My daughter 2 years constantly itches her head but no dendruff or eczema, changed several shampoos. what can it be?

Head lice? ringworm?: Itchy scalp can mean many things, including treatable causes, such as head lice (pediculosis capitis) or ringworm (tinea capitis. I would start by bringing your daughter to see her doctor, who may find a treatable cause, or may recommend therapeutic shampoos for conditions such as seborrheic dermatitis, or creams for eczema.

Unsure: Usually, i see this kind of problem in much older people, and often can't find a cause. One simple thing to try is a 1% Hydrocortisone liquid that's rubbed in up to twice a day. One brand i know of is scalpicin maximum strength. I wouldn't try the regular scalpicin which contains salicylic acid - i'd be afraid it would make the itch worse. Any chance there could be head lice?