Castile soap is a vegetable-based soap derived from water, lye, and olive oil. The soap is non-toxic and biodegradable, and it cleans well as a body wash or hand soap.
If you're looking at castile soap for hair growth, here's the short answer: it won't make your hair grow. Castile soap is a cleanser, and nothing in it changes how the hair follicles under your scalp make hair.
It can wash your hair and scalp, but it's a harder match for curly hair than most shampoos. That's because soap is alkaline, meaning it has a high pH, while your scalp and hair strands are naturally acidic.
As a shampoo replacement, castile soap is potent enough to remove dirt and product buildup on the scalp. It's also strong enough to wash away your hair's natural oils, so a little goes a long way.
Like any soap, castile soap lifts sebum, the natural oil your scalp makes, off your scalp and hair along with the dirt. That’s why how much you dilute it, and what you put on your hair afterward, matter so much.
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If you want to save money on your beauty products, switching to castile soap can be great since it often costs just a fraction of commercial shampoo products.
Castile soap can be customized by adding other natural ingredients like essential oils for refreshing scents and antimicrobial properties. In this article, we'll explain what castile soap can and can't do for your hair, how to use it more gently, and who should skip it.
Key Takeaways
- Liquid Castile Soap as a Shampoo Alternative: Castile soap can stand in for shampoo, especially in liquid form, but it isn't the gentler choice. Soap has a pH of about 8.5 to 11, far above your scalp's 5.5, so it can leave your hair rough, tangled, and frizzy. For most curly hair, a sulfate-free shampoo is easier on your hair and scalp.
- DIY Shampoo Recipes with Organic Ingredients: Making your own shampoo with liquid castile soap lets you add essential oils like peppermint, tea tree, and lavender. Dilute the soap well in every recipe, and skip these recipes if your hair is dyed or highlighted.
- Apple Cider Vinegar Rinse for Balanced pH: Following a wash with castile soap, an apple cider vinegar rinse is essential to rebalance the scalp's pH level. This step is crucial for best results, as castile soap is alkaline, and the rinse helps maintain the natural acidity of the scalp and hair shaft.
- The Waxy Feel After Switching: If your hair feels waxy, sticky, or heavy after a castile soap wash, that isn't your hair adjusting. It's soap film, which forms when soap meets the minerals in hard water. Mix the soap with distilled water, and if your hair still feels coated after two or three washes, go back to a sulfate-free shampoo.
- Benefits of Pure Castile Soap Beyond Hair Care: Castile soap is versatile, functioning not just as a hair cleanser but also as a gentle body wash, face wash, and hand soap. Since one bottle covers all of these, it's an easy way to simplify your routine.
What Does Castile Soap Do For Your Hair?
Castile soap cleans your hair and scalp. That's its main job, and it doesn't make your hair grow. Here's what holds up about the other benefits people credit it with:
1. Hydrates the Scalp and Hair
Castile soap does little to hydrate your hair, since you rinse it out within a few minutes. It's made with a vegetable oil base but may also be made with olive oil, hemp oil, neem oil, and coconut oil (or coconut milk in certain specialty recipes).
Castile soap does not contain sulfates, the strong cleansers in many shampoos. But soap is a strong cleanser too, so being sulfate-free doesn’t stop it from drying out your hair. Glycerin is a byproduct of oil-based soap making, but most synthetic soaps eliminate glycerin from the end product.
Glycerin is a humectant, which means it draws water toward your hair. Castile soap keeps its glycerin, but most of it goes down the drain when you rinse. So, to actually moisturize your hair after a castile soap wash, use a conditioner.
2. Great for Soothing Sensitive or Irritated Scalp
Castile soap isn't the best choice for a sensitive or irritated scalp. It does have a short ingredient list, and unscented castile soap has no added fragrance, which helps if fragrance is what bothers your skin.
However, soap is hard on your skin’s protective barrier. A dermatology review explains that the high pH of traditional soap can make dry or eczema-prone skin worse, leaving it red, rough, and scaly. Mild cleansers called syndets (short for synthetic detergents), which most sulfate-free shampoos use, are easier on skin.
So, if you have scalp eczema or seborrheic dermatitis, the condition behind stubborn dandruff, a gentle, fragrance-free shampoo is the safer pick.
If your scalp is red, itchy, or flaking and it doesn't clear up after you stop using a new product, see a board-certified dermatologist.
3. Reduces Inflammation and Protection From Free Radicals
Castile soap isn’t a proven way to calm an inflamed scalp. Olive oil does contain oleocanthal, a compound that works against inflammation in a similar way to ibuprofen. However, that research is about virgin olive oil in your diet. Making soap turns the oil into something new, and you rinse castile soap off your scalp within minutes.
If your hair is thinning or breaking off, look for the cause first, such as tight styles, heat, or rough detangling, rather than a soap that promises to fix it.
4. Gets Your Hair and Scalp Clean
Castile soap does get your hair and scalp clean, and this is the benefit that holds up. One end of each soap molecule grabs onto oil, and the other end grabs onto water. So, when you rinse, the oil, dirt, and product buildup wash away with the water.
That's also why castile soap can leave your hair feeling dry. It doesn't stop at dirt; it takes your scalp's natural oil with it, which is why the conditioner step below matters.
Why Castile Soap's pH Matters
Castile soap is alkaline, and your scalp and hair strands are acidic, so the two don't match. pH is a scale from 0 to 14 that shows how acidic or alkaline something is. Seven is neutral, numbers below 7 are acidic, and numbers above 7 are alkaline.
Your scalp sits at a pH of about 5.5, and your hair strands sit even lower, at about 3.67. The review above puts soap, castile included, at a pH of about 8.5 to 11. A syndet, the kind of cleanser in most sulfate-free shampoos, runs about 5.5 to 7, much closer to your scalp.
So, what does that do to curls? When you wash with something alkaline, your hair strands pick up extra negative charge. Strands with more charge rub against each other more, which means more tangles and frizz. Over time, that rubbing can damage the cuticle, the thin outer layer of each strand, and lead to breakage.
Your scalp feels the high end of that range the most. Safety rules treat a pH of 10.5 or higher as irritating to skin, and some soaps go past that.
None of this means one castile soap wash will ruin your hair. It means the soap works against your hair's pH every time you use it. That's why the steps below matter so much if you use it: a lot of water, an acidic rinse, and a conditioner.
How Castile Soap Is Made
Castile soap is made by mixing plant oil, traditionally olive oil, with a strong base. Soap makers use either sodium hydroxide, which is lye, or potassium hydroxide. That reaction, called saponification, turns the oil into soap.
Because a strong base goes into every batch, every true soap comes out alkaline. Natural, organic, or homemade, it doesn't matter. No castile soap you buy or make will match your scalp's pH.
Liquid Castile Soap vs. Bar Soap
Liquid castile soap and castile bars are both true soaps, so both are alkaline. For your hair, liquid is easier to use. You can measure it by the spoonful and stir it straight into water, while a bar has to be melted first, as in the bar recipes below.
Neither one gets around hard water. Both react with the calcium and magnesium in it and leave a film on your hair, so the distilled water advice below applies to both.
How to Wash Your Hair with Castile Soap
When using castile soap to wash your hair, being gentle and precise can make the process successful and fulfilling.
However, a few mistakes can leave you feeling worse, especially with soap scum and greasy hair. Follow these steps to ensure a seamless hair care routine.
1. Dilute the Castile Soap Before Use
Castile soap is an extremely potent alkaline solution, and when used in undiluted form, it can cause abrupt pH disruptions on your scalp. You should take a small amount of castile soap and dilute it with enough purified water. Water makes the soap milder on your scalp, but it doesn’t make it acidic.
While it might appear easier to just use regular tap water, it's important to remember that tap water often contains calcium and magnesium, the minerals that make water hard. Soap reacts with them and leaves a film on your hair. Tap water can also carry chlorine.
If this is your first time, start with one tablespoon of the soap diluted with four cups of purified water. As you become more accustomed to castile soap, you may adjust the ratio according to your hair's needs.
Nevertheless, be careful with using too much castile soap. The recipes further down are stronger mixes than this, so if your scalp feels tight or itchy after one, add more water next time.
Note: Even commercial brands of castile soap purchased over the counter usually require dilution. Dr. Bronner's Soap is a popular commercial brand that uses "Dilute! Dilute! Ok!" within its labeling and marketing materials. So, please follow the directions and dilute this soap before using it.
2. Always Use a Post-Wash Acidic Rinse
Castile soap is alkaline; thus, you need a follow-up rinse with an acidic solution like apple cider vinegar or lemon juice to rebalance the natural pH on your scalp.
You can either use four tablespoons of apple cider vinegar or ¼ cup of lemon juice diluted with two cups of water. Apple cider vinegar is the better pick, since lemon juice is more acidic. After rinsing with this acidic rinse, wait for a few minutes and rinse with lots of cold water to clear the apple cider vinegar or lemon juice.
If you are using apple cider vinegar as your post-wash acidic rinse (also called an acidic conditioning rinse), your hair might hold on to the smell.
It goes away as you rinse with water, so rinse until it dissipates completely. You can minimize the scent by adding a few drops of essential oil, like lavender oil.
3. Moisturize the Scalp and Hair with Oil
After washing your hair with castile soap, use a conditioner first, then add an oil if your hair likes one. Soap leaves your hair strands with extra negative charge, and conditioners are made to cancel that charge out, which cuts down on tangles and frizz.
Some great natural oil options include jojoba, avocado, coconut, apricot, sweet almond, argan, and castor oil. Aloe vera is also a good option.
How to Use Castile Soap for Hair Growth
Castile soap itself won't grow your hair. Hair grows from follicles under your scalp, and a soap you rinse off in a minute or two doesn't change how they work. The hair growth claims come from the essential oils you can add, so here's what's known about each one in these recipes.
Peppermint Castile Homemade Shampoo
Peppermint adds a refreshing scent, and in a four-week study on mice, 3% peppermint oil grew more hair than minoxidil, a hair loss treatment sold in drugstores. That’s promising, but mice aren’t people. This recipe is also far weaker than 3%, and the peppermint rinses off with the soap instead of staying on your scalp.
Tea tree essential oil contains antimicrobial and antiseptic properties. In a four-week trial, a shampoo with 5% tea tree oil improved dandruff by 41%, compared with 11% for the same shampoo without it. This recipe has much less tea tree oil than that, so think of it as a scent and a small extra, not a dandruff treatment.
Ingredients and Directions
- 20 drops of quality peppermint oil
- 4 tablespoons of castile soap
- 20 drops of essential tea tree oil
- ½ teaspoon of virgin olive oil
- 2 cups of water
In a bottle, add the castile soap and dilute it with the water while shaking until it's well mixed. Add the oils and continue shaking the mixture to get an even blend.
You can use homemade shampoo to wash your hair and scalp. Use lemon water to rinse your scalp and hair, then moisturize with jojoba or olive oil.
Using Castile Soap for Hair Care
While you can use diluted castile soap to wash your hair, you can get more benefits by customizing the soap. Just keep each mix well diluted, and follow every wash with an acidic rinse and a conditioner.
If your skin is sensitive, patch test each recipe first. Dab a little on the inside of your elbow, wait 48 hours, and skip the recipe if your skin turns red or itchy.
Lavender Oil Castile Shampoo Bar
Almond oil is known for its softening properties and helps moisturize the scalp and hair. On the other hand, lavender is a valuable ingredient in aromatherapy for relieving anxiety and stress.
Lavender oil also helped hair grow in a study on mice, at 3% and 5% strength. If you want to try it for growth, it has a better chance as an oil you leave on and work in with a gentle scalp massage than in a bar you rinse off.
Ingredients and Directions
- 30 drops of lavender oil to add fragrance
- 4 bars of castile soap
- ½ teaspoon of almond oil
- 2 cups of distilled water
In a bowl, melt the castile soap bars using moderate heat and the double boiler method. After the soap is thoroughly melted, add the lavender oil and almond oil to make a well-mixed solution.
Pour the shampoo into a mold and let it cool down and harden into a shampoo bar. Once it hardens, you can use the shampoo bar to wash your hair and, after rinsing, apply almond oil to moisturize and add sheen to your hair.
Anti-Dandruff Castile Shampoo
Clove oil is the dandruff ingredient in this recipe. In a lab test, it slowed the growth of Malassezia, the yeast family linked to dandruff, but the yeast came from dogs’ ears, not people’s scalps.
So, if you’re fighting dandruff, the American Academy of Dermatology recommends a dandruff shampoo with an ingredient like zinc pyrithione, salicylic acid, or ketoconazole. If your hair is curly or coily, use it about once a week and keep it on your scalp.
Ingredients and directions
- 4 tablespoons or 5 bars of castile soap
- 30 drops of clove oil or 1 tablespoon of cloves powder
- ½ teaspoon grapeseed oil
- 200 ml of distilled water
If you're using liquid soap, pour the distilled water and soap into a bottle and shake well to mix. Add the other ingredients and shake well until you get an even mix.
If you're using castile soap bars, melt the soap in a microwave to get a clear liquid, then add all other ingredients and mix well. Pour the mixture into molds and allow it to set.
Rosemary Lemon Castile Shampoo For Extra Sheen
This bar gets its sheen from the almond oil, while the rosemary and lemon oils add a fresh scent.
Rosemary is the one with hair growth research behind it. In a six-month trial with 100 people with hereditary hair loss, rosemary oil on the scalp worked about as well as 2% minoxidil. Neither group had more hair at three months, though. So, if you try rosemary oil for growth, give it six months, and use it as an oil you leave on rather than in a soap you rinse off.
Ingredients and Preparation Directions
- 3 tablespoons of powdered rosemary leaves
- 6 bars of castile soap
- 2 tablespoons of almond oil
- 5 drops of essential rosemary oil
- 12 drops of essential lemon oil
In a heatproof bowl, put the castile soap bars and melt on low heat using the double boiler method. Keep the heat on until the soap melts into a clear liquid.
Add the powdered rosemary leaves and stir the mixture.
Add the lemon oil and rosemary oil while stirring the mixture, and finally, add the sweet almond oil to the solution. Pour the blend into suitable molds and allow some time to set and harden into a shampoo bar.
You can use the shampoo bar to clean your hair and scalp, but follow up with a rinse massage with some almond oil to lock in the moisture.
Is Castile Soap Good for Hair Care?
For most curly hair, castile soap isn't the best everyday cleanser, mainly because of its pH. Your experience also depends on your water and how you prepare the soap. If you only have hard tap water, then castile soap recipes may not be a good idea for you.
It might leave you with an ugly mess on your hair, but if you use distilled water, you can give castile soap a try.
It's important to note that poor water quality, especially if you live in an area with hard water conditions, can cause hair damage. Read this article to learn more.
Unlike most DIY hair care products, castile soap requires careful use and adherence to specific conditions for it to work. Similarly, steer clear of castile soap if you have dyed hair, because the high pH can make your color fade faster.
Making the transition from commercial shampoos to castile soap shampoos is not always easy. And it may not be ideal for everyone since different hair types will react differently.
In fact, your immediate observation may discourage you from using castile soap. Your hair might feel unclean and heavy. That's usually soap film from the minerals in your water, not your hair getting used to a new routine, so it won't go away on its own.
Most importantly, pair the shampoo with a conditioner to make the transition easier.
So, who can still use castile soap on their hair? It's a reasonable occasional wash if your water is soft or you mix it with distilled water, your hair isn't dyed or highlighted, and your scalp isn't sensitive. It's also handy when you're traveling, since one bottle covers your hair and your body.
If that's you, use the dilution in step 1, follow with the acidic rinse, and finish with a conditioner. Then watch how your hair feels over your next two or three wash days. If it comes out rough, tangled, or coated, go back to a sulfate-free shampoo for your regular wash days.
Wondering about other natural cleansers? African black soap is a true soap too, so it’s alkaline in the same way. Soap nuts and shikakai are different. They clean with saponins, plant compounds that foam, and they aren’t made with lye.
Original Curl Centric chart
After a castile soap wash: normal, or time to stop?
Find the row that matches how your hair and scalp feel after you wash with castile soap, then start with the last column.
| What it is | What you notice | Why it happens | What to do first |
|---|---|---|---|
| A clean wash | Your scalp feels clean, your hair feels soft, and your curls clump the way they usually do. | The soap was well diluted, your water was soft, and the acidic rinse and conditioner did their part. | That’s normal. Keep the same dilution, and keep using the acidic rinse and a conditioner after every wash. |
| Soap film | Your hair feels waxy, sticky, or heavy and looks dull, even after a long rinse. | Soap reacts with the calcium and magnesium in hard water and leaves a film on your hair strands. | Mix the soap with distilled water. If your hair still feels coated after two or three washes, switch to a sulfate-free shampoo. |
| Frizz and tangles | Your hair feels rough or squeaky, and it tangles and frizzes more than it does after your usual shampoo. | Soap’s high pH gives your hair strands extra negative charge, so they rub against each other more. | Add more water to the soap, use the acidic rinse, and detangle only when your hair is full of conditioner. |
| Faded color | Your dye or highlights look duller or lighter sooner than they usually do. | Alkaline soap swells your hair strands and lifts the cuticle, their outer layer, so dye washes out more easily. | Stop using castile soap on your colored hair, and go back to a shampoo made for color-treated hair. |
| Scalp irritation | Your scalp feels tight, itchy, or sore, or it looks red or flaky after you wash. | Soap’s pH sits far above your scalp’s, and the essential oils in a recipe can irritate your skin too. | Stop using it. If your scalp doesn’t settle down after you stop, or the problem keeps coming back, see a board-certified dermatologist. |
Castile soap can’t make your hair grow or stop it from falling out. If you’re shedding more than usual, or your hair is thinning or coming out in patches, see a board-certified dermatologist.
Can You Use Castile Soap as a Body Wash?
Yes, castile soap works well as a body wash, and your skin handles it better than your hair does. Washing does push your skin's pH up, but it drifts back down within a few hours.
If your skin is dry, itchy, or prone to eczema, a gentle syndet body wash is the better choice for the same pH reasons. And keep castile soap out of your eyes, since it stings.
Hair Care Mistakes To Avoid With Castile Soap
Castile soap is a simple, natural beauty solution that is safe to use for most people. However, some things could go wrong if you are not careful. Avoid the following mistakes when using castile soap for your hair.
Don't Use Castile Soap on Dyed Hair
As incredible as it may seem, hair dyes can compromise your hair, and bleaching affects the structural integrity of your hair. According to a review of hair cosmetics, bleaching and hair coloring wear down the inner layers of each strand, which weakens it and makes it more likely to break.
As such, it is essential to use only shampoos that are not too harsh on the weakened hair.
Castile soap is highly alkaline, and alkaline products swell your hair strands and lift the cuticle, the outer layer that protects the inside of each strand where the color sits. That makes it easier for dye to wash out, so dyed or highlighted hair can fade faster.
Don't Use Hard Water to Dilute Castile Soap
It would be best if you didn't use concentrated castile soap directly on your hair. Always dilute a small amount of soap with water.
Hard water has a lot of calcium and magnesium in it. Soap reacts with those minerals and forms soap scum, the same film you see on a shower door. On your hair, that scum is hard to rinse out, and it can leave your curls dull and tangled.
Instead, use distilled water to dilute the soap, and you won't have to use too much vinegar to rinse off the soap.
Castile Soap Shampoo Recipe
Ingredients and Directions
- ¼ cup of castile soap
- ½ cup of distilled water
- 40 drops of essential oils, like lavender oil, tea tree oil, and rose oil
- ½ cup of carrier oil like olive oil, avocado oil, jojoba oil, almond oil, or argan oil
In a clean bottle, pour in the castile soap, then add the distilled water and shake vigorously to mix well. Add the essential oils and carrier oil, and continue shaking until you get an even blend.
Anytime you want to use the Castile shampoo, use a quarter of the prepared volume from this recipe, and stir it into a cup or two of warm distilled water before you pour it over your scalp. However, if you are switching to natural shampoo from long-term use of commercial shampoos, patience is necessary.
Your hair may feel oily, stiff, heavy, sticky, or very dry for the first few washes. Stiff, sticky, or heavy hair is usually soap film rather than a detox, and dry hair is the soap's high pH at work. If it hasn't improved after two or three washes with distilled water, the acidic rinse, and a conditioner, castile soap isn't the right cleanser for your hair.
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Castile soap has made waves in the curly hair community as a DIY beauty product regardless of hair type. However, if it's not used in the right way, it will surely leave you with a greasy mess that looks terrible on your hair.
Often, this is caused by excess minerals in hard water, and the only way to avoid the greasy scum is by using distilled water.
Overall, very few hair care products can be as versatile as castile soap. Besides cleaning your hair and scalp effectively, castile soap can be customized with the oils you like.
If you want to try it, start with the diluted wash in step 1, use distilled or soft water, and follow it with the acidic rinse and a conditioner. If your hair comes out rough, tangled, or coated, a sulfate-free shampoo is the gentler choice for your regular wash days.
