What is a patch test?
A patch test, also known as a skin test, is when your stylist applies a small amount of hair colour either behind your ear or on your forearm. This is to check how your skin reacts to the colour brand your salon uses. The test stays on for about an hour, and then you wipe the area with a damp tissue. If you notice any reaction or irritation, you must let the salon know.
Does everyone have to have a patch test?
Yes! Whenever you’re having your hair coloured in a salon, it’s really important to have a skin test (patch test). This should be carried out at least 48 hours before your colour appointment. That way, there’s enough time to see if any allergic reactions develop.
But I’ve been colouring my hair for years…
This is something I hear often when booking appointments, but the truth is not all salons use the same colour brands. For example, you might have been fine with Wella, but your new salon might use L’Oréal — and the ingredients aren’t always the same. That’s why patch tests are essential for every new client.
My old salon uses the same brand as you.
Even if that’s the case, all salons must follow their insurance policies. Imagine a client hadn’t coloured their hair for over a year and, without realising, developed an allergy in that time. If we didn’t carry out a skin test, both the client and stylist could be at risk. So patch tests aren’t just about rules — they’re about protecting everyone’s safety.
How often do I need a skin test?
Skin tests should be carried out every 6 months.
- If you colour your hair only once or twice a year, you’ll need a new skin test every 6 months to make sure no allergies have developed.
- If you colour your hair regularly (say, every 6 weeks), then the patch test you had when you first joined your salon will usually cover you, as long as you keep up with your appointments.
I’m pregnant. Do I need a new skin test?
Yes, I would always recommend having a new skin test when you find out you’re pregnant, just to be on the safe side.
How bad can it be if I don’t have a patch test?
Not having a patch test can be very dangerous, and in some cases, it can even result in a hospital visit. Here are some possible reactions to hair dye:
Mild reactions:
- Burning
- Redness
- Itchiness
- Soreness
- Dryness on your neck, face, or scalp
Severe reactions:
- Breathing problems
- Wheezing
- Tight throat
- Swelling of lips, tongue, or face
- Blistering
What makes people allergic to hair dye?
The most common cause of allergic reactions to hair dye is a chemical called para-phenylenediamine (PPD).
What is PPD?
PPD (para-phenylenediamine) is a chemical used in permanent hair dye, particularly in darker shades.
Final thoughts
I know it can feel like a pain having to make that extra trip to the salon, but it’s so worth it for your health. Spending 20–30 minutes on a patch test not only keeps you safe, but it’s also a great chance to meet your stylist, have a consultation, and chat about your hair goals. That way, by the time your colour appointment arrives, you’ll both know what’s achievable — and you’ll have peace of mind knowing you’re not allergic to the dye.