Article: If the amount of shampoo you use is bigger than a quarter, you're using too much. Unless your hair is very thick or very, very long, a quarter-sized amount is enough. If your hair is very thick or long, you can double the amount you use, but you shouldn't use a full handful of shampoo on your head no matter how long or thick your hair is.

What is a summary?
Use the right amount of shampoo.