Does hair dye affect the health of the human scalp?

Sometimes: Hair dyes can lead to both skin irritation (contact dermatitis) & allergic reactions. This is largely because some dyes contain parphenylendiamine. The skin that was in contact with the dye may become dry, red, swollen, blistered, cracked or pustules are sometimes seen. An allergic reaction may lead to generalized itching, facial/ scalp swelling or in some severe cases to anaphylaxis.