Hair Dye Allergy: PPD, Patch Tests and the Kala Mehndi Danger

Hair dye allergy is most often caused by paraphenylenediamine (PPD), a chemical present in many permanent and some semi-permanent hair dyes, particularly darker shades, and in high amounts in black henna, often sold in India as kala mehndi. A reaction usually shows up as itching, burning, redness, swelling or blisters on the scalp, hairline, ears, eyelids, face or neck, and the NHS notes symptoms can take up to 72 hours to appear.

Hair colouring is extremely common in India, from covering early grey hair to festival and wedding mehndi. Knowing how to dye safely can prevent painful reactions and lifelong allergy.

What is PPD and why does it cause allergy?

PPD is a colourless chemical that becomes a dye when mixed with a developer (oxidiser). That is why most permanent dyes come as two bottles or tubes. DermNet explains that the partly oxidised form of PPD is what can trigger allergic contact dermatitis.

Key facts from DermNet:

• Darker shades of dye contain higher concentrations of PPD than lighter shades.
• Allergy is more common in people with skin of colour, likely because they more often use darker dyes.
• The first exposure may cause no symptoms. Later exposures can cause faster, more severe and longer lasting reactions.
• After a reaction, lifelong sensitisation to PPD is likely.

What does a hair dye reaction look like?

According to the NHS and DermNet, reactions range from mild to severe:

Mild

• Stinging, burning or itching of the scalp
• A dry, itchy rash on the upper eyelids or the rims of the ears
• Dryness, tightness or soreness

More severe

• Marked redness, swelling and blistering of the scalp, eyelids, face and neck
• Oozing and crusting
• Rash spreading to other parts of the body

On brown skin, the NHS notes that a rash may look darker brown, purple or grey rather than red, and may be harder to see. DermNet adds that the dermatitis can leave behind dark marks, light patches or occasionally scarring.

Emergency signs

Call for emergency help if there is:

• Sudden swelling of the lips, mouth, tongue or throat
• Difficulty breathing or swallowing
• Blue, grey or pale skin, lips or tongue
• Sudden confusion, drowsiness, dizziness or fainting

The NHS says severe allergic reactions (anaphylaxis) to hair dye are rare, but they need immediate treatment.

What is the danger of kala mehndi and black henna?

Pure henna, from the plant Lawsonia inermis, gives an orange to reddish brown stain and rarely causes allergy. Black henna is different. To make the colour darker and faster, PPD is often added, sometimes in high amounts.

• The NHS notes that black henna tattoo pastes contain high levels of PPD and that having had a black henna tattoo increases your risk of an allergic reaction to hair dye later.
• DermNet describes black temporary tattoos causing intense blistering at the tattoo site within one to two days.
• A case reported in the Indian Journal of Dermatology, Venereology and Leprology describes a young man in India who developed an itchy, blistering rash after a temporary black henna tattoo, linked to prior sensitisation to PPD.

The risk in India is that “kala mehndi” is sold both for hair and for body art, often without clear labelling. If a mehndi stains black quickly, it almost certainly contains a chemical dye. Avoid black henna for tattoos, and avoid black hair “mehndi” unless the ingredients are clear and you have patch tested.

How do I patch test hair dye?

DermNet describes the self test recommended for consumers:

1. Mix a small amount of dye with the developer, as directed on the pack.
2. Apply a small spot behind the ear or on the inner elbow.
3. Let it dry and leave it uncovered for 48 to 72 hours.
4. If there is no itching, redness or rash, the risk of a reaction is lower.
5. If you react, do not use the dye.

The NHS also suggests a strand test on a lock of hair at least 48 hours before dyeing, and testing even if you use your regular brand.

Important limitations, according to DermNet:

• A negative self test does not guarantee you will not react.
• Repeated self testing can itself sensitise some people.

How can I dye my hair more safely?

The NHS and DermNet suggest:

• Wear gloves when applying dye.
• Apply petroleum jelly or a barrier cream along the hairline, ears and neck.
• Never leave dye on longer than the recommended time.
• Rinse thoroughly with mild shampoo afterwards.
• If you feel a reaction starting, wash the hair and scalp immediately with mild shampoo.
• If you have reacted to a permanent dye before, choose a non-permanent option, after testing.
• Tell your salon about any previous reaction.

What should I do if I have a reaction?

1. Stop using the dye and wash your hair and scalp thoroughly.
2. For mild symptoms, a pharmacist may suggest a moisturiser and an antihistamine, as the NHS advises.
3. For more severe or persistent symptoms, see a doctor. A doctor may prescribe treatment such as a steroid cream or tablets for a short time.
4. Do not self treat with strong steroid creams bought over the counter for long periods. See our article on topical steroid misuse.
5. Ask about patch testing. A dermatologist can confirm PPD allergy with formal patch tests and advise on alternatives.

Are there alternatives if I am allergic to PPD?

DermNet notes that:

• Semi-permanent dyes may be an option, but about 10 percent of people allergic to PPD also react to them.
• Dyes based on para-toluenediamine sulfate (PTDS) are tolerated by about half of people with PPD allergy.
• Metallic dyes and vegetable rinses can be used but do not give permanent colour.
• Patch testing is recommended before trying any alternative.

Some “herbal” or “natural” dyes still contain PPD or related chemicals, so always check labels.

How is hair dye allergy different from irritation?

Not every reaction is an allergy. Strong dyes, bleaches and developers can cause irritant contact dermatitis, a burning, sore reaction from direct chemical damage. Allergic reactions, in contrast, tend to be very itchy and can spread beyond where the dye touched. Both are forms of contact dermatitis, which the NHS describes as a rash caused by something the skin touches. A dermatologist can help tell them apart.

If you use dye to cover early grey hair, our article on premature grey hair discusses causes and options. For other forms of scalp itch, see dandruff and seborrheic dermatitis, and for itchy rashes elsewhere, see eczema in adults and children.

What about hairdressers and salon workers?

DermNet notes that hairdressers, who apply dye many times a day, are among those most at risk of PPD allergy and may develop hand dermatitis. Wearing suitable gloves for every colouring job, and avoiding direct skin contact with dye, helps protect against becoming sensitised. If you work in a salon and develop itchy, cracked hands, see a dermatologist, as patch testing can identify the cause.

When to see a dermatologist

See a dermatologist if:

• You have had a reaction to hair dye, mehndi or a temporary tattoo.
• Your scalp, face or eyelids are swollen, blistered or oozing.
• An itchy rash on your eyelids, ears or neck keeps returning after colouring.
• You want to find a safer way to keep colouring your hair.
• You have dark or light patches left behind after a reaction.

Swelling of the lips, tongue or throat, or difficulty breathing, needs emergency care. For non-urgent reactions or advice on safe colouring, Dr. Maria offers online consultations.