Henna Safety: Who Should Not Use It
Natural henna has been applied to skin for thousands of years and is, for most people, straightforward. There are a small number of specific situations where it is not, and they are worth knowing before a cone is opened — particularly at family occasions, where henna is applied to a lot of people quickly and nobody is asked anything.
The one everyone knows: "black henna"
Products sold as "black henna" typically contain para-phenylenediamine, a hair-dye chemical never intended for direct skin application. On skin it can cause severe chemical burns, permanent scarring and lifelong sensitisation to a substance found in hair dyes and some textiles.
The tell is the claim itself: natural henna cannot stain jet black, and it cannot stain in an hour. Lawsone, henna's dye molecule, produces orange that deepens through reddish-brown to a dark brown over a day or two. A product promising black in under an hour is telling you it is not henna.
This is covered at length elsewhere on the site and it remains the single most important thing to get right.
The one almost nobody mentions: G6PD deficiency
This is the gap in most henna writing, and it matters because the populations where mehndi is a living tradition overlap heavily with the populations where the condition is common.
G6PD deficiency is an inherited enzyme condition affecting many millions of people worldwide, with higher prevalence in parts of South Asia, the Middle East, the Mediterranean and Africa. In people who have it, certain substances can trigger haemolysis — the breakdown of red blood cells.
Lawsone is among the substances documented as capable of triggering this, and the reported cases predominantly involve infants and young children, in whom henna applied to skin has been associated with severe haemolytic episodes requiring hospital treatment. The risk relates to the dye itself, not to any adulterant, so "natural henna" is not a reassurance here.
The practical position most guidance takes: do not apply henna to babies or very young children, and if there is any family history of G6PD deficiency or favism, that is a conversation with a doctor before henna is applied to a child at all. Screening is routine in newborns in some countries and not in others, so "we would know" is not always true.
If a child has had henna applied and becomes unwell — unusually pale, jaundiced, lethargic, or passing dark urine — that is a reason to seek medical attention promptly and to say that henna was applied. This is not a common outcome and it is a recognised one.
Pregnancy
Natural henna on skin is widely used during pregnancy and is generally regarded as low risk, but two points are worth making.
The first is that "black henna" is emphatically not in that category — PPD exposure is a bad idea for anyone and there is no reason to accept it while pregnant.
The second concerns essential oils. Terpene-rich oils are added to henna paste to help the stain develop, and the essential oil calculator's recommended ranges run from 1–3% for clove up to 3–8% for cajeput. Guidance on essential oil use in pregnancy varies by oil and is genuinely inconsistent across sources, so the sensible course is to ask a midwife or doctor rather than to rely on craft convention — and to keep concentrations at the low end if using them at all.
Skin reactions to genuine henna
True allergy to natural henna exists but is uncommon; most reported "henna allergies" turn out to be reactions to PPD in an adulterated product. Reactions to the added essential oils are more likely than reactions to the henna itself.
The standard precaution is a patch test: a small amount of the actual paste you intend to use, on an inconspicuous area, left for the usual time, and then watched for a day or two. Do it with the specific batch and the specific oil blend, since that is what changes between applications.
Henna also goes on intact skin only. Not on cuts, grazes, sunburn, eczema, or any broken or inflamed area — and not on anyone who is having an active skin flare where it would be applied.
Practical hygiene
Less dramatic than the above and worth doing:
- One cone per person where practical, and never a cone that has touched broken skin.
- Clean hands and a clean working surface. Paste is a wet organic mixture and is not sterile.
- Fresh paste. Henna paste is perishable; it is frozen for storage for a reason, and paste that has sat warm for days should be discarded rather than used.
- Know what is in it. If you did not mix it, you do not know the oils, the additives, or whether it is henna at all. Buying from a maker who lists ingredients is the whole of the defence.
What this page is and is not
This is general craft information, not medical advice, and it cannot assess an individual. The tools on this site compute paste ratios, oil concentrations, timings and quantities — craft arithmetic, nothing more.
Questions about G6PD deficiency, pregnancy, a child's suitability, or a skin reaction belong with a doctor or pharmacist. What this page is for is making sure those questions get asked at all, because the most common failure in henna safety is not a wrong decision — it is not knowing there was one to make.
Applying henna at events
Most of the above is easy to observe when you are mixing your own paste for one person. It gets harder at a wedding or a festival, where a queue forms, cones are shared, and nobody is asked anything.
A few habits make the difference without slowing things down. Ask, once, whether anyone has a skin condition or is applying for a young child. Keep the ingredient list to hand so you can answer what is in the paste. Do not apply over broken or inflamed skin even if asked to. And keep the paste you mixed separate from cones that arrived from elsewhere, so you always know which is which.
If someone brings their own cone and it promises a black stain, that is worth a conversation rather than a shrug — the person holding it usually does not know what PPD is, and the point of knowing is to be able to say so.
Reading a supplier
Since you cannot identify an adulterated paste by looking, the decision happens at purchase. Suppliers worth using state the ingredients, state the crop year of the powder, and do not make claims about black or instant results.
Body-art quality powder is sifted finely and sold for skin use; hair henna is a different product and often contains other plant dyes. Compound hennas — henna blended with indigo or other dyes for hair — are not for skin at all.
None of that is expensive. The whole of the defence is buying from someone who tells you what they sold you.