According to Salon.com:
There are two types of ingredients in shampoo. One type cleans your hair. The other type strokes your emotions.
Shampoo has one main ingredient:
The two most common shampoo detergents are ammonium lauryl sulphate and ammonium laureth sulphate. That’s all you need to clean your hair. All those shampoo bottles. All that supermarket shelf space offer THE SAME PRODUCT.
Other ingredients include: perfume, dye, preservative, foaming agent, acid (The problem is hair swells in an alkaline solution eg with soap when rinsed out the hair shrinks making knots impossible to brush out. ARggghhhhh!), thickeners, thinners, sheen additive, pearlesence powder (makes shampoo look pearly) etc
According to Steve Antczak, Co-author of Cosmetics Unmasked: Your family guide to safe cosmetics and allergy-free toiletries,
A typical shampoo is mostly water, containing between 5 and 20 per cent detergent, with shampoo for dry hair containing less detergent than shampoo for greasy hair.
See New Scientist, Sept , 2009
So the potency of shampoo looks something like this:
Assume you buy a 500ml bottle of shampoo for $10. Now you can work out how much some shampoo manufacturers rip you off by filling in this table:
How much do you pay for water in shampoo? The Answer is here. Mathspig % detergent in shampoo ANS.
What does Bill Bunn from Salon.com recommend?
My new shampoo, Sunlight Dish Detergent, has just four ingredients. It’s runny and slightly acidic, smells vaguely lemony, doesn’t foam excessively and looks anemic.