What's Actually in Permanent Hair Dye

A routine product with a surprisingly harsh ingredient list.

Coloring your hair is normal and, for most people, fine. It's still worth knowing what the process involves.

The reactive chemistry

Permanent dyes work by opening the hair cuticle with ammonia (or a gentler substitute) and developing color with peroxide, using dye precursors like PPD (paraphenylenediamine). PPD is a fairly common cause of allergic reactions — which is exactly why the box tells you to do a patch test.

Putting it in perspective

Studies on personal hair-dye use and serious health risks have been largely reassuring for typical use, though exposure is higher for salon workers who handle it all day. Darker, permanent dyes tend to use more of the reactive ingredients than temporary or lighter ones.

The move

Do the patch test — really — especially the first time or with a new brand, and color in a ventilated space. If you react to PPD, look for PPD-free or gentler semi-permanent dyes. And for the pros doing it daily, gloves and ventilation matter most.

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