
Why any of this matters more than one application
Every chemical on this list is worth avoiding for its own reasons. But there is a bigger reason to care, and it has to do with how hair actually works.
Hair is dead tissue. Scalp hair grows about a centimeter a month and stays in its growing phase for two to six years before it sheds — which means the ends of shoulder-length hair have been on your head for roughly two and a half years. Everything done to that length in those years is still there.
There is no cell in the hair shaft to rebuild a cuticle once it has been stripped. No repair mechanism, no recovery over time. Whatever a treatment takes from the fiber stays taken until you cut that length off.
Color every four to six weeks and that is ten or more rounds a year, on hair that will stay on your head for several more. The question was never what one application does. It is what thirty do to the same strand.
An intact cuticle is also what makes hair reflect light evenly — the shine most people read as healthy is largely a surface that is still smooth. That is why avoiding damage is not a modest goal. Over the years a single hair is on your head, it is the only thing that was ever available.
What to do with this
We encourage you to choose hair colors with as few of these eight chemicals as possible. Opting for a natural hair color can be a safer choice, and selecting a certified organic hair color made with pesticide-free ingredients offers even greater peace of mind. Even switching for every few applications reduces the total.
Plant color works differently: pigment is carried in by water and stays on the outside of the fiber, so nothing has to be lifted or dissolved to make it work. It cannot lighten hair — that requires bleaching, and bleaching requires peroxide — but for anyone matching or deepening their own shade, that limitation costs nothing. See how plant color works →
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