Festive Hair Colour: How to Read the Ingredient List and Patch Test Properly

Hair colour is one of the few beauty products that can cause a serious allergic reaction. Festival season sends many people to the salon or the supermarket aisle for the first time in months, and often in a hurry. A few minutes with the box can save you a lot of trouble.

What's in permanent hair colour

Most permanent dyes work in two parts: a colour cream and a developer (peroxide). The colour cream usually contains an alkaline agent (often ammonia or a substitute) and dye precursors. The one allergy specialists mention most is PPD (para-phenylenediamine), sometimes listed as p-phenylenediamine, along with related ingredients such as toluene-2,5-diamine. Some people react to these quite strongly.

Read the label

• Look for PPD and related dyes in the ingredient list. If you've reacted to a dye before, avoid them.
• Check the dates. Manufacturing and expiry should be printed, along with a batch number.
• Check the instructions are on the pack in a language you can read, and that a patch test is described.
• "Herbal" or "ammonia-free" doesn't mean allergy-free. Many products with these claims still contain PPD or similar dyes.
• Be wary of "black henna". Pure henna is orange-brown. Products that stain skin black quickly often have PPD added.

How to patch test

1. Mix a small amount of colour and developer exactly as the pack says.
2. Apply it to a small area, such as behind the ear or the inner elbow. Let it dry.
3. Leave it for 48 hours without washing it off, and check for redness, itching, swelling or blistering.
4. If there's any reaction, wash it off and don't use the dye.

Repeat the test before every colouring session, even if you've used the same brand before. An allergy can develop at any time, and a clear test last year doesn't guarantee one this year.

While colouring

• Wear the gloves in the box and work in a ventilated room.
• Keep the dye away from your eyes. Don't use it on eyebrows or eyelashes.
• Apply to dry, unwashed hair if the instructions say so, and don't leave it on longer than stated.
• Don't mix products from different brands.

Stop and get medical help if

• Your scalp, face or eyelids swell.
• You develop severe itching, blistering or a rash.
• You have trouble breathing or swallowing. That's an emergency.

Hair care afterwards

Coloured hair is drier. Use a mild shampoo, a conditioner or mask once or twice a week, and heat protection if you style with heat. If you're seeing more shedding than usual, that's a separate thing: our October hair fall guide explains what's normal.

Quick answers

Can I colour my hair when pregnant?

Ask your doctor. Many people wait until after the first trimester, but advice varies.

Is salon colour safer than home colour?

The chemistry is often the same. A salon can do the patch test and application properly, but you still need to test.

How long should I wait between colouring sessions?

Usually four to six weeks for root touch-ups, but follow the product's instructions.

This is general information, not medical advice.