Contact Allergen of the Year: p-Phenylenediamine

Vincent A. DeLeo


Dermatitis. 2006;17(2):53-55. 

In This Article

Scope of the Problem

The primary route of exposure to PPD is through hair color, among consumers as well as among hairdressers. Allergy to the PPD in the consumer usually presents as a dermatitis of the face near the hair line and neck and may involve the eyelids, often sparing the scalp. In more severe cases, scalp dermatitis and more generalized eruptions may occur.[2] Immunoglobulin E (IgE)-mediated contact urticaria and anaphylaxis have been reported,[3,4] as have lymphomatoid reactions.[5] Theoretically, once oxidized, the PPD is no longer allergenic, but in reality, it is likely that the PPD is almost never completely oxidized.

Although the number of individuals that use hair dyes seems to be increasing, the incidence of positive patch-test reactions to this antigen among consumers at this point seems to have remained constant or to have even decreased slightly over the past decade ( Table 1[6,7,8,9,10]). In the biannual reports from the North American Contact Dermatitis Group, the incidence of positive patch-test results in their population of tested individuals has actually decreased from almost 7% to just less than 5% between 1994 to 1986 and 2001 to 2002.[6,7,8,9] A similar rate of incidence of approximately 5% was also reported by the Mayo Clinic group in their 1998-2000 test population.[10]

In contrast, reactions caused by occupational exposure appear to be increasing. Comparing the periods of 1980 to 1993 and 1994 to 2003, a study of more than 600 hairdressers found that the incidence of reactions to PPD increased from 45.9% to 58.0%.[11]

In addition to reactions related to hair coloring, PPD and related substances may be used to dye textiles and fur and can therefore be a cause of textile or clothing dye dermatitis. Testing with PPD alone, however, will not identify most individuals who are allergic to textile dyes.[12]

A number of chemically related compounds have been associated with cross-reactivity to PPD ( Table 2 ). These include a number of commonly used medications, including a relatively new cyclooxygenase-2 (COX-2) inhibitor (celecoxib), sunscreen agents, and antioxidants used in the manufacture of rubber products, such as N-isopropyl-N′-phenyl-p-phenylenediamine–agents in the black rubber mix patch-test allergen. The latter are more likely to cause problems in the workplace but may also be used in garments. These agents color the rubber black or grey.


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