Rewritten 14 September 2026. The earlier version of this article said henna smells because its pigment oxidises, and that an acidic rinse neutralises the smell. Neither is quite right, and this version replaces both with what we actually know — including the part of the story we had left out.
What happened
A few years ago we were getting five to ten complaints a year about the smell of our hair colour. Not the usual “henna smells like hay” comment — that one we expect, and it is true. These were stronger: sour, sharp, off. The pouches had been on a pallet in a shipping container for about three months on the way from India, and then in a warehouse, and they were not sealed against air.
Our hypothesis was that the powder was oxidising in transit and storage, and that the smell was the result. We changed two things at once: every pouch is now vacuum sealed at the mill in India, at the point of milling, and we ship by air rather than by sea — about a week from the mill to our warehouse in Torrance, instead of about three months.
The complaints went from five to ten a year to close to zero, and have stayed there.
That is the whole reason this article exists. What follows is what the smell actually is, what we think was happening, and what we still cannot say.
What henna actually smells of
This part is measured. A 2016 study ran commercial henna samples from several countries through gas chromatography and identified 72 volatile compounds in the air above the powder. Two of the largest were (2E)-hexenal — the compound behind the smell of cut grass — and acetic acid, which is the smell of vinegar. The grassy note and the sour note that people describe are those two molecules, and they were present in every sample.
The same study found that samples differed considerably from one another, by origin and by batch. Which means that when someone says their henna smells stronger than last time, they may simply have a different harvest. Plant material varies, and this is one of the ways.
What we think happens as it ages — a hypothesis
This part is not measured, and we are labelling it as such. Milled leaf is mostly cellulose, but it carries oils and fats from the leaf, and fats exposed to air oxidise. Oxidised fats break down into short aldehydes and acids — the same families the study found in fresh henna, but more of them, and different ones. It is the same chemistry that turns cooking oil rancid. A pouch of powder with air in it, in a warm container, for three months, is a reasonable place for that to happen.
Two things follow if this is right. The smell gets sharper and more sour with age, which matches what customers were describing. And the pigment declines at the same time, because lawsone oxidises too — so an old, sour-smelling pouch is also a weaker one. We have not measured either change in our own powder. We are describing a mechanism that fits the observations, not a result.
What we changed, and what we can and cannot conclude
| Before | After | |
|---|---|---|
| Packaging | Sealed pouch, air inside | Vacuum sealed at the mill, at milling |
| Transit | Sea freight on pallets, about three months | Air freight, under a week |
| Smell complaints | Five to ten a year | Close to zero |
What we can say: we removed air from the pouch and cut the time in transit by more than ninety percent, and a specific kind of complaint stopped arriving. That is a real before-and-after, and we are confident the change in the powder is real.
What we cannot say: which of the two changes did it. We made them together, so the observation does not separate them. We also never measured the smell — complaints are a proxy, and most people who notice something do not write in. If we had run this as a test we would have changed one thing at a time and put a nose or an instrument on it. We did not; we were solving a problem, not running an experiment, and we would rather tell you that than dress it up.
The vacuum seal also has a consequence that has nothing to do with smell: sealed away from oxygen, the pouch keeps its colour strength for close to five years. Both dates are printed on it.
If your colour smells — what is normal
A grassy, hay-like smell in the pouch is the plant. That is the hexenal, and it is what fresh henna smells of. It is not a sign of anything.
A grassy smell on the hair for three to five days after colouring is normal too. Fine particles of leaf stay in the hair after rinsing, and they carry the smell until they wash out. Ordinary washing removes it over a few days.
If you would like it gone sooner, two things help with the particles, and we will be careful about how we describe them:
- Our Hair Treatment Powder — amla, reetha and shikakai — is a saponin wash that reads pH 3.2 to 3.5 on our meter. It lifts residual powder out of the hair, which is what a wash does. Whether it does anything to the smell beyond carrying the particles away, we have not tested. It carries no scent of its own to cover anything.
- A diluted apple-cider-vinegar rinse is something some customers use and report helps. Vinegar is itself acetic acid, so it is not neutralising anything — if it helps, it is by rinsing and by laying the cuticle flat. We have not tested it and we are passing the report on as a report.
When the smell means something is wrong
A musty, mouldy or fishy smell is not oxidation. It means the powder got damp and something grew in it. That can happen to any plant powder stored in a humid place after opening. Do not use it. An opened pouch should be closed tightly and kept dry; a sealed one has no air or moisture to start with.
A sharp, sour, vinegar-forward smell from a pouch that is still sealed is the one we used to hear about. If you get one from us now, we want to know, because it should not happen any more.
How to check a pouch
Every pouch carries the batch number, the date it was milled and the date it expires. The milling date tells you how old the leaf is. If the pouch is still under vacuum when it reaches you — hard and tight, not soft — it has not seen air since the mill. If it arrives soft, the seal has failed; tell us and we will replace it.
Reference
SPME-GC-MS analysis of commercial henna samples (Lawsonia inermis L.). Natural Product Research. 2016;30(3). doi:10.1080/14786419.2015.1055491 · PMID 26181510. Seventy-two volatiles identified across commercial samples of different origin; (2E)-hexenal and acetic acid among the major components; considerable variation between samples.
Our complaint figures are counts of customer messages, not measurements of the powder. The oxidation mechanism above is our working explanation, not a finding. Radico Colour Me Organic is a cosmetic product for external use on hair.