Can a patient with a history of allergic contact dermatitis to hair dye, specifically sensitized to phenylenediamine (PPD), undergo a patch test, and what are the potential severe side effects?

From the Guidelines

I would not recommend performing a patch test with phenylenediamine (PPD) on a patient with a clear history of allergic contact dermatitis to hair dye. Patch testing in this case is unnecessary and potentially dangerous since the diagnosis is already established by the patient's history, as suggested by the guidelines for the management of contact dermatitis 1. The most dangerous side effects that could occur include severe allergic reactions such as widespread contact dermatitis, anaphylaxis, angioedema, and even systemic reactions that could be life-threatening.

Instead of patch testing, advise the patient to strictly avoid PPD-containing products, including permanent and semi-permanent hair dyes. Provide them with information about PPD-free alternatives like vegetable-based dyes, henna products without PPD additives, or highlighting techniques that don't contact the scalp. The patient should also be educated about cross-reactors with PPD, including certain textile dyes, local anesthetics, and some medications, as noted in the guidelines for the management of contact dermatitis 1.

This approach prioritizes patient safety while still addressing their hair coloring needs through safer alternatives. According to the diagnosis and management of anaphylaxis guidelines, there might be circumstances in which allergy skin tests, in vitro specific IgE tests, and/or challenge tests might not be warranted, especially when the clinical history of anaphylaxis to a specific agent is strong 1. In this case, the patient's clear history of allergic contact dermatitis to hair dye containing PPD makes patch testing unnecessary and potentially hazardous.

Some key points to consider when managing a patient with a history of allergic contact dermatitis to hair dye include:

• Avoiding PPD-containing products
• Providing information about PPD-free alternatives
• Educating the patient about cross-reactors with PPD
• Prioritizing patient safety while addressing their hair coloring needs through safer alternatives, as recommended by the British Association of Dermatologists' guidelines for the management of contact dermatitis 1.

From the FDA Drug Label

if you notice any skin trouble or other unexpected reaction such as rash, irritation discontinue use immediately and ask a doctor The FDA drug label does not answer the question.

From the Research

Patch Testing for Allergic Contact Dermatitis to Hair Dye

• Patch testing can be performed on patients with a clear history of allergic contact dermatitis to hair dye, but it is essential to exercise caution due to the potential for cross-reactions with other hair dye components 2.
• The study by 2 suggests that patients allergic to para-phenylenediamine (PPD) should be cautious when using hairdressing materials and recommends performing patch tests to identify safe agents.
• Another study by 3 found that hair dye allergy may cause severe clinical reactions, and the current regulation is insufficient in protecting users, highlighting the need for a preventive strategy.

Potential Side Effects of Patch Testing with Phenylenediamine

• The most dangerous side effects that can occur in patients with allergic contact dermatitis to hair dye include severe allergic reactions, such as anaphylaxis, and exacerbation of existing dermatitis 4.
• A study by 5 found that strong reactions to PPD increased the risk of cross-reactions with other related compounds, including benzocaine.
• The study by 6 also found that PPD identifies the majority of positive reactions to other hair dye ingredients, but not all, which justifies additional testing with hair dye ingredients from the used product.

Precautions and Recommendations

• Patients with a history of allergic contact dermatitis to hair dye should be advised to perform hairdressing series patch tests and use other hairdressing materials with care, such as bleaching agents, shampoos, and especially hair-dye components other than PPD, due to cross-reaction 2.
• A preventive strategy is needed to protect the public from allergy to chemicals in consumer products, and immunologic and epidemiologic data should be used by regulatory authorities 4.
• The study by 5 recommends assessing the frequency of positive patch test reactions to PPDA and related chemicals among patients with allergic contact dermatitis and analyzing them regarding their clinical pattern, occupation, and cross-reactions.