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How to make an all-natural seaweed soap recipe from scratch using babassu oil, sea kelp, and skin-brightening essential oils. Full instructions using the cold process method and explains why seaweed is great for the skin.
I just love the smell of this soap. Lavender, rosemary, tea tree, and the slightest scent of the sea. It really clears the lungs and invigorates the mind and I can tell that this is going to be wonderful to use this winter! Being a big fan of simple natural soapmaking, I also love the color that the dried kelp and French green clay bring to this seaweed soap recipe. A soft tan that is close to the shade of some seaweeds. Each speckle of powdered kelp is surrounded by a tiny golden halo that formed as it infused into the bar during the cure time.
In this piece, I’ll introduce you to using seaweed in soap, and give you a simple way to add it as a beginner. You are perfectly able to add seaweed as instructed to practically any soap recipe though. It imparts color, a light scent, and skin nourishment.
Using Seaweed in Soap
There are several ways to use seaweed in soap, and this recipe shows you the easiest way. Powdered seaweed can also be added at trace in most cold process soap recipes. It’s best to pre-mix it in a little oil though since powdered soap additives can tend to clump, leaving blobs in your bars. Dried and powdered seaweed is usually added at up to 1 tsp PPO (per pound/454 g oils).
Dried seaweed that is not a powder can be used in soap making in at least two ways. You could also use whole, or chopped, dried seaweed as a botanical decoration for the top. I’d advise this only if you live in an area without high humidity, though.
You can also reconstitute dried seaweed in the distilled water you plan on making soap with. Warm the water up first and leave the seaweed to sit in it overnight. The next day, many of the polysaccharides in the seaweed will have infused into the water. Dip your fingers in and you’ll notice a silky and almost gelatinous texture. You can either strain the seaweed out or puree it into the water and use it to make the lye solution. One part fresh seaweed to three parts water is a good amount. If using dried, use one part seaweed to four parts water.
You can use fresh seaweed much as just described, but you can also use it (or reconstituted seaweed) to make a puree. Add the seaweed puree at trace — up to 1 Tablespoon PPO.
Foraging for Seaweed
Though this recipe calls for purchased powdered sea kelp, you can use foraged sea kelp, bladderwrack, or other skin-safe seaweed. If you choose to do so, ensure that the seaweed that you collect is from a clean beach uncontaminated by pollution, dog mess, or sewage. Collect it from below the tide line, if possible, and pick seaweed that looks healthy and plump. You don’t need much seaweed to make soap, so forage only what you need and adhere to any local laws on foraging from the beach.
If you’re unsure about which seaweed you can collect, refer to local foraging information and good books. One that I have is the Edible Seashore Handbook from River Cottage. Seaweeds that you can use in soapmaking include spirulina, sea kelp, bladderwrack, and nori. Some have been shown to give skin benefits, and others simply add color.
Once collected, rinse the seaweed thoroughly in cold water to remove sand and muck and then pat dry with a kitchen towel. After that, you can either freeze, dry, or use the seaweed fresh.
Seaweed can last up to a year frozen or dried. Refrigerated, fresh seaweed only lasts a few days. If you dry the seaweed, you can store it whole or as a powder. For a powder, grind it using a food processor, ninja blender, or similar. Sift it through a sieve to get a fine powder. And if you’re wondering about nori sheets that you’d use for sushi, yes, you can use them for soapmaking too.
Why make this Seaweed Soap Recipe
Seaweed adds some really lovely qualities to handmade soap. As a powder, it mainly adds color and scent, and also light exfoliation. As a puree (added at trace) or infusion (used for the lye solution) it can also load your bars with silky polysaccharides, making the bars even more silky than usual. Polysaccharides are what makes marshmallow extract such a silky and nourishing skin ingredient and why I use it in skin cream. To really make use of them, you should make a water infusion of the seaweed the night before. Though I don’t go through that step in this recipe, you can add it if you wish.
Seaweed is also used in skincare to help delay the signs of aging and to promote collagen production and skin healing. Studies have shown that those using bladderwrack (Fucus vesiculosus) gel on the face noticed increased elasticity and decreased skin thickness in just over a month. I’m not saying that this soap will do anything to help, but it is an intriguing idea.
Sea kelp is another group of seaweed that you can use in soap making. There are several types and I use Ascophyllum nodosum in this recipe. There are many species of sea kelp though, and you can use many of them (perhaps all?) in soap making. Containing incredible amounts of vitamins, minerals, and essential fatty acids sea kelp is often used in facials and other spa treatments. Like bladderwrack, sea kelp has been attributed to increasing skin elasticity and even helping subdue the signs of aging and wrinkles.
Seaweed Soap Recipe Ingredients
You’ve heard all about the star ingredient in this seaweed soap recipe, but there are a few more I’d like to introduce you to. This soap recipe does not use coconut oil and instead uses babassu. It’s very similar to coconut in its soapmaking properties and might be more suitable for people who have a coconut allergy. It also speeds up trace, so contributes to this soap firming up very quickly.
Clay also speeds up trace, so I use just a little to help even the color of this recipe. I did make a batch with double the amount of seaweed and clay and didn’t notice it tracing any quicker. Both are fast though, so please don’t use an immersion blender. Clay is also great for oily skin, as are the essential oils used. I share a lot more information on different types of clays (and colors!) in my piece on how to naturally color soap with clay.
Although optional, the lavender, tea tree, and rosemary essential oils work to balance skin issues. They give this seaweed soap recipe a gorgeous scent that even masks the scent of seaweed. Not completely, but enough that it’s not overpowering.
Lavender essential oil has a beautiful floral scent that blends well with rosemary and tea tree. It also has skin healing and soothing properties, which is why I use it in skin salves and lavender balm.
We use rosemary and tea tree essential oils in soap for their anti-bacterial, anti-fungal, and stimulating properties. While rosemary is wonderful for mental fatigue, tea tree helps to heal acne and other skin complaints. The scents of both are also an excellent therapy against migraines and tension, as is lavender.
Seaweed Soap Recipe
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
- 109 g Babassu oil 3.84 oz
- 91 g Mango butter 3.2 oz
Soap Making Preparation
- Ensure that your soapmaking station is set up with all of the equipment, materials, and tools you need. Pre-measure each ingredient using a digital scale. Take care to wear gloves when measuring the lye.
Make the Lye Solution
- For full information on soap-making safety and equipment please head over here. It’s important to read it before trying to make soap the first time. Put on your rubber gloves and eye protection (goggles) and set yourself up in an area with good ventilation. Under a hob, on the doorstep, or outdoors is perfect. Pour the sodium hydroxide into the water and stir with a stainless steel spoon. Be careful not to breathe in the fumes.
- Stir until the lye is completely dissolved and then add the French green clay. Adding the clay to the lye solution disperses it much better than if you add it later in the process. Stir well and leave to cool to 100°F (38°C). I tend to set the jug containing the lye solution in cold water in the sink.
Melt the Solid Oils
- In a stainless steel pan, heat the babassu oil and mango butter on very low heat until just liquefied. They’ll melt quicker than you think so don’t be tempted to turn up the heat.
Blend the Powdered Seaweed
- Powdered sea kelp is relatively fine but can clump in your bars if you add it direct. To avoid this happening, mix the powdered seaweed with 1 TBSP olive oil reserved from the recipe. Blend until smooth.
Add the Liquid Oils & Seaweed Oil
- When the solid oils are melted, take the pan off the heat and pour in the liquid oils and the sea kelp oil. If you pour the liquid oils against a spoon or spatula held just inserted in hot oils, it will help to reduce air bubbles forming in your final bars.
- Stir well and keep an eye on the temperature. You want the oils to cool to just above 100°F (38°C).
- When cooled, pour in the essential oils and stir well. It's unusual to add essential oils to soap this early, but this recipe traces quickly so you'll be glad for doing it now.
Make Seaweed Soap
- Get the mold prepared, along with the chopped rosemary. You will be working quickly from this point.
- When the lye solution and oils are both about 100°F (38°C), pour the lye solution into the pan of oils. Again, pour the lye solution against a spoon or other implement to reduce air bubbles.
- Gently but quickly, stir the contents of your pan, and do not be tempted to stick blend. This recipe traces quickly and almost immediately after stirring you'll see chunky white blobs in the pan. Keep stirring until the entire pan is a consistent creamy color and has thickened up to the texture of warm custard. This takes less than a minute and you need to work even faster now.
Mold and Cool the Seaweed Soap
- Pour the soap into your mold, and I recommend a silicone loaf mold. Create texture on the surface of the soap, decorate with pieces of rosemary, and pop the mold into the refrigerator. Leave it there for 12-24 hours.
Cut and Cure the Seaweed Soap
- Take the seaweed soap out of the refrigerator the next day but leave it inside the mold. Set it someplace on the counter and leave it there for another day to harden up a bit. Saying that, this soap hardens up relatively quickly and could be popped out of the mold much earlier. 48 hours is safer though since most of the saponification is complete by then.
- After you cut them, leave the bars someplace airy and out of direct sunlight to cure for at least four weeks. For full instructions on how to cure handmade soap, and why a minimum month for curing is important head over here
Using your Homemade Seaweed Soap
- The lather and feel of this handmade seaweed soap is fluffy and silky. The scent is a gorgeous herbal blend but you may get the faint smell of sea kelp as you use it. Using more kelp than listed in this recipe will give you darker bars that smell even more like sea kelp.
- Once made, your soap will have a shelf-life of up to two years. Check the oil bottles that you're using though — the closest best-by date is the best-by date of your soap. That's because some of that oil is free-floating in your bars as the superfat, and it can go rancid over time.
More Seaside Inspiration for You
The seaside has many treasures, both beautiful and edible, to enjoy and create with. Here are some more ideas for you to explore:
- Make Soleseife: A Seawater Soap Recipe
- Uplifting Spirulina Body Scrub Recipe
- How to make a Sea Glass Candle
- Foraging for Wild Food on the Beach
- Beachcombing for Sea Glass
- Make seaweed fertilizer for the garden