A hair dye patch test, often called an allergy alert test, is the small test that the leaflet tells you to do before coloring your hair. It is tempting to skip, especially when you have used the same shade for years. It is worth the two days, because reactions to hair dye can be serious and can develop at any time.
Why the test matters
Many permanent and some semi-permanent hair dyes contain paraphenylenediamine (PPD) or related chemicals. These are effective dyes, and they are also well-known causes of allergic reactions. An allergy can appear:
- The first time you use a product.
- After years of using it without trouble.
- After a "black henna" temporary tattoo, which often contains high levels of PPD and can make a person allergic for life.
Always follow the leaflet in your box
Instructions differ between brands. The steps below describe the usual method, but the leaflet that comes with your product is the one to follow, including where to apply the test, how to mix it and how long to wait.
The usual method
- Do the test 48 hours before coloring, every time.
- Choose the test spot named in the leaflet, usually behind the ear or in the bend of the elbow.
- Clean and dry the area.
- Apply a small amount of the product as directed. Some brands ask you to use the colorant alone, others a mix of colorant and developer.
- Leave it to dry and do not wash, cover or touch it for 48 hours, or the time stated.
- Check the area during and at the end of the period.
Reading the result
| What you see | What to do |
|---|---|
| No change | Proceed with coloring as directed |
| Redness, itching, swelling, soreness or a rash at the spot | Wash it off. Do not use the product |
| Reaction beyond the test spot, swelling of the face or eyes, hives, feeling unwell | Seek medical help promptly |
| Difficulty breathing, swelling of the mouth or throat | Call emergency services immediately |
If you react, do not try a different brand without medical advice. Many dyes share the same chemicals.
A patch test is not a strand test
The leaflet may mention both.
- The allergy test checks how your skin reacts.
- The strand test applies dye to a small, hidden lock of hair to check the color result and timing.
Do both when the instructions ask for them.
Limits of the test
A clear test lowers the risk but does not remove it. Stop and rinse immediately if you feel burning, stinging or itching during coloring. Mild irritation from the product is different from allergy, but neither should be ignored.
What a reaction to hair dye looks like
- Mild irritation: stinging, redness or dryness on the scalp, neck, forehead, ears or eyelids, usually within 48 hours.
- Allergic reaction: itching, swelling of the scalp and face, puffy eyelids and a red rash that may spread. Symptoms can take hours or a day or two to appear.
- Severe reaction (anaphylaxis): swelling of the lips, mouth or throat, wheezing, faintness. This is an emergency.
After any reaction, wash your hair and scalp thoroughly with a mild shampoo, and see a doctor. A dermatologist can arrange patch testing to identify what you are allergic to.
Safer coloring habits
- Wear the gloves provided.
- Keep dye off your skin, and rinse the scalp well afterwards.
- Do not leave dye on for longer than directed.
- Never use hair dye on eyebrows or eyelashes. It can injure the eyes.
- Do not color when your scalp is sore, scratched or sunburnt. See Sensitive Scalp Care: Tips for a Gentle Routine.
- Tell your hairdresser about any earlier reaction, and ask for a patch test at the salon before a new color.
If you are allergic to hair dye
Ask a dermatologist about your options. Some people can use dyes with different ingredients after testing. Others choose highlights that keep dye away from the scalp, pure plant-based colors, or their natural shade.
For general care after coloring, see Color-Treated Hair: A Simple Care Routine. For itching after a hair product, see Itchy Scalp: Common Causes and Care Options. The same test-first approach applies to skincare, as explained in How to Add New Products to Your Skincare Routine. To choose a shade, see How to Choose a Hair Color for Your Skin Tone.
Related on ArniSun
- Color-Treated Hair: A Simple Care Routine
- Sensitive Scalp Care: Tips for a Gentle Routine
- Itchy Scalp: Common Causes and Care Options
- How to Add New Products to Your Skincare Routine
- How to Choose a Hair Color for Your Skin Tone
Sources and further reading
Frequently asked questions
Do I need to patch test every time I dye my hair?
Yes. An allergy can develop at any time, even to a product you have used for years, and formulas can change.
Can I do the patch test 24 hours before instead of 48?
Follow the time in your leaflet, which is usually 48 hours. Allergic reactions are often delayed, and a shorter test can miss them.
Are "PPD-free" or natural dyes safe for people with a dye allergy?
Not automatically. Many contain related chemicals that can cause the same reaction. Get advice from a dermatologist before trying one.