1. PPD
PPD is short for para-phenylenediamine. It is used as a dye for dark color shades and is made from coal tar, a petroleum-derived chemical that includes benzene,naphthalene, phenols, aniline, and other chemicals. It is also used as a wood preservative, and contact with skin is best to be avoided. Research states PPD in combination with Hydrogene Peroxide is very toxic and can lead to cancer.