Henna and hair dye: what is safe to mix and what is not
Pure henna vs compound and "black henna", why henna and chemical dye or bleach can clash, the strand and skin tests to do first, and how to switch between them.
Written by the Glowpedia team · not yet reviewed by our dermatologist
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Henna is one of the oldest hair colors in the world, and many people love it for its shine and its natural look. Problems usually start when henna meets chemical dye, bleach or perms, or when the product sold as "henna" is not pure henna at all.
Quick answer: Pure henna (powder from the Lawsonia inermis plant) is approved as a hair dye and can usually go over old chemical color. Chemical dye, bleach, perms or relaxers over henna are riskier, especially if the henna contains hidden extras such as metal salts. "Black henna" often contains PPD, a dye that can cause serious skin allergies. Always do a strand test and a skin test first.
What is henna?
Henna is a powder made from the dried leaves of a plant. Mixed with water, it stains the outer layer of hair a brown, orange-brown or reddish-brown shade. It builds up slowly, and repeated use may darken hair gradually. The US Food and Drug Administration (FDA) says henna is approved only as a hair dye. It is not approved to be put directly on skin, including for mehndi (henna body art).
Types of "henna"
Not everything sold as henna is the same. Read the ingredient list, and be careful with products that give a color henna cannot make on its own, such as black or blue.
| Type | What's in it | Main risk |
|---|---|---|
| Pure henna | Only henna leaf powder | Generally low risk. Pure henna allergy is reported but very rare. |
| Henna with plant powders | Henna plus indigo (for brown or black shades) or cassia (for conditioning) | Same as above if the powders are pure. |
| "Compound" or "progressive" henna | Henna plus other ingredients, which may include metal salts or synthetic dyes, sometimes not listed | Can clash with chemical services and may trigger allergy. |
| "Black henna" | Often henna with PPD, a coal-tar hair dye ingredient | Serious skin reactions, including blisters and scarring. |
The FDA says the extra ingredient used to make "black henna" is often PPD (p-phenylenediamine). By law, PPD is not allowed in cosmetics applied to the skin. Hair dyes with PPD must carry a caution and instructions for a skin test.
Why henna and chemical color can clash
- Metal salts. Some hairdressers warn that products with metal salts can react with the hydrogen peroxide in bleach and many permanent dyes. They describe heat, a strong smell, odd colors or breakage. Because "natural" products do not always list these extras, you cannot be sure from the label.
- Henna coats the hair. Even pure henna can make the result of chemical color unpredictable, because it sits on the hair like a layer.
- Lightening is difficult. Bleaching hair that has been colored with henna can be hard to do evenly.
- Allergy risk. Black henna tattoos contain a lot of PPD, and having one may raise your chance of reacting to later hair dye that contains PPD.
Two tests to do first
1. A skin test for allergy. FDA advises a patch test every time you dye your hair, even if you have used the same product before. DermNet describes mixing the dye as directed and applying a small amount behind the ear or on the inner elbow, leaving it uncovered for 48–72 hours. Redness, swelling, blistering or itching means you should not use that dye. A skin test can also miss an allergy, so a clear result does not prove you are safe.
2. A strand test for the hair. The NHS advises testing dye on a strand of hair at least 48 hours before the full application. This also shows you the color. If you have used henna or are not sure, ask your colorist to test for metal salts before chemical work. Watch for heat, smoke, odd smells, color changes or hair that feels weak.
Switching safely
- From chemical dye to pure henna: Usually fine. Do a strand test, and expect the color to build up over several uses.
- From henna to chemical dye or bleach: Tell your colorist, do a strand test, and consider waiting until the henna has grown out or been trimmed. The FDA also advises waiting at least 14 days after bleaching, relaxing or perming before dyeing.
- Perms and relaxers after henna: Higher risk. Use a professional, and do a strand test.
- Box dye over henna: Not recommended without a test.
If you are pregnant or breastfeeding, ask your doctor or midwife about hair dye and chemical treatments before using them.
Caring for henna-colored hair
Henna can leave hair feeling stiff or dry, so use a moisturizing conditioner or hair mask after rinsing. Henna may fade or change if you color over it, so see color-treated hair for general care tips. If your hair is already dry or breaking, see dry and damaged hair.
How long does henna take to show its color?
Henna color often keeps deepening for a day or two after you rinse it out, so judge the shade after a day or two. It fades gradually over time.
When to see a doctor
- Itching, burning, redness, blisters or swelling on the scalp, face, eyelids or neck after henna or dye. Symptoms can take up to 72 hours to show.
- A rash that spreads, or swelling of the eyes or face. Contact a doctor promptly.
- Swelling of the lips, mouth, throat or tongue, or trouble breathing. This is an emergency: call your local emergency number.
- Blisters on skin after a "black henna" tattoo. A dermatologist can confirm an allergy and test safely.
If a dye mixture heats up, smokes or smells strongly on your hair, rinse it out right away with plenty of lukewarm water, and see a professional.
FAQ
Is henna good for hair health?
It coats the hair surface and adds shine, but it can feel dry. Condition well. See itchy, sensitive scalp if your scalp reacts.
Can henna cover gray hair?
Henna usually turns gray hair orange or red. Some people use indigo after henna for brown or black shades.
How long should I wait before using chemical dye?
The safest approach is to wait until the henna has grown out or been cut, or at least to do a strand test and talk to your colorist.
Is "black henna" safe on skin?
No. FDA has received reports of injuries from products marketed as black henna. Avoid it, especially for children.
Can I be allergic to hair dye I used before?
Yes. DermNet notes that reactions can get stronger with each exposure, so do a skin test every time.
Sources
- Temporary Tattoos, Henna/Mehndi, and "Black Henna": Fact Sheet (US Food and Drug Administration)
- Hair Dyes (US Food and Drug Administration)
- Hair dye reactions (NHS)
- Paraphenylenediamine and hair dye contact allergy (DermNet)