Although clean hair is desirable and even necessary for the maintenance of healthy hair, excessive shampooing can strip vital minerals like calcium, phosphorus, nitrogen and iron from the hair. This is particularly true when using commercial shampoos. Most commercial shampoos contain formaldehyde as a preservative. To disguise the presence of formaldehyde it is listed in the ingredients as Quanternium-15. This substance can be carcinogenic (cancer-causing) and poisonous to the entire system.