Researchers looked at over 100 hair dyes and found that phenylenediamine (PPD), which can cause allergic contact dermatitis, was present in 89% of products. “There’s no real reason your body should identify PPD as a pathogen, but sometimes, it does. So it activates an immune response that results in a rash,” says Dathan Hamann, a researcher at the University of Arizona who presented the study. But it’s not just PPD that could be making you itch: researchers found that hair dyes have an average of six dye compounds that can cause a reaction. (And this is only considering color-creating compounds, not other potentially irritating ingredients.) “There are probably more,” says Hamann. So if you have a go-to hair dye and haven’t had a problem, stick with it. But if you’ve had a reaction in the past and you’re looking to try something new, Hamann suggests a patch test. “It’s not just putting a spot of dye on your skin per the product’s instructions,” he explains. “It’s when your dermatologist applies different compounds to the skin to identify the root of the problem.” Note: Contact dermatitis is a specialized field, so this may be a time to cheat on your derm. Hamann suggests finding an expert via contactderm.org. Once you establish the culprit, you can find the best hair dye for you. More from Prevention: The Best At-Home Hair Color Tips
