About one pump is about right for medium length hair. Professional shampoo is very concentrated so only a small amount is necessary.
Generally speaking:
-
Wet your hair thoroughly
Apply the shampoo to your hair
Lather
Rinse thoroughly
But, as always, read the instructions on your particular shampoo to ensure that you are using it correctly!
If you are looking for a change consider trying TIGI's Eco Awesome from their Love Peace and the Planet range. It's organic.
