This will not remove the henna itself--henna bonds to the keratin, which is why it's so difficult or impossible to remove. It just removes the resin coating. The lawsone (dye) is not removed.
Former longhair, now CG, living in N. California where the fog meets the wind
3a/b, fine, normal porosity/elasticity, high density
Conditioner wash and style, sometimes with a dab of BRHG.