There are two main ways to make infused herbal oils. One way is to simply infuse a carrier oil such as olive or almond oil with a certain amount of essential oils. This is about as easy as it gets but there are a few caveats.
Topical oil infused with essential oils
Essential oils need to be treated with great respect because they can often be caustic to tissues when applied directly. That is why it is generally key to dilute essential oils in a “carrier oil” or soap. Carrier oils have different properties and choosing a good one depends on a person’s needs.
Diluting essential oils so they are not caustic is key to the safe practice of aromatherapy. Generally most essential oils should be diluted to about 2-3 % when added to a carrier oil. To achieve 2 % concentration, you would add about 15 drops of essential oil to an ounce of carrier oil. To understand more about safety and gain more education please check out the National Association for aHolistic Aromatherapy.
So for example, one could make a nice uplifting oil with one ounce of almond oil and then adding 9 drops of lavender, 3 drops of bergamot and 3 drops of sandalwood. Check out the aromatherapy sections under recipes to get some good ideas of blends.
Topical oil infused with fresh or dried herbs
There area number of herbalists that I know that are just not fond of essential oils. They think that they are too strong and too potentially caustic, and that it is better to work with the plants themselves to make infused oils. Many herbalists who follow Susun Weed and Wise Woman Ways prefer working with whole plants in this way. Infusing fresh or dried herbs into oils take a little more work but can really pay off in a number of ways. When working with whole plants, you have a more direct relationship with the herb, especially if you yourself gather it in the field. It can feel quite powerful to gather fresh mullein flowers from a beautiful nearby field and then infuse them in oil and use it as medicine later down the road.
So in general most herbs you infuse in oil should be dried, but there are a few exceptions: garlic, mullein flowers, arnica and St. John’s Wort comes to mind.
Some of the best ones to infuse as dried plants include burdock, calendula, cayenne, comfrey, devil’s club, elder, ginger, marshmallow root, mullein leaf, nettle leaf, plantain and yarrow. (Shout out to James Green for that nice list. Please buy his book The Herbal Medicine-Makers Handbook.)
To infuse an oil with herbs, simply loosely pack herbs in a jar and then fill the jar up with oil to the top with enough room to cover the herbs. (herbs exposed to fresh air can mold). Then place the container in a warm dark corner for 2 weeks. Then strain out the herb and voila, you have a nice infused oil. I’m not going into making a quicker infused oil via hot extraction but you can find out how here:
How to make a Heat-infused Herbal Oil by The practical Herbalist