Is Castile Soap Good for Hair? 4 Shampoo Ideas Based on Castile Soap

Finding a natural, eco-friendly shampoo that genuinely works with your hair can be a challenge. Castile soap – a plant-based, biodegradable soap traditionally made from olive and other vegetable oils – has become popular because it’s gentle, versatile, and free from many synthetic ingredients found in conventional shampoos. Dermatology experts describe Castile soap as a natural, nontoxic cleanser made without synthetic detergents or foaming agents, which is why it’s often recommended for people who prefer simpler formulations. You can see this outlined in more detail in this overview of Castile soap from Cleveland Clinic.

In this blog post, we’ll look at when Castile soap can be a good option for hair, how to tweak it for different hair types, and 4 simple DIY Castile soap shampoo ideas. Because Castile soap is more alkaline than most hair and scalp-friendly products, it does need a bit of care and balancing to avoid dryness or a rough feel. Hair and scalp tend to sit around pH 4.5–5.5, while Castile soap solutions can be closer to pH 8–9, so it’s important to dilute it well and pair it with more acidic rinses or hydrating ingredients. You’ll sometimes see this pH mismatch flagged in practical guides warning that undiluted Castile soap can leave hair feeling “squeaky” or rough over time if not followed with an acidic step, as discussed in this look at Castile soap shampoo and hair pH.

If you’re also rethinking the rest of your shower routine, you might find it helpful to explore our guides to chemical-free, eco-conscious soaps and biodegradable soap and shampoo bars for sustainable travel alongside these hair-focused recipes.

Why Use Castile Soap for Hair?

Castile soap is a fantastic base for homemade shampoo because of its:

1. Natural ingredients – Castile soap is made from plant-based oils such as olive, coconut, or jojoba, and doesn’t rely on synthetic detergents, sulphates, or foaming agents. Clinical and dermatology summaries of Castile-type soaps note that olive-oil-based cleansers can be gentler on sensitive skin than some harsher surfactants, which is why you’ll often see them suggested as a milder option. This medical overview of Castile soap gives a good, concise summary of how these soaps differ from standard cleansers.

   
   

2. Eco-friendly properties – Castile soap is biodegradable, typically vegan, and often packaged in recyclable or post-consumer recycled bottles. That makes it attractive if you’re trying to reduce plastic and choose simpler ingredients that break down more easily in the environment.

   
   

3. Customisability – Because it’s a simple, concentrated liquid soap, Castile works well as a base to blend with other hair-friendly ingredients such as aloe vera gel, oils, hydrosols, or essential oils. Aloe vera, for example, has been noted in dermatology sources to contain fatty acids and vitamins that may help strengthen hair and calm an itchy scalp, as outlined in this overview of aloe vera’s benefits for hair.

   
   

4. Affordability and versatility – A single bottle goes a long way once diluted, and you can use it not only in hair recipes but also for body wash and even around the home. If you’re trying to streamline your routine and reduce the number of separate products you buy, a Castile base can be a practical way to do that.

One important caveat: Castile soap is naturally alkaline, while your hair and scalp prefer a slightly acidic environment. Stories and reviews about using Castile soap as shampoo often highlight that products with a pH higher than 7 can raise the cuticle, making hair feel rough, frizzy or “squeaky” if used without an acidic follow-up. You’ll see this discussed in practical guides such as this deep dive on Castile soap shampoo and hair pH and in stylist-led explainers on why unbalanced alkaline products can cause cuticle damage over time.

That’s why many people find Castile soap works best on hair when it’s diluted and followed by an acidic rinse (such as apple cider vinegar in water) or combined with soothing, hydrating ingredients in the recipe itself.

4 DIY Castile Soap Shampoo Ideas

1. Basic Castile Soap Shampoo

This simple recipe is perfect for those new to Castile soap-based shampoos. It gently cleanses the hair without stripping it of natural oils.

Ingredients:

•  1/4 cup liquid Castile soap (unscented or scented)

• 1/4 cup distilled water

• 1 tablespoon carrier oil (e.g., jojoba, argan, or almond oil)

• 10 drops of essential oil (optional, for fragrance)

Instructions:

   1.    Combine all ingredients in a bottle.

   2.    Shake well before each use.

   3.    Apply a small amount to wet hair, lather, and rinse thoroughly.

Best For: Normal to oily hair.

2. Moisturising Castile Soap Shampoo for Dry Hair

Dry hair needs extra hydration, and this recipe adds aloe vera and glycerin for a moisture boost.

Ingredients:

   •    1/4 cup liquid Castile soap

   •    1/4 cup aloe vera gel (pure)

   •    1 tablespoon vegetable glycerin

   •    1 tablespoon coconut oil (melted)

   •    5 drops lavender essential oil

Instructions:

   1.    Mix all ingredients in a reusable bottle.

   2.    Shake gently to combine.

   3.    Apply to damp hair, focusing on the scalp, and rinse thoroughly.

Best For: Dry or curly hair, especially if you find traditional sulphate shampoos too stripping. Aloe vera is often highlighted as helpful for calming an itchy, flaky scalp and supporting hair strength; a 1998 study on seborrheic dermatitis (dandruff) found that aloe helped reduce inflammation and scaling, which is why it frequently appears in soothing scalp treatments and shampoos. You can read a simple summary in this piece on aloe vera’s benefits for hair and scalp.

3. Clarifying Castile Soap Shampoo for Oily Hair

Oily hair can benefit from a clarifying shampoo to remove excess sebum and product buildup.

Ingredients:

   •    1/4 cup liquid Castile soap

   •    1/4 cup apple cider vinegar

   •    1/2 cup distilled water

   •    5 drops tea tree essential oil

Instructions:

   1.    Combine the ingredients in a bottle and shake to mix.

   2.    Use as needed to cleanse the scalp and hair thoroughly.

   3.    Follow with a conditioner or diluted apple cider vinegar rinse to restore pH balance.

Best For: Oily or fine hair, and occasional clarifying if you use a lot of styling products. Tea tree oil has been studied in a 5% shampoo for dandruff and showed significantly greater improvement than placebo in flaking, itch and greasiness, which is why it’s often chosen for oily or problem scalps. That clinical trial is summarised in this PubMed abstract on tea tree oil shampoo for dandruff.

4. Strengthening Castile Soap Shampoo for Damaged Hair

This recipe incorporates protein-rich ingredients to strengthen and repair damaged hair.

Ingredients:

   •    1/4 cup liquid Castile soap

   •    1/4 cup coconut milk (unsweetened)

   •    1 tablespoon honey

   •    5 drops rosemary essential oil

Instructions:

   1.    Mix all ingredients in a bottle.

   2.    Shake well and apply to wet hair.

   3.    Rinse thoroughly and follow with a natural conditioner.

Best For: Damaged, coloured, or chemically treated hair needing a little extra care. Coconut milk adds richness, while honey attracts moisture to the hair shaft. Rosemary essential oil is particularly interesting here: a 2015 randomised trial found that a rosemary oil solution performed similarly to 2% minoxidil for androgenetic alopecia after six months, with both groups seeing increased hair counts. You can see the details in this study comparing rosemary oil and minoxidil.

Although that trial looked at leave-on treatment rather than rinse-off shampoo, it helps explain why rosemary oil is frequently included in products aimed at supporting scalp health and hair density.

Tips for Using Castile Soap as Shampoo

Tips for Using Castile Soap as Shampoo

1. Dilute it well – Castile soap is concentrated and can be drying if used undiluted, especially on fine or porous hair. Always dilute it with water or other hydrating ingredients like aloe vera gel or coconut milk.

2. Follow with an acidic rinse – To help close the cuticle and bring the pH closer to what hair prefers, follow with an acidic rinse. A simple mix of 1 part apple cider vinegar to 4 parts water is a common starting point. Hair-care writers often note that apple cider vinegar, which sits around pH 2–3, can help smooth the hair shaft and add shine by lowering pH; you can see this discussed in this Healthline overview on ACV for hair and in a 2024 evidence review on ACV and scalp pH.

3. Use sparingly – A small amount is usually enough; using more won’t necessarily clean better and might make hair feel coated or dry. Start with a small amount of diluted mixture and adjust based on how your hair feels.

4. Test it first – If you’re unsure how Castile soap will work for your hair, try it on a small section first or use it once a week alongside your usual shampoo. Keep an eye on how your hair and scalp feel over several washes before committing fully.

   
   

Is Castile Soap Right for You?

Castile soap works well for some hair types but not for everyone. Because it’s alkaline, it can leave the cuticle more open if it isn’t followed with an acidic step, which may make hair feel rough, tangled or dull over time — especially on colour-treated or very porous hair. Many stylists and formulators recommend that people with very fine, bleached, or fragile hair use pH-balanced, purpose-made shampoos more often, and treat Castile-based recipes as an occasional option rather than a daily staple.

Water type matters too. If you have very hard water, the minerals (mainly calcium and magnesium) can react with soap to form residue, leaving hair feeling waxy or coated and creating more soap scum on bathroom surfaces. Articles explaining the difference between hard and soft water, such as this summary of hard water vs soft water and their impact on skin and hair, note that hard water often makes it harder to rinse products fully and can contribute to dryness and buildup over time.

If you find that Castile soap leaves your hair coated or dull even with dilution and an acidic rinse, it may be worth looking at other gentle, sulphate-free shampoos or solid shampoo bars designed with hair-friendly pH in mind, while still keeping the rest of your routine as natural as you’d like. Our round-up of chemical-free, eco-conscious soaps and eco-friendly bath products in the UK can give you more ideas for building a lower-toxin bathroom shelf overall.

If you’d like to experiment with these recipes, starting with a good-quality Castile base makes all the difference.

1. Dr Bronner’s Pure-Castile Soap

Dr Bronner’s Pure-Castile Liquid Soap is one of the best-known options, made with organic plant oils and packaged in 100% post-consumer recycled plastic. The unscented “Baby-Mild” version, in particular, contains no added fragrance and extra olive oil, making it a popular choice for sensitive skin and DIY recipes.

2. The Humble Shepherd Castile Soap

At The Humble Shepherd, we create premium, handmade Castile-style soaps that work beautifully for body and hair care recipes. Our bars are crafted with organic plant oils, biodegradable ingredients, and low-waste, eco-conscious packaging. They’re designed to be gentle enough for regular use while still giving a satisfying, creamy lather.

• All our soaps are vegan and cruelty-free, so they fit easily into a kinder, more ethical routine.

• They’re suitable for hair, skin, and gentle household cleaning when diluted correctly.

• We offer a choice of lightly scented or unscented options so you can decide whether to add your own essential oil blends or keep things simple.

You can browse our handmade Castile soap collection to choose the base that best suits your hair and skin needs, or join the Shop Now waitlist if you’d like to be first to hear when new batches and scents are released.

Final Thoughts

So, is Castile soap good for hair? The honest answer is yes - for some people and in the right way. When it’s properly diluted, balanced with an acidic rinse, and customised to your hair type, Castile-based shampoo can offer a simple, low-ingredient alternative to many commercial formulas. It’s also a flexible way to experiment with natural actives like aloe vera, tea tree, or rosemary in your own blends, each of which has some early research or clinical work behind its use for scalp comfort or hair density.

Whether you’re looking for more hydration, occasional clarification, or a gentle option on days when your scalp feels sensitive, the 4 DIY Castile soap shampoo ideas above give you a starting point you can tweak over time. If you’d like more ideas on building a greener routine, from bar soaps to low-waste bath swaps, you can explore our wider soap and skincare blog for inspiration and how-tos.

When you’re ready to get started, choose your base from our handmade Castile soap collection, join the Shop Now waitlist if you love being first in line for fresh batches, and then start customising your shampoo to match your hair, your water, and your values. Switching to Castile soap, even part of the time, can be a simple, practical step towards a gentler, more sustainable hair care routine.