Avoid harsh soaps and detergents: you'll especially want to avoid products that contains sodium lauryl sulfate as it can dry and irritate the scalp (beautyzion.com)
You should in particular ensure that the shampoo doesn't contain sodium lauryl sulfate which is a commonly used lathering (beautyzion.com)
Many concerns surround the widespread use of Sodium lauryl sulphate (SLS) and its relatives sodium laureth sulphate (SLeS), sodium coco sulphate and ammonium lauryl sulphate (ALS). (odylique.com)