Your friend used the same jar for two months and her hair started behaving differently. You bought the identical product, followed the same instructions, and three weeks later yours is heavy, has no movement, and the roots are oily before day two.
The conclusion almost everyone reaches is that the product is weak, or that your friend oversold it. It is far more likely that the product is doing exactly what it promises, on a different head of hair.
Here is the thesis: a word-of-mouth recommendation is a test with a single participant, and the variables that actually decide the outcome never make it into the conversation. When it works, it works by luck.
What a recommendation carries, and what it leaves out
Think about what crosses the café table when your friend tells you about the product: the name, the result she noticed, roughly how long it took.
Now what does not cross the table:
- how thick her individual strands are;
- how many chemical services her hair has had, and how long ago;
- its current porosity;
- the condition of her scalp;
- how hard the water is in her building;
- how often she washes;
- the other four products she uses in the same week, one of which may be what actually changed something.
That second list is what determines how a strand responds. All that survives the conversation is the name on the jar.
Four variables, none of them visible to the naked eye
Porosity: the strand either absorbs or repels
Hair that has never been chemically treated carries, on the surface of the cuticle, a lipid layer chemically bonded to the fibre: 18-methyleicosanoic acid, usually shortened to 18-MEA. That layer is why water beads up and runs off virgin hair.
Bleaching, permanent colour with ammonia, relaxing and straightening all work at an alkaline pH, and alkaline pH strips that layer away. The strand stops repelling water and starts absorbing it. That is what porosity is: the loss of the barrier that controlled what went in and what came out, not “holes in your hair”.
Same mask, two destinies. On low-porosity hair it sits on the surface and most of it goes down the drain when you rinse, which feels like nothing happened at all. On high-porosity hair it goes in, and it goes in fast: the hair is soft on day one and heavy by day five. The product is identical. The substrate is not.
Thickness: the same dose is not the same dose
Human hair diameter ranges, broadly, from 50 to 120 micrometres. That sounds like a small difference. It is not: the cross-sectional area of a 100-micrometre strand is about four times that of a 50-micrometre one, because area grows with the square of the diameter.
The practical consequence is about surface. For the same weight of hair, fine strands offer far more exposed surface, so the same dollop of product deposits more per gram. This is why a protein cream or a denser oil gives body to thick hair and flattens the movement out of fine hair on the very first application.
Previous chemical work: what is already in the strand limits what still fits
Recently bleached hair usually needs water and lipids before anything else. Hair coming off three months of weekly reconstruction ampoules gains nothing from more protein: it goes stiff, snaps where it bends, and its owner will swear the product “dried her hair out”.
Two friends can have the same length and the same shade and need opposite things, because their histories are different. That history does not show up in an Instagram photo, and it is not printed on the label.
The water coming out of your shower
Hard water carries calcium and magnesium. Those minerals deposit on the strand and compete with whatever you apply: the shampoo lathers less, the mask goes less far, cool blonde drifts warm on its own. Hardness varies by supply area and also building by building, depending on the water tank and the plumbing. In São Paulo, where most buildings store water in a rooftop or ground tank before it reaches your shower, your friend can live six blocks away and still be washing her hair in different water.
What can actually be checked before you buy
A trichoscope is a magnifying device that projects the scalp and the hair onto a screen, with a scale. It shows a lifted cuticle, thinning strands, flaking, the density of strands per square centimetre and the average diameter.
It is worth saying what it does not do: porosity does not come out of it as a number. It is estimated by combining what the image shows with the chemical history and how the hair behaves in water.
| Variable | How it is checked | What changes with the same product |
|---|---|---|
| Strand thickness | measured with the trichoscope | Fine: the standard dose weighs it down. Thick: the same dose feels like not enough |
| Porosity | cuticle image, history, wettability test | Low porosity: little absorption. High porosity: absorbs fast and saturates |
| Previous chemistry | consultation, reading the strand | Decides whether the hair needs water, lipids or protein, and what is already saturated |
| Water at home | hardness strip, lather and colour clues | Reduces the effect of everything and shifts blonde tones |
How to test a product without fooling yourself
One product at a time. Swapping shampoo, mask and leave-in in the same week makes it impossible to know what did what.
Six weeks of consistent use before you judge. Three applications tell you almost nothing about treating the fibre.
Everything else held constant: same washing frequency, same water temperature, same dryer.
And judge it on the second day after washing at home, never on salon day. What you feel getting out of the chair includes the application technique, the filtered water at the basin and the blow-dry. None of that comes in the jar.
What a friend’s recommendation is good for
It is genuinely useful for the experience of using the thing: whether the texture is pleasant, whether the scent bothers you, how long the bottle lasts, whether the price holds up month after month. That is consumer experience, and it transfers reasonably well from one person to another.
It is not useful for deciding on active ingredients, concentration or frequency. That part depends on your hair, and your hair was not part of the experiment.
When it is not a product problem at all
If what you have is hair loss with progressive thinning of the strands, bald patches, an area losing hair, persistent redness, pain, or thick flaking that comes back within days, no shelf is going to fix that, and no salon is authorised to diagnose. The route is an appointment with a dermatologist. Hair therapy cares for the scalp and tracks how things progress; it does not replace a medical diagnosis, and where there is a clinical sign the referral comes before any protocol.
If you would like to talk about your case
The trichoscope hair assessment costs R$200 (Brazilian reais), fully credited towards your protocol. You follow the assessment on the screen, alongside the professional, and see what is being measured: density, average diameter, the condition of the cuticle and of the scalp.
That reading is where the home care kit comes from, and it is curation rather than a shop window: what your hair needs now, in the order and at the frequency that make sense for it. We measure again during or at the last session and compare with the image from the first day. At no extra cost.
Tuesday to Saturday, 9am to 6pm, by appointment, in Tatuapé, in the East Zone of São Paulo, near the Carrão and Tatuapé metro stations. Tuesday is the day reserved for scalp therapy. We offer service in English.