Dyeing your hair at home safely: the 48-hour allergy test and PPD

You can colour your hair at home, but every time you need a skin allergy test at least 48 hours ahead, a strand test on a small piece of hair, gloves, an open window, a timer set to the label, and a firm rule never to use hair dye on brows or lashes. This article explains why each of those matters, and which reactions mean going to hospital straight away.

Why the care: PPD

Many permanent hair dyes and some semi-permanent ones contain paraphenylenediamine, or PPD, which the FDA names as the hair dye ingredient most often linked to allergic reactions. A reaction can happen to someone who has dyed many times without trouble, because sensitivity can develop after repeated contact, and PPD exposure can also come from elsewhere, such as some textile dyes or “black henna” temporary tattoos.

According to the UK’s NHS, reactions usually look like stinging, burning, an itchy rash, dryness or tightness, soreness or blisters. Thailand’s Department of Medical Sciences lists signs such as swollen eyelids, face and lips, a red rash, an itchy scalp and, in severe cases, difficulty breathing. Symptoms can take up to 72 hours to appear. On brown or black skin, redness may look dark brown, purple or grey and be harder to see.

Two tests, two different questions

	Skin allergy test (patch test)	Strand test
What it answers	Does my skin react to this product?	What colour will I really get, and can my hair take it?
Where	As the package directs	A small hidden section of hair
When	At least 48 hours ahead, every time	Before the real dye job; can be done at the same time
Bad result	Stop. Do not dye	Change shade or timing as the label allows

Always follow the directions in that product’s box, because brands differ in amount, test site and mixing. If you feel unwell during the wait, the NHS says not to go on using that dye.

Test before every dye job, even with the same colour and brand. An allergy can start even after past uses went fine.

Example: planning your dye day

Say you want to dye on Saturday morning and the label says to leave the colour on for 30 minutes (an assumed number; use your label).

1. Wednesday 09:00: do the patch test as the label directs, and a strand test at the same time.
2. Friday 09:00: 48 hours have passed (2 days x 24 hours). Check the test site: no redness, itching, burning, swelling or bumps.
3. Saturday 09:00: 72 hours have passed, which also covers late-appearing reactions. If all is still normal, start.
4. 09:15: application done; start a 30-minute timer.
5. 09:45: rinse until the water runs clear, and rinse the scalp well.

Starting on Wednesday gives you the full 48-hour minimum plus the window of up to 72 hours in which reactions can still appear. Testing on Friday night and dyeing on Saturday morning would leave less than 12 hours to see a result, which is not enough.

While you dye

• Wear gloves for mixing, applying and rinsing, and wash your hands again after taking them off.
• Open windows and doors for fresh air. Some ingredients in hair colour give off vapours that can irritate the nose, throat and eyes. Keep containers closed when not in use.
• Do not leave it on longer than the label says. Use a timer. Longer does not give better colour; it only means more exposure.
• Do not dye if your scalp has cuts, scrapes or a skin condition, and do not scratch your scalp hard beforehand.
• Keep it out of your eyes. Hair dye ingredients can irritate or injure the eyes.
• Rinse your scalp well when the time is up.
• Keep the kit and the dye away from children.

AAD dermatologists add: choose a shade within three shades of your natural colour, because going lighter than that needs stronger peroxide and damages hair more.

Never use hair dye on brows or lashes

There is no exception here. The FDA says dyeing eyebrows and eyelashes is not a permitted use for these hair dyes, and the label caution the FDA requires says doing so may cause blindness. Thailand’s Department of Medical Sciences also says never to use hair dye on lashes or brows. Hair dye is made for the hair on your head, not for skin or anywhere near the eyes.

Never use hair dye on eyebrows or eyelashes. It risks eye injury, up to blindness.

Black henna is not henna

Natural henna stains brown or orange-red. What is sold as “black henna” for temporary tattoos is often henna mixed with a PPD hair dye, or hair dye alone painted on skin. The FDA says PPD is not permitted in cosmetics applied to the skin and has received reports of skin injuries from these products. The NHS notes that having had a black henna tattoo can raise your risk of reacting to hair dye and other PPD products later.

If you react

• Mild, just starting: wash your hair and scalp with water and a mild shampoo straight away, and ask a pharmacist.
• Getting worse or not improving: see a doctor, and take the box or label with you.
• Emergency, call your local emergency number (1669 in Thailand) now if your lips, mouth, tongue or throat suddenly swell, you struggle to breathe or swallow, your skin or lips turn pale, grey or blue, or someone becomes confused, dizzy or faints. Do not drive yourself to hospital.

Common mistakes

What people do	Why it is risky
Skip the patch test because they used it before	An allergy can start at any time
Test, then wait only a few hours	Reactions can take up to 72 hours
Dye with bare hands	Full skin contact with the chemicals
Dye in a closed, windowless bathroom	More of the vapour is breathed in
Leave it on longer than the label	Longer exposure, more damage
Use hair dye on eyebrows	Risk of serious eye injury

If you also wear gel nails, the idea of allergy from repeated contact is similar: see Gel nail allergy: warning signs and how to lower the risk. This article is general information, not diagnosis or treatment. If you have a history of allergies, talk to a dermatologist before colouring your hair.

Sources

• Hair Dyes — U.S. Food and Drug Administration
• Temporary Tattoos, Henna/Mehndi, and “Black Henna”: Fact Sheet — U.S. Food and Drug Administration
• Hair dye reactions — NHS
• Department of Medical Sciences advice on hair dye allergy (Thai) — Manager Online
• Hair Color, Licensee Fact Sheet 9 — California Board of Barbering and Cosmetology
• Coloring and perming tips — American Academy of Dermatology