Seaweed Soap Recipe with Skin-Nourishing Sea Kelp

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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 formed as it infused into the bar during the cure time.

In this piece, I’ll introduce you to using seaweed in soap recipes and give you a simple way to add it as a beginner. You can 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 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).

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 skin #soaprecipe #soapmaking #seaweed

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 in 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.

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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 skin #soaprecipe #soapmaking #seaweed
Seaweed infusing in cool water. You can use the silky water to make a lye solution

You can use fresh seaweed as described above, but you can also use it (or reconstituted seaweed) to make a puree. Add the seaweed puree at trace at up to one Tablespoon per pound of soaping oils.

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 do so, ensure that the seaweed 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 local laws on foraging from the beach.

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 skin #soaprecipe #soapmaking #seaweed
Seaweed growing on the beach near my house

If you’re unsure 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.

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 skin #soaprecipe #soapmaking #seaweed
Seaweed adds silkiness, color, light exfoliation, and potential skin benefits

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 them even more silky than usual. Polysaccharides make marshmallow extract such a silky and nourishing skin ingredient, and that is 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.

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 skin #soaprecipe #soapmaking #seaweed
If you double the amounts of clay and seaweed, your soap will be darker

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.

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 skin #soaprecipe #soapmaking #seaweed
French green clay and sea kelp give this soap its color

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 with 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 in this soap recipe. I share a lot more information on different types of clays (and colors!) in my piece on how to naturally color soap with clay.

Seaweed has many uses in skincare recipes and in the garden

Essential Oils in this Soap Recipe

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 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 recipes 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.

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:

Seaweed Soap Recipe

Lovely Greens
Seaweed soap recipe that makes 5-6 bars using the cold-process method. Ingredients include powdered sea kelp, French green clay, babassu oil, and essential oils. Technical information: 16 oz / 454 g / 1 lb batch — 6% superfat — 31.9% lye concentration. This recipe traces very quickly and does not require an immersion blender.
Author Lovely Greens
Cost 15


Lye solution

Solid oils

Liquid oils



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.
  • Use an ordinary kitchen knife to cut it into bars. Their thickness is up to you. The soap may be yellower than the cured soap after just being cut, and the seaweed pieces won't have had time to infuse a halo of color around them so don't worry if your bars don't look light green right away
  • 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.


Lastly, are you a beginner soapmaker looking for more guidance on how to make handmade soap? Enroll in the Natural Soapmaking for Beginners Online Course to get up to speed quickly. You’ll learn all about soap ingredients and equipment and be guided through step-by-step soap recipe videos. Learn more
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Recipe Rating


  1. Elizabeth says:

    Hi Tanya,
    Thank you so much for this website. I have just found it and subscribed to your newsletter.

    I am very excited to try this recipe. Can I increase the castor and olive oils in place of rice bran oil and substitute shay butter for mango butter? I wish to only use certified organic ingredients and I cannot get organic rice bran oil or mango butter. Thank you!

    1. Hi Elizabeth and welcome! You can change a soap recipe using the online SoapCalc but the lye amount will change, as well as the final qualities of the soap. Castor oil should only be used at around 5-8% of soap recipes, and more than that can lead to stickiness in the bars. Olive oil can replace the rice bran oil, though, and you can swap shea for mango.

  2. Matija McCarthy says:

    Hi my name is Matija McCarthy and I was wondering if you can make a seaweed gel soap recipe with Citric acid in it because I’m worried that some people who live in humid and hot areas with no air conditioning or dehumidifier will attempt to make your recipe but ultimately will end up with a bar soap filled with rancid bacteria like soap scum or DOS (Dreaded Orange Spots), is possible you can make this type of recipe and show it, please?

    1. Hi Matija, there is no worry of DOS in this recipe from using dried seaweed powder. In places that are humid and hot, the danger of DOS comes directly from the soap itself. Any cold-process bar soap with a superfat can turn rancid from the natural glycerin in the bars attracting moisture to the soap. That extra moisture/condensation causes the superfat oils to go rancid. Even in the case of soap with no soap additives, botanicals, scent, etc.

  3. Jacinta Negri says:

    Hi Tanya,
    Am really living exploring your recipes. I made this recipe 2 days ago and have found that the soap is really soft. I’m worried that it might no garden. What could be causing this given all the measurements were correct? Many Thanks, Jacinta

    1. Hi Jacinta, soap can be quite soft at first and needs the four-to-six week curing process to harden up completely :)

  4. Mary McAndrew says:

    Hi Tanya!
    I’m excited to try this recipe or any of the recipes you have shared. I’m buying different ingredients to start, I have a bunch as I like making lotion bars. This one has two oils I don’t have, rice bran and babassu, I’m guessing you need to stick to these for the recipe? Lucky I do have some dried bladderwrack, saved from when I lived in Northumberland. I like your idea of infusing it first in the water, if I use 1 part bladderwrack to 3 parts water, then do I just blend that all together and use for my water?
    Thank you and HUGE congratulations to you on the UNESCO award!!! You’re a great role model to everyone!

    1. Thank you so much, Mary! :) As for your questions — you can use seaweed in any soap recipe, really. Use one of my others, like the eco-friendly soap recipe, and add the seaweed in the same way/quantities as in this one. Bladderwrack — you’ll need a bit more water to reconstitute it (make it soft again) so one part seaweed to four parts water might be better. Based on the amount of water needed for the soap recipe, of course. Good luck, and have fun!

  5. Christina says:

    Hello! It would be really great if you could publish the recipe.
    Every recipe of yours I’ve tried is just amazing.

    Thanks so much!

  6. Hi Tanya,
    First I love your website it’s full out wonderful ideas and everyday helpful hints. I just read your article on “Rosemary, Kelp & Tea Tree Oil Soap “. I never knew that Bladderwrack & Sea Kelp had such wonderful qualities. My question is will you be sharing that soap recipe with your readers?
    Another comment is, I love that your soap recipes make smaller batches. Most of the recipes I find make huge amounts which take so long to use up. I prefer the smaller batch so I can experiment with more different recipes.
    Thank you again for your wonderful webpage.

    1. Hi Kit, this is one of my truly ancient blog posts that I’ve yet to update. I plan to very soon though and with a small batch recipe too :)

    2. The Recipe doesn’t seem to be loaded . I’d love to try it

  7. connie davis says:

    Hi Tanya, would you be so generous to share the amounts of rosemary, ginger & tea tree essential oils/weight of base oils for this soap?? It sounds so wonderful…thanks for your help!!

      1. Thank you for any help!

  8. Hi Pat – I think your story is acted out at least once by everyone who grows Calendula – me included :) I understand that hoverflies love them, and they love eating green fly as well. But maybe it's just that the calendula grow so big that the beasties just don't see the veg! haha

  9. Hi Jo – thank you and I'm glad you're interested in all the ingredients! I'm fascinated with the variety of wonderful oils, essential oils and botanicals available for soap making. It makes it such a creative craft.

  10. Hi Sunnybrook – It sounds like you had a bit of a mishap with your first batch of soap but that's great that you want to give it another go! There are LOADS of recipes and instructions online but often the information is structured for someone who understands the basics of soap-making. It can be really confusing at first so I'd recommend that you invest in a good beginner's soap making book to use as a reference.

  11. Sounds wonderful Tanya. I do agree about calendula. I made the mistake this year of sowing mine too near to the row of Swiss chard. The poor old chard got almost swamped and I know already that I shall not have to sow any calendula next year – it will be all over the garden. But it does help to keep the green fly away I am told.

  12. Do you recommend some simple directions for making soap that I could look at on the internet? I tried once and I think I made weed killer instead of soap, duh.
    My great grandmother used to save her grease from cooking and make unscented soap that they used for laundry and about everything back then.

  13. The soap looks so pretty. I was interested to read about the ingredients.

  14. I love making soap…it's so addictive! And tell me about it with the difference in oven temps. I had no clue when I first started using a fan assisted oven – I'll bet you can imagine how dry some of my cakes were ;)

  15. Oooh! That does sound good! I've not had time to play with soaps since my first foray :(
    I'm so pleased you mentioned fan ovens, usually i have to recalculate as I have found they differ from conventional ovens quite drastically sometimes ;)