D-limonene is a cyclic terpene of major importance with a strong citrus odor and bitter taste. D-limonene was primarily used in medicine, food and perfume until a couple of decades ago, when it became better known as the main active ingredient in citrus cleaner. It has very low toxicity, and humans are rarely ever allergic to it. Medicinally, Limonene is best known for treating gastric reflux and as an anti-fungal agent. It’s ability to permeate proteins makes it ideal for treating toenail fungus. Limonene is also useful in treating depression and anxiety. Limonene also assists in the absorption of other terpenoids and chemicals through the skin, mucous membranes and digestive tract. It’s also been shown to be effective anti-tumor while at the same time being an immuno-stimulant. Limonene is one of two major compounds formed from α-Pinene.