Para-phenylenediamine (PPD) is a chemical ingredient used in hair dyes to give them the desired color. It is a highly allergenic substance, so it is important to perform a skin test before using it.

PPD is an aromatic molecule obtained by distillation of benzene. It is a solid substance, white in color, with a pungent odor. It is soluble in water, alcohol, and acetone.

PPD acts on the hair by breaking the sulfur bonds that link keratin molecules, the protein that constitutes the main structure of the hair. In this way, the coloring pigments can penetrate inside the hair and give it the desired color.

PPD is a very effective ingredient for hair coloring, but it is also a potentially dangerous substance. Indeed, it can cause skin allergies, which are manifested by redness, swelling, itching, and, in severe cases, blisters.

To reduce the risk of allergies, it is important to perform a skin test before using PPD. The test involves applying a small amount of the product on the skin of the arm and waiting 24 hours. If no allergic reaction occurs, the product can be used safely.

Furthermore, it is important to use PPD correctly, following the instructions on the packaging. The product should be applied to clean, dry hair, and should be left on for the indicated time.