Temporary, semi, demi, and permanent dye explained

A hair strand has three parts, and dye types are defined by how deep they reach.

The cuticle is the outside, made of overlapping scales like roof tiles. When it lies flat, hair looks shiny and feels smooth.

The cortex is the thick middle layer. This is where your natural pigment lives, and it is what gives hair its strength and its colour.

The medulla is a soft core in the centre, and it is not always present, especially in fine hair.

A dye that only coats the cuticle washes out fast and does almost no damage. A dye that opens the cuticle to reach the cortex lasts far longer but has to lift those scales to get in, which is where damage comes from. That single fact explains the whole ladder below.

Temporary colour includes sprays, chalks, wax, and colour mousses. The pigment sits on the outside of the cuticle and never enters the hair.

Lasts: one wash, sometimes less if you get caught in the rain.

Damage: essentially none, because nothing opens the cuticle.

Can it lighten? No. Nothing that sits on the surface can make hair lighter, so temporary colour only shows up properly on light or pre-lightened hair. On dark hair a bright temporary colour usually barely registers.

Best for: a party, a costume, testing a bold shade with zero commitment, or covering a small patch of grey between appointments. Be aware that it can transfer onto pillowcases and pale collars.

Semi-permanent colour uses small pigment molecules that slip under the edge of the cuticle and stain the outer layer. There is no ammonia and no developer (peroxide), so nothing is chemically changed inside the strand.

Lasts: roughly four to twelve washes. It fades gradually rather than growing out with a hard line, because it is washing away rather than sitting in the cortex.

Damage: very low. This is the gentlest option that still makes a real difference.

Can it lighten? No. Semi-permanent can only add tone or go darker.

Best for: trying a shade before you commit, refreshing faded colour, adding richness, and vivid fashion colours on pre-lightened hair. It is the honest way to test a direction without consequences.

Demi-permanent is the most underrated option. It mixes colour with a low-strength developer, which lifts the cuticle just enough to deposit pigment into the outer cortex.

Lasts: around twelve to twenty-four washes, usually six to eight weeks. It fades softly rather than leaving a sharp regrowth line.

Damage: low. There is a developer involved, but it is weak and there is normally no ammonia.

Can it lighten? Barely. It can shift tone and go darker, and it can blend grey, but it cannot meaningfully lift.

Best for: blending grey rather than fully covering it, toning brassiness, adding shine, going darker, and refreshing colour without committing to permanent. Most salon glosses and toners are demi-permanent. If you want a real change but hate the idea of a hard regrowth line, start here.

Permanent colour uses an alkaline agent (usually ammonia) to swell the cuticle open, plus a stronger developer. Once inside, small colourless molecules react with each other in the cortex and become large coloured molecules that are physically too big to wash back out.

Lasts: it does not wash out. It fades a little and it grows out, which produces a visible line at the roots after four to six weeks.

Damage: moderate. Forcing the cuticle open repeatedly is what makes long-term colouring rough on hair.

Can it lighten? Yes, usually one to three levels, though lifting and depositing at once has limits on dark hair.

Best for: full grey coverage, lasting colour, and going darker permanently. The main trade-off is commitment: you cannot simply wash it out if you dislike it, and removing it is harder than applying it was.

Bleach is not a dye. It is a lightener, and it works by opening the cuticle and chemically destroying your natural pigment inside the cortex. Nothing is added. Something is taken away.

This is why bleach is the harshest thing you can do to hair. It permanently removes pigment and weakens the internal structure, and hair does not repair itself, so the damage stays until it is cut off.

Bleach also lifts through a predictable sequence of warm stages: dark brown to red, then orange, then yellow, then pale yellow. That orange and yellow phase is not a mistake. It is the natural warm pigment being exposed, which is why toner exists as a separate step afterwards.

If you want to go significantly lighter than your natural colour, bleach is the only route. See our going blonde from dark hair guide for how to do it with the least harm.

A toner or gloss is usually a demi-permanent colour used to correct unwanted tone rather than change the level.

After lightening, hair is left somewhere on the yellow-to-orange range. A toner deposits the opposite colour to cancel it, using basic colour theory: purple cancels yellow, blue cancels orange, and green cancels red.

A gloss does the same job but is often more about shine and richness than correction. Both are low-damage, both wash out over four to six weeks, and both are the reason salon colour looks more finished than most home colour. If your colour is the right level but the wrong tone, a toner is almost always the answer, not a full recolour.

Match the type to the goal, not to how dramatic you want to sound.

Testing an idea: semi-permanent. It washes out and costs you nothing but time.

Going darker: demi-permanent if you might change your mind, permanent if you are certain.

Blending a little grey: demi-permanent, which softens grey into a highlight-like blend.

Covering grey fully: permanent, because it is the only type that reliably holds on resistant grey hair.

Fixing brassiness: a toner or gloss, not a new colour.

Going lighter than your natural colour: bleach, then a toner.

A useful habit: always choose the gentlest type that achieves the goal. People routinely reach for permanent colour when a demi would have done the job with far less damage.

You can layer these, but order matters.

Putting a semi or demi over permanent colour is fine and is how most people refresh faded ends. Putting permanent colour over a build-up of old permanent colour is where hair gets flat and dark, because pigment stacks up on the ends. Ask for colour to be applied to the roots first, then pulled through for only the last few minutes.

Do not bleach hair that already has a lot of permanent colour on it without professional advice. Bleach lifts natural pigment much more predictably than artificial pigment, and the result can be patchy.

Never mix two products from different brands into one bowl, and never apply colour over freshly relaxed or permed hair. The AAD advises doing only one chemical service at a time, and if you want both, perm or relax first and wait about two weeks before colouring.

Plant dyes sit outside the categories above and behave differently enough to need their own note.

Pure henna stains the outside of the hair with a red-orange pigment. It coats the strand rather than lifting it, so it cannot lighten, and on dark hair it usually shows only as a warm tint in sunlight. It is generally low risk and can make hair feel thicker, because it builds up a layer on the surface.

The complication is that it is close to permanent. Henna does not wash out and it resists being lifted, which is why it limits what you can do later.

Compound henna is a different matter. Products sold as black henna or fast-acting henna can contain added chemicals, including PPD, sometimes at high concentrations. These are the ones associated with serious skin reactions, and they can also react unpredictably with bleach.

Always disclose any henna use to a colourist, even from years ago, and expect a strand test before any lightening. "Natural" on a label does not mean low risk, which our allergy and patch testing guide covers in full.

Real-world timing is shorter than the box suggests, because it depends on how often you wash and how porous your hair is.

Temporary: one wash.

Semi-permanent: four to twelve washes, so two to four weeks for most people.

Demi-permanent: twelve to twenty-four washes, about six to eight weeks.

Permanent: does not wash out, roots visible in four to six weeks.

Toner: four to six weeks, often less on very porous hair.

Porous hair, which includes anything previously bleached, grabs colour fast and loses it fast, so expect the shorter end of every range. Washing less often and using cooler water genuinely extends all of these, which our colour care and fading guide covers in detail.