Complete Guide to Natural Soap Additives

A comprehensive introduction to natural soap additives and why we add them to natural cold-process soap recipes. Includes natural soap colorants, fragrances, exfoliants, scent fixatives, and when to add citric acid and sugar to soap recipes.

In its purest form, natural soap requires just three ingredients: fat, lye, and water. Fats can be vegetable oils, butters, or waxes, and you have many options to choose from. You can also make soap with animal fat or waxes, such as lard, tallow, or beeswax. Natural soap recipes usually include three or more fats, combined with the right amount of lye and water to turn the fat into gentle soap. In most cases, any other natural soap additives in the recipe are optional.

I get a lot of questions about the cold-process soap recipes I share. Mainly, how to change a soap recipe, but they also ask whether they can leave an ingredient out. The simple answer is that the three main ingredient categories listed above are essential. You cannot omit one of them without impacting the whole recipe (and its safety for the skin). Any other natural soap additives listed in the recipe can be omitted, except for citric acid (see further below). These optional ingredients, called soap additives, add color, scent, decoration, and texture, and can improve or speed up processes.

Natural Soap Additives

Making handmade soap can be as straightforward or as complicated as you would like. It’s basically like everything else in life! Recipes and techniques can include exotic scents, intricate swirls, and all manner of expensive, and sometimes bizarre, ingredients. I wish more people would ask themselves, “Why am I putting this ingredient in soap?” rather than “Can I?”

The list of natural soap additives below describes what they are and why you would add them. Essentially, their purpose in a soap recipe and why they would be beneficial. Used in the right way and in the correct proportion, they can upgrade a simple soap recipe into something fabulous!

Yet, there’s a growing movement of people returning to the basics. Making pure, simple, unscented soap that gently cleans and doesn’t set off allergies. It’s food for thought when you’re using natural soap additives. My advice is to keep it simple and to use them wisely.

Essential Oils in Soap Recipes

Essential oils are concentrated and volatile plant chemicals extracted from leaves, flowers, fruit, and bark. They’re mainly extracted using steam distillation but can also be pressed or extracted using other methods. Essential oils are popular in complementary medicine, but in handmade soap, you mainly add them for scent.

The types suitable for soap and their usage rates vary, as explained in this piece. However, the most common essential oils for soapmaking are typically used at about 3% of the soap recipe by weight (excluding water). In some cases, the essential oil can also tint your soap.

Natural Soap Colorants

Without additives, handmade soap’s natural color tends to be off-white to creamy. To color soap, you need extra ingredients, most commonly powdered, that you add at trace or to the lye solution. You can also use natural colorants (both powdered and not) to infuse color into the lye solution or main soaping oils.

Cosmetic clays are probably the most common and stable natural soap colorants, and they come in an impressive range of colors. When using clay, use about one teaspoon per pound (454 g) of soapmaking oils. You can add it directly to the lye solution, or mix each teaspoon of clay with three teaspoons of distilled water, then add it to the soap batter at trace.

Botanicals for Coloring Soap

You can also use many of the same botanicals used in fiber dyeing to color your soap. They include alkanet, madder, annatto, indigo, woad, calendula, turmeric, coffee, and tea. Each botanical has a different usage rate and method, and this piece guides you on how to naturally color soap.

Bee propolis is another natural soap colorant; if you’ve ever seen a propolis tincture, you’ll know why! Other natural soap additives used as colorants include charcoal, cocoa powder, spices, natural oils, and plant roots, fruit, petals, and expressed oils. Aleppo soap, perhaps the oldest type of soap still made, is naturally colored green with laurel berry oil. You can also naturally tint soap using some fruit purees, including carrots and avocado.

Botanical Decorations on Soap

Sometimes, soap recipes call for dried leaves, fruit, fruit peel, seeds, or flower petals, but you don’t use them the same way as colorants. Instead, you use them to decorate the tops of soap bars and sometimes throughout the soap.

If you opt for these additives, use botanical decorations with a light touch. Some of the most beautiful decorations I’ve seen and used include a sprinkling of dried calendula flowers or cranberry seeds. It’s particularly effective to add texture to the tops of your bars with a spoon or skewer, then decorate them afterward with botanicals. When the soap has set and you’re ready to cut it, turn it upside down and cut from the bottom to the top. This stops the botanicals from dragging through your lovely handmade soap.

Decorating Soap with Botanicals

Though I love the look of botanically decorated soap, I wouldn’t recommend going overboard if you’re making soap for other people. Dried flower petals and soggy pieces of rehydrated orange slices can be unpleasant in the shower or bath. There’s also a concern that if they go down the drain, they can clog it.

For more information on using botanicals, read this piece on using herbs and flowers in soap recipes. It covers the types you can use and also some challenges (such as botanicals turning brown). Common botanical decorations include lavender buds, rose petals, cornflower petals, dried orange slices and peel, and coffee beans. You can also use more exotic ingredients, including moss and lichen.

Exfoliants in Soap Recipes

When we’re making scrubby hand soap or an otherwise exfoliating bar, we can use ingredients such as oatmeal, sea salt, luffa, coffee grounds, ground pumice, seeds, and shredded coconut. Some are more exfoliating (scratchy) than others, so again, use caution. Oatmeal is one of my favorite plant-based exfoliants, and colloidal oatmeal or even quick oats are gentler than whole rolled oats when mixing into oatmeal soap. Whole rolled oats make a good scrubby hand soap, though!

Poppy seeds are also a common exfoliant. Please be aware that the only poppy seeds you should use for skincare are the edible types from the breadseed poppy, Papaver somniferum. These are the types you’d use in baking, and the seeds are often massive. Big seeds can mean a scratchy bar of soap that some people find uncomfortable. Even though they look great, use restraint. The same goes for other seeds, such as cranberry seeds.

Another exfoliant that I use often is ground pumice. Pumice is a light volcanic rock, and you can find it in various grades, including extra-fine powder. It can clump together if you add it at trace, though, so I tend to add pumice to the melted oils and stick blend it in.

Using Silk in Soap

In my opinion, good natural soap already has a silky feel. However, some soapmakers (and sellers of soapmaking ingredients!) recommend using silk fibers and liquid silk in soap recipes. Both come from the cocoons silkworms create to metamorphose into moths and aren’t considered vegan or vegetarian. They collect the cocoons, kill the caterpillars, and use the fibers to make silk fabric and fiber.

To use it, dissolve the silk fiber in a hot lye solution or buy ready-made liquid silk and add it at trace. The natural keratin in silk adds a silky feel, and some people use snakeskin for the same purpose. Again, add it to the hot lye solution to dissolve, then strain out any pieces before adding the lye solution to the melted oils. As you can guess, snakeskin soap isn’t vegan or vegetarian either, though you’re only using shed skin rather than harming an animal.

Using Salt in Soap Recipes

There are two main reasons to add salt to soap: to create salt bars or to help the soap harden faster. In salt bars, you add salt at trace, and the final bars contain pieces of salt. They can be fine grains, large crystal salts, or a mix of both. Salt used this way creates a soap that is said to help with acne, exfoliate the skin, and offer other potential “detoxing” benefits. It can also last a long time even when wet in the shower.

To make salt bars, use 50-100% of the weight of your main soaping oils in a recipe. Salt affects how soap lathers, so recipes often use a lot of coconut oil to compensate. A high superfat of 20% is also calculated for the recipe so that the bars aren’t drying.

Salt Can Help Harden Soap

The second way to use salt in soap is to help speed up the soap hardening. It’s advantageous in recipes with a high amount of liquid oils, such as castile soap, since they often take a week or more to come out of the mold. To add salt to the recipe, use brine or seawater instead of water for the lye solution.

This soleseife recipe shows how to use seawater (3.5% salinity) to make soap. You can also make homemade brine using sea salt. All you do is dissolve sea salt or table salt in distilled water to make a concentration between 3.5-25% salinity. Then use it to make the lye solution.

Sodium lactate is another ingredient used for the same soap-hardening qualities. It’s the salt of lactic acid, a vegan ingredient derived from fermenting beets or corn.

Sugar and Honey in Soapmaking

There are a couple of reasons to use sugar in soapmaking – and by sugar, I mean cane sugar or honey. The first is color. Adding a small amount of either to the lye solution while it’s warm (under 150° F/65° C) caramelizes it, creating a soft caramel soap color and a sweet natural scent. If you want to try this out, use about 1/2 to 1 teaspoon per pound (454 g) of your main soapmaking oils. If you use too much, or if the lye solution is too hot, the sugar can scorch and make your soap smell burnt.

The other reason to use sugar in soapmaking is to boost lather. It helps in recipes low in coconut oil or that need a bit more fluffy lather. Adding honey or sugar to the lye solution can do this, but if you don’t want to affect your soap’s color, add sugar syrup to your soap batter.

Make sugar syrup by combining 1 cup sugar with 1/2 cup distilled water and gently heating it. Cool it, then use 1 teaspoon per pound of soapmaking oils, stirring it in at trace. Sugar can heat soap up, creating full or partial gel, so keep that in mind if you’re trying to achieve a light or consistent color.

Using Milk in Soap Recipes

Goat milk soap is one of the gentlest and most nourishing soaps you can make. Using goat milk instead of distilled water adds fats, vitamins, and lactic acid to your bars, making them more sensitive and creamy. Some even say that using goat milk in soap helps with eczema and psoriasis.

Milk also contains sugars, so when you use it to make the lye solution, freeze it beforehand or use this simple method. Otherwise, the soap may turn brown or smell unpleasant.

Though goat milk is the norm for milk soaps, you can also use other milks, including cow, camel, sheep, and even human breast milk. The latter is becoming popular in home soapmaking when mom has extra expressed milk to use. Creating a human breast milk soap for retail (legally) could be challenging in some places, but it’s perfectly fine for home use.

Fruit, Flowers, and Vegetables in Soapmaking

You can find fruit-based essential oils suitable for cold-process soap making, such as the gorgeous 10x orange and citrusy litsea cubeba. However, you can also use actual fruit, vegetables, and some plants in soapmaking. The benefits of using plants in soap vary: some fruit, flowers, and vegetables have no known benefits, while others, like carrots and pumpkin, can naturally color the soap. The gel inside aloe vera leaves is fantastic for making a gentle soap for both face and body. Cucumbers can do the same and could benefit those with inflamed skin.

In their whole form, fruit and vegetables will almost certainly rot in handmade soap, even if they’re dried pieces. Vegetable and fruit mass holds onto and absorbs excess water. They can also clash with soap’s pH and can start breaking down when exposed to air. The trick is to dry, juice, or puree them first.

Using Juice, Puree, and Powder in Soap

When it comes to juice or puree, you can replace some or all of the water in a soap recipe. For purees, a good amount to use in soap recipes is 1 oz (28 g) of puree per pound (454 g) of soapmaking oils, but you can use more if you wish. I use pumpkin puree in this pumpkin spice soap recipe.

With juice, you can easily use more; however, be aware that the natural sugars in some juices can scorch the lye solution if you use them. Instead, make a 1:1 lye solution and add 1 part juice to the melted soapmaking oils before you pour in the lye solution. For example, make a lye solution with 62 g distilled water and 62 g lye, then add another 62 g apple juice to the melted pan of oils.

If you dry and pulse the plant matter, you can add it as a fine powder either before or after trace, depending on the ingredient and technique. I tend to use 1-2 tsp of powder per pound of soapmaking oils. You can also use powders to make botanical teas, then use that cooled infusion to make the lye solution.

Another way to use botanicals in soapmaking is as decoration. If they’re small and dry enough, you can add them directly to soap for speckles of color, as with lemon and orange zest. You can also dry the plant material and use it to decorate the tops of soap. Imagine slices of dried orange or freeze-dried berries.

Citric Acid in Soap Recipes

There are two reasons to add citric acid to handmade soap: to reduce soap scum and prevent the soap from going rancid. In soapmaking, citric acid reacts with sodium hydroxide to form sodium citrate, a chelator that attracts metal ions. This means that if you wash with hard water or use tap water to make soap, citric acid will improve the bars’ lather and extend shelf life. It can also help prevent soap scum from forming. The metals and impurities in hard water and tap water cause oxidation to occur in your superfat.

Citric acid is also a useful natural soap additive in dish soap because it helps keep dishes sparkling clean and free of soap residue. I go through how to use citric acid in my dish soap recipe—it’s a really interesting process because citric acid consumes some of the lye used. It creates a lye discount, and you’ll need to compensate by adding extra lye to make up for what it uses.

Beer and Wine in Soapmaking

If you’d like to use a rich dark red wine to make red soap, forget it. Wine turns soap tan to brown, and if you don’t use it carefully, it can even make your bars smell a bit off. Although wine contains sugars that can boost lather, sugar or honey works much better (there are sections on both above). Though wine contains potentially health-benefiting compounds, it’s unlikely to affect your skin.

Beer, on the other hand, is an excellent natural soap additive! It adds a sweet, hoppy scent, a light brown color, and can even boost the lather. It may even help treat acne and eczema and soothe irritated skin.

A few things you need to know before making beer soap. First, boil beer first before using it in soapmaking. Alcohol can impede the saponification process and can sometimes end in a failed batch. The carbonation in beer and sparkling wine can also cause issues. Another issue is that beer and wine contain sugars, which can boost lather but can also heat the soap batter after you pour it into molds. Take precautions to keep the soap cool after you pour it into the mold(s), or you can get cracks and/or partial gels.

Scent Fixatives for Soap

If you’re using essential oil to scent soap, you will need a lot of it —I use generally about 3% by weight. Essential oil scent fades with time, especially if the soap is stored in a warm place. Though you might be tempted to use more than the recommended rates to counter this, you risk irritating the skin. Instead, soapmakers sometimes use fixatives to amplify and extend the scent life of essential oil soap. They include clay, orris root powder, benzoin resin, oatmeal, and even some essential oils.

With clay, you pour the essential oils into it the day before making soap. The idea is that clay absorbs it and slowly releases the scent even after it’s mixed into the soap. Oatmeal pieces in soap can absorb liquid and work the same way.

You can also anchor essential oils with other deep or long-lasting fragrances. That’s the case with musky, floral orris root powder, vanilla-scented benzoin resin, earthy frankincense gum, and woody yet pungent myrrh powder. There’s a lot of crossover between perfumery and soapmaking when it comes to making scent last!

Antioxidants in Soapmaking

If you’re making a good batch of handmade soap for the face or body, then it will have a superfat. An extra amount of oil that doesn’t turn into soap and stays in the bar, free-floating. The downside of using a generous superfat is that over time, the excess oil can go rancid.

Rancidification is the natural process of fatty acids reacting with oxygen and/or water and breaking down. It is characterized by yellow or brown spots on the soap and sometimes a strange, musty smell. Storing soap in sealed boxes does not work, as it only encourages the soap to sweat and go rancid anyway.

Using oils well within their best-by date helps prevent this from happening too quickly. Storing soap in the open but out of direct sunlight helps, as does avoiding oils that go rancid more quickly than others.

You can also add antioxidants such as grapefruit seed extract (GSE) and Rosemary oleoresin (ROE). These plant-based ingredients, in the right amount, can help prolong the life of fatty acids. Please note that they are not essential oils and that essential oils do not have shelf-life-extending properties.

Sometimes, you may see vitamin E in a soap recipe to prolong the soap’s shelf life as an antioxidant. It does not work, though. Vitamin E lacks the right type of tocopherol to extend the life of soap or other beauty recipes. In fact, according to Kevin Dunn, author of Scientific Soapmaking, it can do the opposite and make soap go off faster.

Ingredients for Skin Therapy

A whole category of herbal ingredients can be added to soap and may have skin-therapy properties. Neem oil or pine tar can help with eczema and psoriasis. Aloe vera and cucumber create a gentle bar. Some soapmakers also use herbs commonly used in skincare, including plantain, lavender, calendula, daisy, chamomile, and marshmallow root. They may be added as an infused oil, a tea, or a cold-water infusion.

I want to say that all of these ingredients benefit your skin in soap, but I’m not sure. Even if a compound survives saponification and the soap’s pH, is there enough of it to have an effect? If it can stick to your skin after you wash with soap, like superfatting oil, there’s potential. However, if it washes off after you use the soap, that skin therapy goes straight down the drain.

I’m a bigger advocate for using herbal extracts in balms, salves, lotions, and creams. Unless, of course, they offer another benefit, like calendula oil naturally coloring soap yellow. Infused oils as soap colorants excite me, and I’ve experimented with many different plants. In my eBook, Botanical Soapmaking: Oil Infusions for Vibrant, Natural Color, I share the most vivid soap colors you can create.

Unusual Ingredients in Soapmaking

Lastly, I’ve seen people use a whole list of unusual ingredients in soapmaking. Some are used in other beauty recipes, such as pearl powder for supposed skin lightening. Then there’s colloidal silver, amber resin, snail gel, cow bile, and kombucha. Even in health and skincare, there’s a lot of conjecture on what these ingredients can do.

Also, in some cases, using creative ingredients could be unethical, harmful, or detrimental to your soap batch. You might also be legally unable to sell soap made with certain additives in certain regions.

My advice: when it comes to unusual ingredients, research them first to make sure they aren’t harmful or react badly in cold process soap. Then ask yourself why you want to add it. What would the intended purpose be? Can science back up any claims you might want to make about soap made with an ingredient?

Soap Recipes Using Soap Additives

I hope that this list of natural soap additives has been helpful. Maybe even opened your eyes to new possibilities! But before you go wild with all these extras, remember what soap is and what it does. It’s the natural chemical result of combining fats, lye, and water and is meant to clean. Soap additives should improve its function, aesthetics, or experience.

If you’re new to cold process soapmaking, I cover the process in much more detail in the online soapmaking course. For natural plant-based colors, I recommend getting Botanical Soapmaking. Together, they’ll teach you about what ingredients are used in natural soapmaking, why they’re used, and how to make soap from start to finish. Here are a few free soap recipes that use different soap additives, too:

• Lavender Soap Recipe (with alkanet root)
• Natural Carrot Soap Recipe (with carrot puree)
• Gardeners’ Hand Soap (with poppy seeds)
• More Natural Soap Ingredients