Benzylalcohol is a simple aromatic alcohol. It is used to preserve ophthalmic, injectable and oral drugs also, besides cosmetics. Benzylalcohol-DHA is most active against bacteria and yeast but is weak against mold. Therefore, it is combined with DHA (dehydroacetic acid) which is very strong against fungi with some activity against bacteria; DHA is also permitted in food. Benzyl alcohol/DHA has poor performance above pH 7 best pH is 5-6. It will be inactivated in products with a higher pH such as soaps or hair relaxing products. Please note that benzylalchol-DHA may not perform well in nonionic formulations. It can be inactivated by nonionic surfactants. So it's better to formulate a shampoo with anionic and amphoteric surfactants rather than nonionic surfactants. Or combine a nonionic emulsifier with anionic emulsifiers, eg. stearic acid.