Detergent vs Soap

Renae:

Hi, my name is Renae and I'm an appliance repair tech. If you've ever seen any of my videos before, you probably already know that if you have a high-efficiency washing machine, you only need to use two tablespoons of high-efficiency detergent with it. And whenever I post a video about that, I get a lot of comments from people saying the same thing. Usually, it's some version of, "If I don't see suds, my clothes aren't clean." Well, I hate to break it to you, but laundry detergent is actually designed to be low or no suds. And I think what's happening here is a lot of you guys are confusing detergent for soap. And I would love to explain the difference between the two, but I'm an appliance repair tech, not a chemistry teacher. Luckily though, I happen to know someone who is. So I'm going to let him do the talking.

Chemistry Teacher:

So what is the difference between a soap and a detergent? The definitions are not super well defined, but broadly speaking, soaps are derived from natural things like animal fat. Remember Fight Club? And detergents are synthetic or man-made. There's a lot of complexity and variety to both types, although because detergents are designed, there's way more variety there. But the important thing that makes them similar and makes them work is that both of them have a hydrophilic end, which is the side that loves water, and a hydrophobic tail, which is the side that hates water but does love things like oil, and dirt, and grease.

Chemistry Teacher:

Here's the thing about those soap molecules. When a bunch of them get together under the right conditions, they form a soap bubble. And they do this by turning their water-loving heads inward toward each other and their water-hating tails outward toward the air and on the inside of the bubble toward the inside of the bubble. But if you've got all those tails interacting with air, that means they're not interacting with the dirt and grease that you want to wash away. When they are touching the oils you want, then that means the other end is interacting with the water. Air is not getting trapped in, and you're not seeing that many bubbles.

Chemistry Teacher:

There's a wide variety of detergents out there, and some of them are designed to foam, but the ones designed to do their most efficient work in your high-efficiency washer are designed to do this, not make suds.