What is PPD in hair dye?

What PPD is

We work from documents and have not tested any products. This page collects what a few public sources say about one hair dye ingredient, and it marks where they stop. It is not medical advice.

DermNet, a dermatology reference (retrieved 2026-11-14), says paraphenylenediamine (PPD) is “a chemical substance that is widely used as a permanent hair dye.” It gives the reason as a permanent dye that “gives a natural look”, and adds that the dyed hair can be shampooed or permed without losing its colour.

DermNet also describes how it works. The base PPD is colourless and needs oxygen to become a dye, so PPD hair dyes are usually packaged as two bottles, one with the dye and one with a developer or oxidiser. It says darker shades contain higher concentrations of PPD than lighter ones, and that darker shades are often used by people with naturally dark hair.

What it is called on an ingredient list

The EU’s glossary of common ingredient names, Commission Decision (EU) 2019/701 (retrieved 2026-11-14), contains these entries, found by searching the glossary text:

• P-PHENYLENEDIAMINE, entry number 20428
• P-PHENYLENEDIAMINE SULFATE, entry number 20430
• P-PHENYLENEDIAMINE HCL, entry number 20429
• TOLUENE-2,5-DIAMINE, entry number 25116
• TOLUENE-2,5-DIAMINE SULFATE, entry number 25117

Those are the EU glossary names. The sources we read say nothing about wording on US labels, so we do not state a US name.

Why it matters on an allergy site

DermNet says: “Fully oxidized PPD is not a sensitiser, but the intermediate, partially oxidised form of PPD may cause contact allergic dermatitis in sensitive individuals.” It says PPD was declared the Contact Allergen of the Year for 2006 by the American Contact Dermatitis Society.

On how the reaction presents, DermNet says PPD allergy “usually presents as acute, subacute, or chronic allergic contact dermatitis on areas in direct contact with the dye.” It says the exposure that starts the reaction may cause no symptoms. Later contact tends to produce a reaction more quickly, from a few hours to a few days, that becomes increasingly severe and extensive and lasts longer. A mild reaction to hair dye usually shows as an itchy dry rash on the upper eyelids or the rims of the ears.

DermNet names groups it says are affected: hairdressers, who often apply dye to clients several times a day, and hairdressing clients, especially those using darker shades. It says allergy is more common in people with skin of colour than in light-skinned people, and that the prevalence of hair dye reactions has increased as dyeing hair has become popular among males and females of all ages. People who work with PPD, such as hairdressers and photographers developing film, may develop hand dermatitis.

The same page says high concentrations of PPD in black temporary tattoos “may result in intense blistering reactions” at the site within 1 to 2 days. One 2010 abstract (PMID 20113350, Experimental Dermatology) says patients sensitised to PPD by semi-permanent tattoos “increasingly develop threatening allergic reactions in response to black hair dye.”

Toluene-2,5-diamine, a related ingredient

A 2025 abstract in Cutis (PMID 41524634) says toluene-2,5-diamine sulfate was named the American Contact Dermatitis Society’s 2025 Allergen of the Year. It says the substance “is widely used as an alternative to para-phenylenediamine (PPD) in hair dyes but is itself a potent and likely underreported contact allergen,” and that cross-reactivity with PPD is common. It says reactions look similar to PPD reactions and disproportionately affect hairdressers and frequent hair dye users. Its clinical recommendations include patch testing for both substances, with consideration of delayed readings.

This is why a “PPD-free” front label is not a complete answer in these sources: an ingredient that replaces PPD may be a related allergen. We found no source that says which products use which ingredient, so we make no product claims.

What individual studies report

These are single studies, reported as they describe themselves, not general conclusions.

• A 2017 study in Contact Dermatitis (PMID 27555055) extracted 8,036 patients patch tested with the European baseline series. Of these, 251 were sensitised to PPD and/or toluene-2,5-diamine, with 231 sensitised to PPD and 109 to toluene-2,5-diamine. It reports that cross-reactivity was commonly found among people sensitised to either and was strongly related to the strength of the patch test reaction.
• A 2026 abstract in Dermatitis (PMID 41649178) reviewed 666 patients patch tested between 2005 and 2023 at a clinic in Athens. PPD was the most frequent allergen at 47.9%, followed by toluene-2,5-diamine at 35.9% among the dye allergens, with nickel (41.1%) ranking between them in the abstract’s list. It reports significant co-sensitisation with chemically related compounds including 4-aminophenol, 3-aminophenol, benzocaine, textile dyes, hydroquinone and pyrogallol, and says 7% of patients sensitised to para-amino compounds would be missed by PPD testing alone. These patients were people referred for suspected hair dye allergy, so the percentages describe a clinic population, not the general public.
• The 2010 abstract above (PMID 20113350) examined nine patients with severe reactions to permanent hair dye. It reports that standard patch tests with 1% or 0.5% PPD produced severe and sometimes blistering reactions in all PPD-responsive patients, and it describes iatrogenic (test-caused) sensitisations as having been described. The authors evaluated a blood-based lymphocyte test as a possible alternative to patch testing in severe cases. That is a laboratory method from one small study.

Together, these sources describe PPD and toluene-2,5-diamine as the main sensitisers in the hair dye allergy they studied, with overlap between them. They do not tell us how often any particular product causes a reaction.

What the FDA says about hair dye labels

The FDA’s Hair Dyes page (retrieved 2026-11-14) says most hair dyes belong to a category called “coal-tar” hair dyes, which include permanent, semi-permanent and temporary dyes, and that these do not need FDA approval, unlike color additives in general. It says FDA’s ability to take action against coal-tar hair dyes associated with safety concerns “is limited by law,” so it is important for consumers to follow the directions on the label.

It says the FDA cannot take action against a coal-tar hair dye on the basis that it is or contains a harmful ingredient as long as the label includes a special cautionary statement and the product comes with adequate directions for a skin test before dyeing. The statement reads:

Caution - This product contains ingredients which may cause skin irritation on certain individuals and a preliminary test according to accompanying directions should first be made. This product must not be used for dyeing the eyelashes or eyebrows; to do so may cause blindness.

DermNet makes a similar point: it says preparations containing PPD or its derivatives carry a warning on the packaging recommending a self patch test. DermNet also says a negative result does not guarantee freedom from reaction, because the patch test itself could cause sensitisation. We read the FDA wording as describing a labelling condition, and we do not read it as medical guidance. For your own skin, ask a dermatologist.

How this site treats it

This is our own approach, not a regulation or medical judgement. Where a page on this site discusses a hair dye or a maker’s “hypoallergenic” claim, we read the maker’s published ingredient list and compare it with the names above. A “hypoallergenic” or “PPD-free” label is a maker’s wording; see what hypoallergenic means and our guide to hypoallergenic hair dye labels, and PPD vs PTD. Related reading: hypoallergenic shampoo, hypoallergenic eyelash glue, hypoallergenic mascara, hypoallergenic makeup, hypoallergenic lotion and hypoallergenic products on a budget. For metal allergy rather than dye allergy, see nickel allergy and jewelry.

A plain line

These sources describe an ingredient that some people react to, and they do not say everyone will. If you have had a rash from hair dye, a reaction to a black temporary tattoo, or work with dye, ask a dermatologist. Patch testing and diagnosis are clinical matters.

What we don’t fully know

We found no source on PPD concentrations in specific products, on legal limits, or on whether “PPD-free” dyes are less likely to cause reactions. We read abstracts rather than full papers, and different clinics report different rates. The rest is listed under “unknowns” on this page.