The most serius problems is: p-Phenylenediamine (PPD) is an organic compoun. This derivative of aniline is a white solid, but samples can darken due to air oxidation.  It is mainly used as a component of engineering polymers and composites like kevlar. It is also an ingredient in hair dyes and is occasionally used as a substitute for henna. Source: https://en.wikipedia.org/wiki/P-Phenylenediamine

According to the National Capital Poison Center, PPD is “one of the main culprits” of skin irritation caused from hair dye, and has been associated with both simple irritation:

  • Redness: From a sunburn to an allergic reaction, there are many things that can cause your skin to become red or irritated.
  • Itching: Itchy skin, also known as pruritus, is an irritating and uncontrollable sensation that makes you want to scratch to relieve the feeling.
  • Burning: are one of the most common household injuries, especially among children. The term “burn” means more than the burning sensation associated with this injury.

In some cases it can causes more serious allergic reactions.