Are All Soaps Created Equal?
ANDREA SEABROOK, Host:
Well, that's what you think.
(SOUNDBITE OF MUSIC)
SEABROOK: Professor McNeil, here's the question for you. Can I wash my hair with Palmolive?
STEPHEN MCNEIL: And so you know, probably for your shampoo, you want it to clean, and you want it to condition, and you want it to moisturize, and you want it to do some other things to make your hair look pretty.
SEABROOK: Okay, but hold on. Aside from all that stuff, listen, I was in my shower this morning, thinking about this very interview, and I was looking around at the products in my shower. And so I took a plastic shopping bag, and I brought in some things. I have some shampoo, I have some hand soap here. I've got a bar of soap for my body. And you're telling me that in this Palmolive I have here also, the same thing is in all of these products to cleanse - the basics of cleansing chemicals is the same.
MCNEIL: All cleaning agents are going to contain detergent molecules, species that act as what's called a surfactant, which helps to break down the surface tension of the water so that it will coat the surface or penetrate the fabric more effectively. And they also actually encapsulate and trap the dirt molecules or the oil particles and lift them up and carry them away. So probably your shampoo contains something like sodium lauryl sulfate.
SEABROOK: Yeah, I was just going to say that. I'm looking at these things.
MCNEIL: Almost all of them have that.
SEABROOK: All of them say sodium laureth sulfate. Yeah.
MCNEIL: Yes. So there's - so that's your detergent, that's the primary cleaning agent. And to just get rid of the oil, that's all you need. The thing about your hair though is that there's actually a thin coating of naturally occurring oil that protects your hair and keeps it shiny, and keeps it smooth. And your detergent doesn't distinguish between the oil-grease build up in your hair that you're trying to get rid of.
MCNEIL: ...and the natural oil so it strips that off.
MCNEIL: And if you just left it - in other words, if you just use soap to clean your hair - then your hair is going to be dry, and it's going to be brittle, and it's going to build up lots of static, and it's frizzy and flyaway and then you're a horrible human being.
(SOUNDBITE OF LAUGHTER)
MCNEIL: After that, you're getting into stuff that isn't so much about making your hair look pretty as it is about making the shampoo look pretty.
MCNEIL: So you've got foaming agents like Cocamide DEA. That makes...
SEABROOK: Oh, yeah. That's in everything.
MCNEIL: That makes - it just makes suds. It doesn't do anything to clean it at all.
SEABROOK: Professor McNeil, did you just say that suds don't actually clean anything? I mean, come on. I'm lathering up. I'm washing it off. It's very satisfying.
MCNEIL: That can be indicative of useful cleansing, but it's not actually necessary. And they do really add things to these products, specifically, to create suds without increasing the cleansing power at all.
SEABROOK: Huh. Okay. So okay. Let me turn to the laundry detergent. Isn't that - I mean, isn't that actually a little different than soap?
MCNEIL: It sure is. You're operating in a different environment. You're usually things at a different temperature. Types of stains that you're trying to remove from clothing - particular things like grass and blood stains, which, hopefully, you don't get in your hair very often.
(SOUNDBITE OF LAUGHTER)
MCNEIL: So you actually have enzymatic cleansers that will break down the protein stains like grass stains and blood stains. Another group of compounds you would often find added to detergents are the whiteners or the brighteners because, of course, your clothes have to be whiter than white and brighter than bright or, again, you're a worthless human being.
(SOUNDBITE OF LAUGHTER)
MCNEIL: And they'll actually add invisible dyes to detergents that fluoresce under UV light - that they glow.
SEABROOK: Oh, my gosh.
MCNEIL: And you get just enough of this effect in sunlight that clothing that's been treated with this dye will seem to glow a little bit and it seems brighter than it is. This doesn't clean your clothes at all, but it makes it look brighter and so it's a cheat to make you think that your clothes are cleaner than they're actually getting.
SEABROOK: Oh, my gosh. That's amazing.
MCNEIL: And that's in pretty much in any detergent that you buy.
SEABROOK: Well, Professor McNeil, thank you so much for clearing up the differences or the not differences between my products here.
MCNEIL: You're very welcome.
SEABROOK: Chemistry Professor Stephen McNeil joined us from the CBC's studio in Kelowna, British Columbia. Thank you so much, professor.
MCNEIL: You're welcome.
SEABROOK: And thanks to listener Kendra Zanzo(ph), who sent us the question about the different kinds of soap. [POST-BROADCAST CORRECTION: An earlier version of this report said the CBC's studio is in Colona, British Columbia. That was a misspelling of the city's name. It is Kelowna.]
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
Correction July 11, 2017
A previous version of this report said the CBC's studio is in Colona, British Columbia. That was a misspelling of the city's name. It is Kelowna.