Eighteen days after the retouch, the white band is already sitting along your parting. You sweep the hair to one side, that buys you two days, and then it shows again. The annual total is twelve to seventeen salon visits just to cover two centimetres of root, and at some point you type into a search box whether highlights solve this.
They do, in part, and for some people. What almost nobody does before answering is the calculation that actually decides it: how much grey you have, and where it is. That calculation comes before the choice of technique, not after it. When it gets skipped, the client leaves with well executed highlights that blended nothing, plus the wrong conclusion that “highlights don’t work on my hair”.
What shows at the root is not the grey. It is the difference
A fibre without pigment is transparent. What you read as white or silver is light passing through the strand and bouncing around inside it. On the depth scale colourists use, from 1 (black) to 10 (the lightest blonde), that strand behaves like a 9 or a 10.
If your base is a dark brown, say a level 4, the distance between the base and the new growth is five to six levels. That difference is visible with three millimetres of growth, which is around ten days, because hair grows on average one centimetre a month (a little under half an inch).
Now lighten the base to a 7 or an 8. The distance drops to one or two levels. The same white root needs far more growth before it becomes a visible line, and what used to show in ten days starts showing at six, eight, sometimes ten weeks.
That is all the technique does. It does not cover the grey: it takes the grey out of evidence by bringing the rest of the hair closer to the lightness the unpigmented fibre already has. Once you understand that, you stop asking which technique blends best and start asking how much tonal distance there is in your own case.
The calculation that comes first
The proportion of grey is not a general impression. On dark hair, thirty per cent grey looks like far more than it is, because every light strand against the dark pulls attention on its own.
The useful estimate is done by area, not for the whole head at once. Divide it in four: parting and front hairline, temples, crown, nape. In each one, how much of the mass is unpigmented. A very common result looks like this: seventy per cent at the temples, forty at the front, fifteen at the crown, almost nothing at the nape.
That distribution matters more than the total. Forty per cent spread evenly dilutes easily. Forty per cent concentrated at the front sits exactly where your face is, on the line you see in the mirror in the morning and the one overhead light hits first. Two different cases with the same number.
With trichoscopy this can be counted per square centimetre instead of estimated: how many unpigmented strands, in which region, and how thick they are compared with the pigmented ones right beside them.
Where highlights work, and where they stop working
| Proportion of grey | What highlights do | Interval between visits | Note |
|---|---|---|---|
| Up to 30%, scattered | Dilute well; the grey starts to read as a reflect | 10 to 14 weeks | The ideal scenario, and the cheapest over a year |
| 30% to 50%, scattered | Dilute well, with regular toning at home | 8 to 12 weeks | Needs tone maintenance between visits |
| 30% to 50%, concentrated at the front | Dilute little where it matters most | 6 to 8 weeks | Usually calls for partial coverage on that panel only |
| 50% to 70% | Require lifting the base close to blonde | 8 to 10 weeks | This has become a lightening project, not a blending one |
| Over 70% | Little left to dilute; most of the hair is already light | not applicable | Toned grey turns out better, and cheaper |
The bottom row is the one that surprises people, and it is where I disagree with what usually gets sold. There is an intuitive logic that says the more grey you have, the more highlights you need. It is the other way round. Above roughly seventy per cent, you are paying to lighten the pigmented minority up to the point the majority already sits at naturally. The shorter and gentler route is to accept the grey and treat it as a colour in its own right, with toning.
The technical detail that changes the quote
Bleach has nothing to do on a strand that no longer has pigment. All the chemical work happens on the pigmented strands, and those are the ones the product has to reach.
That has two practical consequences.
The first is that on a head with a lot of grey, the mass actually receiving lightening is small, and it has to climb a long way to meet the level of the white fibre. Lifting dark brown hair to an 8 or a 9 is technically blonde work, with the session time and the fibre wear that implies, even when the final result does not look blonde at all.
The second is that an unpigmented fibre takes toner differently. A tighter cuticle, uneven porosity, and no pigment of its own to compete with what you deposit. The same toning time that leaves the rest of the hair neutral can pull the greys towards violet, or towards a grey you did not choose. This is the most common cause of “it came out a strange shade on some strands only”.
Toning is part of the calculation, not an afterthought
Highlights on hair with grey do not hold on their own. An unpigmented fibre yellows with product residue, pollution, minerals in the water and the hair’s own oxidation. In practice that means a toning shampoo or mask at home, weekly or fortnightly, with shorter leave-on times than the packaging suggests.
People who skip that part watch the work age in three weeks and conclude the technique did not last. It did last. The tone is what slipped.
Where the scalp weighs on the decision
Full coverage colour touches the scalp every three or four weeks, twelve to seventeen times a year. Foiled highlights sit a few millimetres away from the root, and balayage does not touch it at all.
For anyone with seborrhoeic dermatitis, psoriasis or a history of irritation from dye, that difference in contact is a genuine technical argument, not an aesthetic preference. Going from fifteen annual contacts down to five changes the exposure.
And here is the boundary. If your reaction to dye goes beyond discomfort and turns into raised patches, swelling, blistering or broken skin, that is an appointment with a dermatologist, before any colour service. In the same way, sudden whitening in one localised patch, loss of pigment in the skin alongside the hair, or grey established before the age of 25 deserve medical investigation, because there are described clinical causes behind those pictures. No hairdresser, and no cosmetic trichologist, settles that diagnosis.
Three questions that decide before you book
How many salon visits a year do you want to make? Full coverage asks for twelve to seventeen. Well indicated highlights ask for four to six. If frequency is what bothers you, that line already answers the question.
Is your grey scattered, or concentrated at the front? Concentrated at the front, the most honest route is usually a mixed one: partial coverage on that panel only, highlights everywhere else. Nobody has to pick a single technique for the whole head.
Do you intend to go grey one day? If so, highlights are the ramp. They reduce the contrast straight away and turn a future transition of twelve to twenty four months of visible demarcation line into almost nothing.
If you would like to talk about your case
At Nelblack, in Tatuapé (East Zone of São Paulo, near the Carrão and Tatuapé metro stations), a conversation is enough to count the proportion of grey by area, look at the tonal distance between your base and your white fibre, and leave with the route defined: highlights, partial coverage at the front, or a combination of the two, with the retouch interval and the number of visits a year on the table. Colour and highlights start from that reading, not from a shade name.
If there is shedding, itching or flaking alongside the grey, the trichoscope hair assessment costs R$200 (Brazilian reais), credited in full towards your protocol, and you follow the trichoscopy on screen together with the professional as the images come up.
We are open Tuesday to Saturday, 9am to 6pm, by appointment. Tuesday is the day reserved for scalp therapy. Service in English is available.