Infusing Oil with Herbs for Soap

What an infused oil is and why use it in soap

An herbal infused oil, sometimes called a macerated oil, is a carrier oil that has had plant material steeped in it for a period of time. The oil picks up some color, scent and fat-soluble plant compounds from the herb. The plant material is then strained out, leaving a flavored oil you can use in skincare, balms, salves and soap.

For soap, infusing is popular because it carries an herb’s character into the bar without leaving brown flecks, and without putting the herb through the lye solution directly. It is also one of the easiest ways to start working with the herbs described in our herbs for soap making guide.

What you need

A clean, dry glass jar with a tight lid
Dried herb or flowers
A carrier oil you plan to use in your soap recipe
A spoon or chopstick, kept completely dry
Muslin, cheesecloth, or a fine strainer
A clean, dry storage bottle or jar, ideally dark glass
A label and marker

Choosing herbs and oils (what herbs can go in soap)

Herbs often used for infusing include calendula, chamomile, lavender, rosemary, peppermint, plantain and comfrey. Choose herbs from a reputable supplier that are labeled for culinary or cosmetic use, and check each one for any allergy or sensitivity concern before using it on skin.

For the oil, pick one that is already in your soap recipe, such as olive, sunflower, sweet almond or coconut oil. That way the infused oil can replace the same oil in the recipe without changing the formula. Note that sweet almond and other nut-derived oils may be a concern for anyone with nut allergies, so label products that contain them.

Cold (room-temperature) infusion

Make sure the jar is clean and completely dry.
Fill the jar loosely with dried herb. Do not pack it so tightly that the oil cannot move through it.
Pour the oil over the herb until it is fully covered, with a little extra oil above the plant material. Herbs left exposed above the oil can invite mold.
Stir gently with a dry utensil to release air bubbles.
Close the lid, label the jar with the herb, oil and date, and store it away from direct strong sun. Some makers prefer a sunny windowsill; others prefer a warm, dim cupboard. Both approaches are used.
Shake or swirl the jar from time to time.
Strain after the infusion time (see below), pressing the herb to recover the oil.

Gentle heat infusion

If you do not want to wait weeks, use low heat.

Place the herb and oil in a heat-safe jar or bowl set over barely simmering water, or in a slow cooker on its lowest setting.
Keep the temperature low and gentle. The goal is to warm the oil, not to fry the herb.
Heat for a couple of hours, checking regularly. Many instructions suggest roughly 2 to 6 hours, depending on the herb and the heat source.
Let the oil cool, then strain.

Many makers feel heat-infused oils are a little less rich than slow infusions, but they are useful when you need the oil sooner.

How long to infuse herbal oil

Timings vary by source and method. As a general guide:

Cold or sun infusion: commonly around 4 to 6 weeks, sometimes longer.
Gentle heat infusion: a few hours.

Longer is not always better. If the oil starts to smell off, look cloudy in an unusual way, or shows any fuzz or bubbles, discard it.

Straining, storing and labeling

Strain through muslin or a fine strainer, then let the oil settle for a bit before bottling.
Store in a clean, dry container in a cool, dark place.
Label with the herb, oil and date made.
Infused oils generally keep for a limited time, often cited as up to about a year when stored well, but it depends on the carrier oil. Some oils turn rancid faster than others, so use older oils first and trust your nose.
If you will not use it soon, make small batches.

Avoiding botulism, mold and spoilage

Botulism concerns come up with herb-in-oil preparations because Clostridium botulinum can grow in low-oxygen, low-acid, moist conditions, which is a known concern for fresh garlic or herbs stored in oil for food. Infused oils made for soap or skin are not meant to be eaten, but moisture is still the key problem: it invites mold and bacteria and can spoil the oil.

To lower the risk:

Use dried herbs. Fresh plant material contains water, and many guides recommend dried herbs for longer shelf life. If you grow your own, dry them fully first.
Keep everything dry. Use dry jars and utensils, and do not wash the herb.
Keep the herb submerged, and avoid large air gaps.
Discard if in doubt. Mold, a sour or musty smell, or visible water droplets are all reasons to throw the batch away.
Do not eat infused oils intended for soap or cosmetics. If you want to make infused oil for food, follow current food safety guidance from a trusted source, as food use has stricter requirements.

Using the infused oil in soap

Treat the infused oil like any other oil in your recipe. Enter it in a lye calculator along with the other oils so you get the right lye amount. A common approach is to replace some or all of one of your liquid oils with the infused version.

If you are making a first batch, replace only part of the oils so you can see how it behaves. Some makers worry that an herb’s qualities will not survive the lye, and there are different views on how much of an infusion’s benefit remains in a finished bar. Sensible expectations are a gentle color or scent and a handmade feel, not a medicinal effect. Infused oils can also go into the oil phase of a homemade lotion, which needs its own preservative and safety steps.

For a calendula example, see our infused calendula oil recipe.

Which herbal soap is best for skin?

It depends on your skin. Mild infusions such as calendula or chamomile in a simple, gentle soap base are popular for people who prefer lower-fragrance bars. Strongly scented herbs and essential oils can bother some skin, so start simple and patch test finished soap.

Troubleshooting

Oil smells weak: try a longer infusion, or use more herb in the next batch.
Oil is cloudy: let it settle and decant, or filter again. Persistent cloudiness along with off smells can mean moisture, so discard it.
Oil went rancid: use fresher oil next time, store it cooler and darker, and make smaller batches.
Color is faint in the finished soap: infused oils usually impart subtle color, so do not expect bold results.