Some of the most common ingredients in hair dye are coal tar, DMDM hydantoin, formaldehyde, and phenyl methyl pyrazolone.
Coal tar is found in some of the darker hair dyes and it is harmful because it can penetrate the skin and irritate the scalp. Testing with animals has also proved that it can cause cancer.
Formaldehyde can cause cancer and can also harm a growing fetus. A dye with this substance should never be used by a pregnant woman. DMDM hydantoin is very dangerous because it can cause immune system problems.
Phenyl methyl pyrazolone is an oxidizing agent. It is harmful to the hair because it can cause extreme dryness and irritation as well as headaches, coughs, and shortness of breath.
Toluene is an ingredient that is found in many of the lighter hair colors. This ingredient can also cause extreme dryness and irritation on the scalp. This is very dangerous for dry and curly hair textures because it can cause split ends and breakage.
Hair dyes should be used sparingly and with extra caution because there are many dangerous ingredients in them.