From the Guidelines
Yes, you can perform a patch test on a patient with a clear history of allergic contact dermatitis to hair dye, but with important precautions to minimize the risk of adverse reactions. The patch test should be performed in a controlled clinical setting with close monitoring, and the patient should be fully informed about the small risk of exacerbating their dermatitis, as advised by the British Association of Dermatologists' guidelines for the management of contact dermatitis 2017 1. When conducting the patch test, it is essential to use significantly reduced concentrations of para-phenylenediamine (PPD), typically 0.5% or lower in petrolatum, rather than the standard 1% concentration, to minimize the risk of strong reactions. The patient should be counselled on the need to avoid exercise, keep the back dry, and be aware of possible adverse effects, including skin reddening, itching, and occasional blistering at the application site, as outlined in the guidelines 1. Prepared patch test series, such as the TRUE® or Epiquick® tests, can be used, as they are more reliable than operator-prepared tests, according to the British Association of Dermatologists' guidelines 1. Key considerations for the patch test include:
- Using reduced concentrations of PPD to minimize the risk of adverse reactions
- Conducting the test in a controlled clinical setting with close monitoring
- Fully informing the patient about the potential risks and benefits of the patch test
- Counselling the patient on how to minimize the risk of adverse effects during the test. By taking these precautions and following the guidelines, the patch test can be a valuable tool in confirming the specific allergen and identifying potential cross-reactors, ultimately helping patients avoid future exposures to harmful substances.
From the Research
Patch Testing for Allergic Contact Dermatitis to Hair Dye
- Patch testing is a common method used to diagnose allergic contact dermatitis, including reactions to hair dye [(2,3,4,5,6)].
- However, for patients with a clear history of allergic contact dermatitis to hair dye, patch testing may pose a risk of triggering an allergic reaction, particularly to the substance phenylenediamine (PPD) present in the dye [(3,4,6)].
Risks and Precautions
- Studies have shown that PPD is a common allergen in hair dye, and patients with a history of allergic contact dermatitis to hair dye may be at risk of reacting to PPD [(2,3,4,5,6)].
- Patch testing with commercial hair dye products has been shown to elicit positive reactions in patients with allergic contact dermatitis to PPD, even with products labeled as "hypoallergenic" or "non-allergenic" 3.
- Therefore, it is essential to exercise caution when performing patch testing on patients with a history of allergic contact dermatitis to hair dye, and to consider alternative testing methods or precautions to minimize the risk of an allergic reaction [(3,5)].
Alternative Testing Methods
- Some studies suggest that performing sensitivity testing prior to the actual use of any hair dye product, irrespective of how it is advertised or labeled, may be a safer approach [(3,6)].
- Additionally, using a hairdressing series patch test may help identify safe alternatives for patients with allergic contact dermatitis to PPD 5.