Henna also imparts a temporary resin, which can easily be removed with a clarifying baking soda rinse (which is followed by a diluted vinegar rinse of 2tsp vinegar to 2.5 cups of water and a deep moisturising treatment), or sulfate-based shampoo followed by a deep moisturising treatment.

Before You Purchase: The Beginner
Originally Posted by juanab
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.
3a/b, F, normal porosity

Wash with either Suave Tropical Coconut, As I Am, or CJ Daily Fix
Condition with STC or Yes to Blueberries and detangle with Denman, rinse very lightly (baptismal rinse)
Add LAL gel, either Sport or Wet Look, scrunch with flour sack towel, and plop
Diffuse 5 minutes, then air dry