Can You Really Wash Your Hair with Soap?

Let’s talk about the elephant in the shower: can you actually wash your hair with a bar of soap? Not a detergent-based “shampoo bar,” but real, true soap—made with oils and sodium hydroxide, like the kind we’ll make in this class.

Some people will tell you, emphatically, no. That soap is “too harsh.” That the pH is wrong for human hair. That it will destroy your scalp and leave your strands in tatters. And you know what? If you just plopped a bar of handmade soap on someone who’s used to washing their hair daily with a silicone-loaded commercial shampoo and said, “Here, good luck!”—yeah, it might not go great at first.

But here’s the full story.

Why People Love Shampoo Bars

There are a few groups of folks who find their way to using soap on their hair:

• People committed to sustainability and zero-waste living.
• Natural lifestyle lovers who prefer to avoid synthetic ingredients.
• Curious experimenters who think it’s kinda cool to wash your hair with a bar.

Honestly, I’m all three. I grew up reusing everything thanks to my Depression-era grandmother (we called her Ma!), and I’ve always leaned toward natural ingredients in my home and skincare. Plus, let’s be real—traveling with one bar that does it all is pretty darn cool.

Shampoo bars ditch the single-use plastic bottles, reduce shipping weight and waste, and give you full control over what’s going on your head. My bars are made with moisturizing oils, gentle cleansers (no detergents here), and nothing you can’t pronounce. You can use them on your scalp, your skin, even your pits if you want. It’s soap. Glorious, handmade soap.

But What About the pH?

Here’s where things get a little heated.

Soap, by its nature, is alkaline (usually around pH 9–10). Human hair and scalp sit closer to the acidic side (about pH 4.5–5.5). So critics argue that using soap disrupts the hair’s natural pH and can cause damage.

And you know what? That’s not totally wrong—if you skip a few key steps or expect instant results.

Using soap on your hair does involve an adjustment period. You’ll likely need to wash less often (I’m once a week now), and an acidic rinse—like diluted apple cider vinegar—is key, especially in hard water areas. Think of the rinse as your pH-balancing BFF. It smooths the hair shaft, helps detangle, and brings things back into balance.

It’s also important to remember that this is a wash-off product, not something sitting on your hair all day. Just like washing your body with soap doesn’t damage your skin, washing your hair with soap doesn’t have to damage your hair—especially if the recipe is made with hair-loving oils and you’re using it correctly.

The Science of Hair & Soap

Let’s dig into the science a little deeper:

• Hair structure: Hair is made up of keratin protein, and the outer layer (the cuticle) resembles overlapping scales. Acidic environments keep these scales closed, making hair smoother and shinier. Alkaline environments raise the scales, which can cause roughness or tangling—if the hair isn’t rebalanced.
• Soap pH: Cold process soap typically has a pH between 9–10. That sounds high, but remember: it’s only in contact with your hair for a short time.
• Why acidic rinses work: A vinegar rinse (ACV diluted with water, often 1 tbsp per 1 cup) brings the pH back down, smooths the cuticle, and prevents buildup—especially in hard water areas where minerals can deposit on hair strands.
• Hard water interaction: True soaps can react with calcium and magnesium ions in hard water, creating soap scum. This can leave hair feeling coated or rough if not rinsed properly. Vinegar helps prevent this, too.

Want to read more?

• Structure and Chemistry of Hair – Robbins, Clarence R.
• Cosmetic Dermatology: Products and Procedures – Draelos, Zoe Diana
• This excellent blog post by Liz, a dear soapy friend, walks through both the science and the formulation of a shampoo bar in an approachable way.

My Experience (and a Shout-Out)

I spent years trying to formulate a shampoo bar I liked. Years! I tried everything, and none of them worked for me—until I found Liz’s article. Her thoughtful breakdown of ingredients and method finally helped me unlock a recipe that made my hair happy. I’ve been using it for almost a decade on my 4-foot-long hair*, and I wouldn’t trade it for anything.

I’ve tried syndet bars too. While they might work well for some people, I found them drying, overly scented, and I had to wash more often. My shampoo soap bar? It leaves my hair clean, soft, and detangled. And I only need to wash once a week. 🙌

Bottom Line

Yes, you can wash your hair with soap—as long as you understand how it works, how to support your hair during the transition, and how to make a bar that’s kind to hair.

Next up, I’ll show you how to make my favorite shampoo bar!

*A note on my 4ft of hair: I had to cut my hair when I broke my arm in 2021 because I couldn’t take care of it. It was too heavy for a one handed gla to handle alone! It’s not quite back to it’s 4ft length as of this writing, but it’s been growing about 0.75-1 inch per month. Hurrah for my shampoo bars (along with diet and genetics…. remember, we’re making soap here, not hair growth snake oil).😉