Shampoo for infant (rashes)

What shampoo to use if LO is prone to having rashes on the head, face and ears? Did an allergy test and he's not having eczema so I suspected it's the shampoo we used on him. Have used Kodomo, Johnson's Head to Toe (used on his body too and no rashes except the head) but when the rashes striked then switched to Aveeno and Suu Balm Kids but see no difference. Tried hard not to put the steroid cream on him but seeing him scratch & cry when he sleeps make me feel so bad 😭 He's almost 5 mths old. #advicepls #pleasehelp