Ammonia-Free Grey Hair Colour: Why Plant-Based Is the Real Answer

If you have started reading labels, you have probably noticed how often the words "ammonia-free" appear on the shelf. It sounds reassuring. It suggests something kinder to your hair and your scalp. The trouble is that the phrase has become a marketing reflex rather than a real promise, and a colour can drop the ammonia while keeping plenty of other ingredients you were hoping to avoid. So before you choose your next box or book your next salon visit, it is worth understanding what "ammonia-free" actually rules out, what it quietly leaves in, and where the honest, gentle answer for covering grey really lies.

Why look for an ammonia-free colour in the first place?

Ammonia has a job in conventional colour: it lifts the outer layer of the hair, the cuticle, so that pigment and developer can push deep into the strand. It is effective, which is precisely why it has been used for decades. The downside is the part most of us already know from experience. That sharp, eye-watering smell. A scalp that tingles or stings, sometimes for hours afterwards. Hair that feels rougher and more porous over time, because forcing the cuticle open again and again leaves it less able to close.

For anyone with a sensitive scalp, thinning hair, or simply years of colouring behind them, wanting to step away from that is entirely reasonable. The instinct is sound. The problem is that the label you reach for next does not always deliver what you think it does.

"Ammonia-free" does not mean "natural"

This is the part the packaging rarely spells out. Removing ammonia does not turn a chemical colour into a natural one. In most ammonia-free formulas, the ammonia is simply swapped for a gentler-smelling alkaline agent, most commonly ethanolamine (MEA). It does the same job of opening the cuticle, just with less of the tell-tale odour, which is largely why it is used.

More importantly, the ingredients that actually create permanent colour are usually still there. Oxidative dyes such as PPD (paraphenylenediamine) and its relatives, plus a hydrogen peroxide developer, remain at the heart of the formula. These are the components most often linked to allergic reactions and scalp irritation, and dropping the ammonia does nothing to remove them. In other words, "ammonia-free" can be perfectly true on the label and still describe a colour that is chemical from start to finish.

None of this is sleight of hand on your part. The wording is technically accurate. It just answers a much narrower question than the one most people are really asking, which is: how do I colour my hair without harsh chemistry?

The only truly ammonia-free colour: 100% plant-based

If you want a colour with no ammonia, no MEA standing in for it, no PPD, no resorcinol and no peroxide, there is one honest route: plant-based hair colour made entirely from dye plants. This is colour built from ingredients such as henna, indigo, cassia and amla, each chosen for what it actually does to the fibre.

The mechanism is fundamentally different. Chemical colour works by opening the cuticle and depositing synthetic pigment inside. Plant pigments work the other way round: they bind to the surface of the hair and build up in successive layers, coating and reinforcing the strand rather than prising it open. That is why properly applied plant colour tends to leave hair feeling thicker, glossier and more substantial. You are adding to the fibre, not stripping it.

At Tresse Paris this is the whole point of what we make: a colour that is COSMOS Organic certified, made in France, free from ammonia, PPD, resorcinol and oxidants, gentle enough for a sensitive scalp, and genuinely good for the hair it sits on. It was also recognised at the Natexbio Challenge in 2024, which matters less than how your hair feels afterwards, but it is a fair sign we are not the only ones who think the approach holds up.

Covering grey without ammonia: the two-step method

Here is the honest bit, because it explains why so many people quietly conclude that "plant colour doesn't work." Very often it is not the plants that failed. It is the method, and specifically a step that other approaches forget or explain badly: preparing the fibre before the colour goes on.

Grey hair is a special case. It has lost its natural pigment, and its surface behaves differently from pigmented hair, which is exactly why grey is the strand that catches people out. Drop a single sachet of colour straight onto stubborn greys and you can get an uneven, washed-out result. That is the moment the disappointment sets in, and it is entirely avoidable.

Jung Ae, our co-founder, designed the Tresse method around this reality. It works in two steps:

• Step one prepares the fibre. The first sachet readies the hair so that grey strands can actually take and hold the pigment, instead of repelling it.
• Step two applies the colour. The second sachet delivers the pigment onto a fibre that is now genuinely ready to receive it, for far more even, lasting coverage.

There is one more detail that quietly makes or breaks the result: temperature. Plant pigments only release properly within a specific warmth range, so every Tresse pack includes a thermometer. It is a small thing that removes the guesswork, and it is the difference between "I think that's about right" and a result you can rely on every single time. We did not invent plant colour. We improved the experience of using it, so it actually delivers what the plants are capable of.

Used this way, plant colour covers grey hair beautifully, around 100% on darker shades. And it lasts, because the pigment is bound to the fibre rather than washed in and waiting to fade.

An honest word about shades

We would rather be straight with you than sell you a result we cannot deliver. Plant-based colour pulls warm, by its nature. That makes a lovely range achievable: chestnut, caramel, copper, golden tones, mocha and auburn all sit comfortably within what the plants can do.

What it cannot do is lighten. There is no honest ashy, cool or light blonde from plants, and nothing plant-based will lift your natural colour, because only chemistry can lighten hair. Plant colour deepens, revives and covers; it does not bleach. If a lighter or cooler result is what you are after, this simply is not the right tool, and we would rather tell you now than have you disappointed later.

In short

"Ammonia-free" is a genuine claim that answers a narrow question. It usually still means a chemical colour, with MEA in place of ammonia and the oxidative dyes left intact. The only way to colour your hair with no ammonia and no harsh chemistry at all is 100% plant-based colour. Cover your greys with a proper two-step method, mind the temperature, choose a warm shade, and you get gentle, reliable coverage that strengthens your hair rather than wearing it down.

Frequently asked questions

Does ammonia-free colour cover grey hair?

It depends entirely on what is in the bottle. A conventional ammonia-free colour relies on oxidative dyes and a developer, so it can cover grey, but it is still a chemical formula. A 100% plant-based colour covers grey too, around 100% on darker shades, provided you use the two-step method that prepares the fibre first. With grey hair in particular, that preparation step is what makes the coverage even and lasting.

Does ammonia-free mean chemical-free?

No. This is the most common misunderstanding. "Ammonia-free" only tells you that one specific ingredient has been left out, usually replaced by another alkaline agent such as MEA. The oxidative dyes (like PPD) and the peroxide developer are typically still present. If you want a colour with no harsh chemistry at all, look for one that is 100% plant-based, not merely ammonia-free.

Does ammonia-free plant colour last well?

Yes, and that surprises people. Because plant pigments bind to the fibre and build up in layers rather than being deposited inside an opened cuticle, the colour tends to hold well and fade gently rather than washing out abruptly. Coverage is most durable on darker shades, and the result actually improves with repeated applications as the pigment continues to coat and reinforce the strand.

Is plant-based colour suitable for a sensitive scalp?

It is one of the main reasons people switch. With no ammonia, no PPD, no resorcinol and no peroxide, plant colour avoids the ingredients most often behind scalp stinging and irritation. The plant pigments coat the hair rather than forcing the cuticle open, so the experience is gentler from start to finish. As with any colour, a sensitivity test before your first application is always sensible.

Can plant-based colour lighten my hair?

No, and any product that claims otherwise is not being honest with you. Plant colour deepens, revives and covers grey, but it cannot lift your natural shade. Only chemical bleaching can lighten hair. Plant-based colour pulls warm by nature, so chestnut, caramel, copper, auburn and similar tones are well within reach, while ashy, cool or light blonde results simply are not achievable this way.