
Lets get the boring numbers paragraph out of the way. The general consensus is that you use a quarter-sized drop (apologies for non-Americans-think 20p). The average shampoo bottle looks to be 300ml, and it lasts around 1.5 months (un-scientific). Therefore, you're using roughly 6.7ml per wash. If that bottle costs $5, that's 11 cents per wash. From being a cheapo, and tipping my bottle over, I know I can get 5 more days out of the bottle, which means there's on average 33.3ml that is very stubborn in your shampoo bottle, or 55 cents worth. Many shampoo manufacturers (think Unilever, Procter & Gamble) still shy away from those bottles that sit upside-down, and I'm guessing this is for economic reasons. If the average consumer has a 50 year window of purchasing their own shampoo, they would buy roughly 400 bottles of shampoo ($2K worth). However, if that bottle was upside down, they'd buy 365 bottles ($1825), a savings of $175, or 175 items from your local fast food joint's dollar menu. Solution: these companies could charge $5.48 on average for the upside-down bottles, and all would be happy with less waste in the world. Oddly enough, those upside-down bottles do appear to be more expensive.
As an interesting aside, in researching the finer points of this post, I read in NPR that Americans apparently love shampoo--washing our hair an average of 4.59 times per week (twice as much as Italians and Spaniards). The article goes deeper by showing the tides supposedly all changed in May or 1908 when the NYT advised women they could deviate from the standard once per month wash, and do it every 2 weeks. Later, TV commercials featured models like Farrah Fawcett, and washing your hair was cool. According to dermatologists, 2-3 times per week should do the trick, as much more than this will remove too much sebum oil, which makes the sebaceous glands produce even more of that stuff, whatever it does. This ads an interesting twist in the life cycle of the shampoo bottle,. I may find myself needing to flip it upside-down less often, buy less, and only deal with the consequence of more flies loving my head on the way to work. I guess less really is more.