Despite its effectiveness in making the dye resistant to washing and drying, studies have linked its use to various health risks, ranging from skin allergies to poisoning and even the possibility of developing some types of cancer.
The body absorbs small amounts of PPD during cosmetic use, but these can lead to allergic reactions, with contact dermatitis and allergic rhinitis being the most common. Allergic reactions typically appear about 72 hours after skin contact and include redness, swelling, blistering, and intense itching. It is estimated that 1.5% of people may be allergic to PPD, and this percentage rises to 6% in those with pre-existing skin conditions such as eczema or rashes.
On the cancer front, the International Agency for Research on Cancer (IARC) classified hair dyes as "probably carcinogenic" when exposed to occupational substances, but considered that personal use does not classify them as causing cancer in humans.
A comprehensive 36-year study found no clear link between the use of permanent hair dyes and the risk of most types of cancer, although there is some evidence of a link between frequent use and specific subtypes of cancer, such as estrogen receptor-negative breast cancer and basal cell carcinoma, without the results being conclusive.
In cases of acute poisoning when PPD is taken orally, it can lead to rapid and severe failure of vital organs, usually manifesting as swelling of the neck and airways (angioedema), and may be fatal.
As awareness of the risks increased, PPD-free hair dye products emerged, using para-toluene diamine sulfate (PTDS) instead as a less allergenic alternative, noting that about half of those with PPD allergies may also react to PTDS.
To reduce risks, it is recommended to conduct a sensitivity test 48 hours before using any hair dye. Professionals handling these materials are advised to wear protective gloves, and consumers should be made more aware of the hazardous factors.