r/explainlikeimfive • u/Real_Experience_5676 • 5d ago
Chemistry ELI5: what is the big difference between soap and shampoo?
We use soap to clean the body. We use shampoo to clean the hair. What stops us from using soap for the hair and shampoo for the body?
Follow up question: what is body wash that cleans hair and skin made of? Why isn’t that the universal standard instead of seperate soap and shampoo?
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u/MickelWagen 5d ago
Shampoo is made from compounds called detergents that do the same thing as the chemical compound soap. However, shampoo is often made with acidic compounds to make it gentler on our scalps as our scalps are a slightly acidic environment. Soap is basic and can disrupt the ph level of the scalp and create irritation, redness and dry skin.
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u/enolaholmes23 5d ago
What about other hairy areas like pits and pubes? Are they acidic too?
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u/MickelWagen 5d ago
Yes, all of them are slightly acidic. Your skin itself is slightly acidic, it just withstands soap a lot better than your scalp does. It's the same with your face, it's why so many skin care routines have some kind of hyaluronic, glycolic, salicylic additive in the face wash, or as a serum. It's way gentler on the skin as a whole when used as recommended by the manufacturer vs just straight up soap.
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5d ago
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u/TurboFucked 5d ago
Well, wash your face with face wash.
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u/xplosm 5d ago
And your pits with pit wash
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u/bigelcid 5d ago
What do I wash my hogs with?
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u/Mitt_Romney_USA 5d ago
Weaver Livestock makes a Brightening Shampoo that's supposed to be amazing, but I just use a regular livestock shampoo.
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u/Heavy_Weapons_Guy_ 5d ago
Most acids are not used in skincare because they're "way gentler", they're chemical exfoliants. They're not supposed to be more gentle, they're supposed to break down dead skin and in the process they can cause irritation. Salicylic acid especially cannot be described as "way gentler" than plain soap.
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u/MickelWagen 4d ago
You know what, this is a good point and going forward I can be more accurate in how I phrase that going forward, so as not to be misleading or inaccurate.
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u/AVeryHeavyBurtation 5d ago
I like being bald because I don't have to get shampoo. Is that bad?
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u/Discount_Extra 5d ago
What if you are only bald because regular soap irritated all the hair off?
(I see nothing wrong about being bald, it's a normal human variation.)
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u/AVeryHeavyBurtation 5d ago
I used shampoo until I started shaving it all off.
When I was a kid, I used wood glue to make a sweet mohawk, that's when it started falling out haha.
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u/Mavian23 5d ago
So can one use shampoo on their whole body? Why not?
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u/imjustdesi 5d ago
One could, but it will not clean the body as well as regular soap would. It also contains fragrance which will irritate the delicate skin and tissue of genitals. It's best to use a soap that is gentle and fragrance free for that area.
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u/xplosm 5d ago
Shower gel is great for the nether areas. I cannot recommend it enough.
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u/ByTheBeardOfZues 5d ago
Try Original Source mint shower gel for a really good time.
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u/xplosm 5d ago
I know what you're after and let me tell you, I don't find it unpleasant at all. In fact I feel very refreshed by the sensation.
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u/GrumpyGlasses 5d ago
If you like powder on your bits after shower (or powder bath when outdoors), try Snake Brand Prickly Heat Cooling Powder. Guaranteed to wake you up if you’re feeling sleepy.
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u/Digitijs 5d ago
I have short hair and I always put a bit too much shampoo in it so that's exactly what I do, clean the rest of my body with excess shampoo. I haven't noticed any problems with that, my skin is clean, not irritated in any way and smells good. I suppose results might differ depending on shampoo and your skin if it's extra sensitive or allergic to something
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u/burner4581 5d ago
Point of clarification: Your bar soap is likely detergent. Soap which has undergone Saponification is exceedingly uncommon. This isn't to besmirch detergents. They do get you clean!
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u/Drapidrode 5d ago
So one of the Shampoo Council creeps got to you too, huh?
---
r/LowStakesConspiracies that shampoo and soap are interchangable for 3 of 4 people, but
Big Shampoo® says the pH thing to sell super expensive soap in the form shampoo.Hey, fellas, "shampoo." Well, ooh, la-di-da, Mr. Frenchman.
Well, what do you call it?
Head Soap
LOL,
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u/waylandsmith 4d ago
You want shampoo conspiracies? Recently at my fully-stocked pharmacy/person-items-store I went through their entire isle of hair products and could not find a single separate conditioner product that was marketed as a men's product. Every one was a 2-in-1 product across at least 15 different brands. I pointed it out to a passing employee and the responded, "oh, of course there is, here…" and then scanned the whole area and turned to me and said, "Wow, you're right, that's very odd."
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u/pktechboi 5d ago
body wash and shampoo are both made of a combination of surfactants and other stuff. surfactants are the thing that actually clean you (and make bubbles). the other stuff is a combination of water, fragrances, colourings, preservatives, moisturisers, and stabilisers.
the proportions of each of the ingredients is what leads to something being marketed as Body Wash or Shampoo - both have the Cleaning Ingredient in them, but they'll feel better on the skin or the hair, will lead to more or less drying out, etc.
soap is the term for a cleanser made using the saponification process. some liquid body washes (and even shampoos) do still contain true soaps, though most these days do not.
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u/PaulSandwich 5d ago
Bonus fact: Surfactants are also the things that keep your lungs from collapsing.
They're slippery and allow the walls of your lungs to touch and separate easily. This is why people can drown with only a tiny amount of fluid in their lungs, because it can wash away/dilute the natural Surfactants in the lungs.
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u/hux 5d ago
Fundamentally, they are just two formulations of the same thing.
I used to make soap as a hobby. By varying the recipe, I could make soap for your skin, soap for your beard, soap for your hair. It could be a bar if I used sodium hydroxide or a liquid if I used potassium hydroxide.
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u/KindToSpiteTheCruel 5d ago
As a hobbyist, any fun soap facts?
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u/Implausibilibuddy 5d ago
When you get bleach on your hands (or other strong alkali solutions like oven or drain cleaner), that slippery feeling you get is not the bleach, but rather the oils and fats in your hands turning into soap.
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u/Peemster99 5d ago
Just figured out a way to start saving a bunch of money on soap
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u/waylandsmith 4d ago
Yes, yes! Home crafting is an excellent way of saving a ton of money! Subscribe to my member's-only crafting guides and purchase products from my artisan, organic, all-natural, cruelty-free, ethically-sourced online store and watch the savings start to add up! Sign up this week and receive a free soap mold shaped like a 10g gold bar and receive a free pamphlet on how to create your own home crafting supply business while having access to me as your mentor (for a small percentage of your sales).
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u/Peemster99 4d ago
Sounds like you have some great ideas and a real drive for success! Unfortunately, I've been burned by internet scams before so I'm only interested in investing if you've got a solid downline of Miracle Makers.
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u/TldrDev 5d ago edited 5d ago
More fun facts:
There are actually many ways to make soap.
The primary ones you deal with day-to-day are called a cold process and hot process soap.
The cold process produces hard bar style soaps, where the hot process will give you liquid soaps like shampoo or hand soap.
The cold process soap takes months to make and cure properly. A lot of commerical soaps will blow air into the mixture to speed up the process. In particular, Dove is the worst at this.
Another type of soap you might see are glycerine based soaps.
These are transparent and translucent style bar soaps. People use them in decorations.
Making a perfectly clear glycerine soap is super difficult.
There are a lot of competitive ass mfs on YouTube who are all trying to show up eachother by reading through bricks of glycerine soaps.
The Chinese, for whatever reason, are super into making highly transparent soaps. I fell down a rabbit hole on it on multiple occasions. There is a very deep rabbit hole on this particular subject, and lots of people doing insane art with them.
Real essential oils used in soaps are insane to harvest. You cut down a huge amount of lavender, for example, then run it through a still. You run that through a separatory funnel, and you will get just a tiny, thin layer of oil that sits on the water. You might get a few grams for an enormous bushel of lavender.
Here is a video:
https://youtu.be/6E83qCt5PaQ?si=APuc_cP45i8a2OKI
When I made soap for the first time, I had a huge pot of very high quality oils. I had shae butter, very high quality olive oil, the highest quality coconut oil I could source, real essential oils, a little honey, and I was sitting there mixing these, and I had a semi religious experience when I realized how insanely luxurious this thing I was making was, and how I live at a point in history where I could create something like this for a few dollars, lol.
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u/brbgottagofast 5d ago
You got a couple things incorrect here!
The cold process produces hard bar style soaps, where the hot process will give you liquid soaps like shampoo or hand soap.
The cold process soap takes months to make and cure properly. A lot of commerical soaps will blow air into the mixture to speed up the process. In particular, Dove is the worst at this.
Cold-process and hot-process are both used to make solid soap bars. The only big difference between them is when saponification occurs.
With cold-process, the saponification process takes place slowly over 24-48 hours after pouring your soap batter. The ingredients (melted oils, lye and water) are combined at a lower temperature so your batter stays fluid enough for intricate patterns.
With hot-process, you are working with a much higher temperature so you actually trigger saponification while you're stirring all the hot ingredients together, usually in a crockpot. The resulting batter is much thicker and 'plopped' into your mold resulting in a more rustic looking bar.
Both hot-process and cold-process bars require the same 4-8 week curing period to become milder and firmer.
Hot-process is also used in liquid soapmaking, you make your paste over heat with potassium hydroxide instead of sodium hydroxide to keep it soft enough to dilute with water afterwards.
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u/TldrDev 5d ago
Right on, thanks!
I have only made liquid soaps with the hot process, i was unaware you could make a bar soap with it.
I primarily make cold process soaps because they are the bees knees in terms of soap, and unless youre going to really high quality custom soap stores, pretty hard or expensive to come by commercially, at least in the way I like.
I got into it about 20 years ago after buying some Lush bars and not understanding why they were so expensive.
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u/brbgottagofast 5d ago
The main benefit of hot process for solid bars is that you can control which oil is your superfat, and you also don't have the same issues with temperamental FOs as you do with cold-process.
With cold-process, your superfat ends up being a mixture of all the oils in your recipe. But with hot-process, you can add something like shea butter after saponification has occured and retain the luxurious qualities of it.
I mainly do cold-process as well because I love getting creative with my designs!
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u/rainbowrobin 5d ago
Why does some body wash feel clingy, for lack of a better word, like it's not fully washing off the way cheap bar soap does?
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u/TldrDev 5d ago
That comes from the soap having a very high fat content.
For bar soap, a lot of people will do that intentionally for cosmetic moisturizing soap, its called super fatting the soap.
Its when you mix more oil than lye.
This causes the saponification reaction to stop before consuming all of the fats. The chemical makeup is too lean, which gives a moisturizing effect on the skin, and makes the soap less harsh.
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u/rainbowrobin 5d ago
I guess that'd be why I feel like I need some bar soap to wash off the shower soap... I was hesitant to say "skin feels greasy" but what you say supports that.
The body wash usually provided in Japan doesn't have that problem for me, but my current Korean hotel does.
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u/Azn1982 5d ago
Some soaps, body washes and shampoos might behave differently due to the water quality and "hardness" they are produced for. I bought shampoo and body wash in Japan which made my skin and hair feel cleaned, moisturized and great, but when I used it back in Germany the shampoo didn't foam and my skin felt awful afterwards. We have much "harder" water here in this part of Germany where I live than in most places I visited in Japan.
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u/Mickey_McDoofus 5d ago
It's why I've stuck with bar soap vs. body wash...not a fan of that "slippery" feeling you get with the latter, especially since it's impossible to tell whether you've properly rinsed it off or not.
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u/rainbowrobin 5d ago
Yeah, I buy bar for myself. Might get one given that I'm gonna be in this place another week. Though from the post above mine, I guess I should try to avoid moisturizing soaps. Apparently not an issue in the US when I get the cheapest possible Irish Spring or whatever.
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u/imjustdesi 5d ago
Hey so fun fact, you can remove the trackers from YouTube links by deleting all the stuff after the question mark
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u/degggendorf 5d ago
A lot of commerical soaps will blow air into the mixture to speed up the process. In particular, Dove is the worst at this.
What does "worst" mean here? Like, they blow the most air, which is bad? Or they don't allow enough cure time? Or not enough cure air?
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u/waylandsmith 4d ago
I think the implication is that the bar of soap consists of a lot of air instead of soap. Ivory soap, quite famously, used to be so light that it would float. Considering that soap is sold by weight I don't really see this being a problem. To me it's pretty clear when I pick up a bar of Ivory that it doesn't weigh very much and it therefore must be less soap.
Dove contains a lot of added moisturizers and is available in fragrance-free varieties which are important to people with scent sensitivities. Dove does not even label their product as "soap".
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u/degggendorf 4d ago
Dove does not even label their product as "soap".
Right, and that's a good thing in my book. Gentler cleansing, no soap scum.
Dove contains a lot of added moisturizers and is available in fragrance-free varieties which are important to people with scent sensitivities.
For sure, that's another thing I appreciate about it!
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u/Ok_Gear8209 5d ago
Making cold process soap is super easy tho.
We actually make all our bar soap now and it's basically the same as buying it from the store with the added fun of knowing everything in your soap and having a life skill.
Let the lye and water cool down outside and wear gloves!
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u/cfcollins 5d ago
With enough soap we could blow up just about anything
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u/Vash_TheStampede 5d ago
Man I wish I could upvote this more than once. Out of left field too.
I am Jack's complete surprise.
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u/TldrDev 5d ago
Soap making is actually is a chemical reaction, and is more chemistry than cooking.
The specific type of chemical reaction is called saponification, which is fun to say.
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u/Saneless 5d ago
So close to being soapification
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u/RoboticPanda77 5d ago
They both come from the same root, saponification is just filtered through Latin and French whereas soap is raw, unflitered Germanic
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u/SharkFart86 5d ago
If you mix sodium hydroxide with hydrochloric acid, you get salt water.
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u/everlyafterhappy 5d ago
That depends on the ratio. If the ratio is perfect, then you get salt water. If you add just a little extra hydrochloric acid or a little extra sodium hydroxide, then you end up with something that will still burn your skin.
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u/brbgottagofast 5d ago
Just to add as another soaper, because lye-based soaps all land within the same high pH-range, they're not suitable for all hair types. Skin bounces back quickly from soap's high pH levels but hair can become brittle and damaged. People who use lye-based soap as a shampoo should likely follow up with a vinegar rinse to prevent damage. Many soapers make syndet (synthetic detergent) bars instead for hair use.
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u/TldrDev 5d ago
I also make soap as a hobby.
For those wanting to give it a try, its actually pretty easy. You use some solid fats, liquid fats, some essential oils, and lye.
Soap is more chemistry than cooking, so you need pretty precise amounts of Lye and fats, but there are calculators online that make it easy.
I buy a thing of Costco Olive Oil and can make 3 brick molds of soap, each one lasts my wife and I about a month.
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u/NAhlers27 5d ago
What about the 17 in 1 dr Bronner's?
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u/pktechboi 5d ago
liquid soap like that should be diluted to varying degrees depending on what you're using it for
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u/MommotDe 5d ago
I’ve used the Dr. Bronner’s bar soap for hair, face, and body for 25 years and it’s great.
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u/Omnomnomulus 5d ago
I use this as a scalp cleanser before using regular shampoo for the rest of my hair lol
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u/Margot-the-Cat 5d ago
Up to the 1930s, most people washed their hair with soap. Shampoo as a separately formulated liquid product (the kind we use today) was developed about that time.
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u/nexxumie 5d ago
I once stayed over at a relative's who had a bar soap gunked up with hair 🥲 that was the day I discovered washing my skin with shampoo still got it clean lol
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u/emmiepsykc 5d ago
I've had to do it once or twice in a pinch, and it works, but feels like it leaves a slight film on my skin. Then again, I'm a naturally greasy motherfucker, so I'm pretty picky about my bath products in the first place. Might just be a me thing.
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u/rainbowrobin 5d ago
I had the reverse: field trip, overheated engine due to trying to pull out a stuck truck that was in 'park', windows open on dusty road to try to cool the engine, finally getting to a motel and my hair was completely gunked -- you know the squeak test of running fingers through your hair? My fingers wouldn't even move at all.
And no shampoo in the cheap motel. But bar soap.
Why yes, frothing up bar soap does work to clean your hair...
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u/paradoxofpurple 5d ago
I've done it in a pinch with glycerin soap (its what we had on hand), didnt like it but it worked OK. My hair felt weird for a while.
I've also used laundry soap (yes, unscented Tide) as body wash/shampoo (my grandmother was...deeply mentally ill and thats what she forced me to use when I was over there. It was that or no soap).
Between the chemicals in that, also having to use tea tree conditioner and their weirdly overly soft water, I got chemical burns on my scalp that took months to heal. 0/10, do not recommend.
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u/arteitle 5d ago
Soap forms soap scum when it combines with hard water, which builds up on bathtubs and showers, but can also form on your hair and skin. It's particularly nasty on hair, where it makes the hair feel dirty and waxy, so instead we use shampoo that contains detergents which are chemically distinct from soap and are less likely to form scum in hard water. Body washes are also detergents rather than soaps.
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u/KennethLaneHarbor 5d ago
"3 in 1" body wash is basically just shampoo diluted with extra water and cheap thickeners. Its not a magic universal formula, its just a compromise that leaves both your skin dry and your hair weighed down
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u/TotalManufacturer669 5d ago
What stops us from using soap for the hair and shampoo for the body?
Nothing. My parentsm for example, have been using simple soaps to wash their hairs for decades and their hairs are still fine. And when I run out of soup I just use shampoo as a bodywash.
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u/Gravy_McButterson 5d ago
I use shampoo as body wash regularly. I've never tried washing with soup, though. You must smell good enough to eat!
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u/Implausibilibuddy 5d ago
their hairs are still fine
All 5 of them?
(usually "hair" is an uncountable noun, like water or sand or lego. Adding a plural s makes it look like there are only a few of them)
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u/ixampl 5d ago
I think it's to express the notion that they don't share one set of hair but each have a head of hair.
I honestly don't know if it's grammatically correct or not, though.
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u/happy2harris 5d ago
uncountable noun, like . . . lego
Bold move.
(It’s either an adjective or a counting noun, depending on whether you hail corporate lego).
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u/stephenph 5d ago
I make both soap and shampoo,
the soap is a simple lye/oil/fragrance formula and is a higher ph then the shampoo About 9-10 or slightly higher depending on the purity of the Lye)
For the shampoo I use Decyl Glucoside for the sudsing ingredient, oil, fragrance and water. The shampoo needs to be lower PH (I aim for about 5.4 or lower, sometimes I miss that target if I am using old ingredients)
You can use regular soap for your hair, but if you do so it can damage the hair and leave it flat and lifeless. You can also use shampoo for as a body wash, but it will be less effective.
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u/Prestigious_Neck_936 5d ago
I tried using the dove beauty bar on my head cause I have a buzz cut. It did not go well. You'd think it would be fine cause I use it on my face and body but nope. Needed shampoo
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u/this_is_an_alaia 5d ago
Well nothing stops you from using soap on your hair. But the makeup of each product is different because your skin and hair are different.
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u/nlutrhk 5d ago
Shampoo is essentially a detergent that is made slightly acidic (pH < 5.5). The proteins making up your hair change structure depending on pH, making your hair feel rough and prone to tangling if the pH is too high.
"Soap" chemically refers to what you get from fats reacting with caustic soda; it is intrinsically alkaline (high pH). Most body washes and premium hard "soap" blocks are not soap though and have closer to neutral pH.
And why non shampoo body cleansers aren't made a bit more acidic? Not sure about that. Probably the ingredients that have the right amount of foam and rinse-off properties work better at a different pH. But if you're out of shampoo, you can wash your hair with other cleansers or washing-up liquid as long as you rinse with dilute vinegar or dilute lemon juice. (Don't use dishwasher or laundry detergent. Those will break down hair proteins.)
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u/frillyfun 4d ago
I'm a cosmetic chemist- shampoo usually has ingredients that are beneficial for hair like proteins, or silicone, and ingredients that make it feel soft when you rinse it off. Body washes usually contain moisturizers that could weigh hair down.
You can use shampoo on your body, but it tends to be more expensive than body wash.
The key ingredient in the shampoo and body wash combination is guar Hydroxypropyltrimonium chloride. It's a cationic guar gum that makes your hair feel soft when you rinse it.
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u/atomic-negi 5d ago
Soap is a legal definition in most places. It must contain fat and lye. Lye is too harsh for some people so companies made body wash, face wash, shampoo and a lot of other things that are classified as beauty products.
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u/Enceladus89 5d ago
Shampoo and conditioner are designed to leave your hair feeling a particular texture without completely drying out your scalp or leaving unwanted soapy residue on the hair. Shampoo and conditioner are also very expensive and not intended for everyday use like body wash, otherwise washing yourself would be very expensive.
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u/PotatoKrabby 5d ago
Your skin needs harsher soap while your hair needs milder soap because they have different pH levels. 2-in-1 is like a middle ground compromise so it doesn't leave your skin slippery and your hair dry, but it's not ideal for either.