Thuja is a general term for trees of the genus Thuja, which belongs to the Cupressaceae or cypress family.

The most common species in North America are Thuja occidentalis, whose common names include arbor vitae or tree of life, white cedar, yellow cedar, American cedar, hackmatack, Thuia du Canada, swamp cedar, and Lebensbaum; and Thuja plicata, the Western red cedar. The species of cedar found in China and Japan is Thuja orientalis, and is known as ce bai ye or ya bai shu in Chinese.

Thujas are evergreen conifers, or cone-bearing trees. The name “Thuja” was given to this group of trees by the Swedish botanist Linnaeus in 1753; it comes from the Greek word thuo, which means “to sacrifice,” as cedar wood was often burned with animal sacrifices by the ancients to add a pleasing aroma to the fire.

Thuja occidentalis is native to North America and grows in dense forests in southeastern Canada and the northeastern United States. American cedar trees grow to a height of about 60 ft (18.2 m), with trunks between 12 and 24 in (31 and 61 cm) in diameter. They are slow-growing trees, and prefer wet soils.

American cedars are some of the oldest trees in northern woods; some are estimated to be at least 800 years old. Thuja occidentalis is conical in shape, with the lower branches almost horizontal to the ground and the upper branches more nearly vertical, forming a dense cone at the top of the tree.

The leaves of the American cedar are bright green, opposite leaves that resemble overlapping scales, and give off a fragrant odor when crushed. The tiny yellow or greenish flowers appear between April and July. American cedar cones are pale green when young but turn a pale reddish-brown color as they mature.

The Western red cedar, or Thuja plicata, which is found from Alaska southward to the Pacific Northwest, Montana and Idaho, Alberta, and British Columbia, is similar in shape to Thuja occidentalis, except that it is a much taller tree, growing to a height of 150–200 ft (46–61 m).

Thuja orientalis, on the other hand, is a short tree growing to a height of only 12–20 ft (4–6 m), and is sometimes used to form hedges, as it tolerates pruning. The Chinese cedar, however, is not as hardy as its North American counterparts.

Thuja is also the name for a homeopathic remedy made from Thuja occidentalis.

General use

Thuja occidentalis as green fences
Thuja occidentalis as green fences

Cedar trees in general have a long history of use for furniture and buildings as well as in various herbal remedies and aromatherapy preparations. According to the Old Testament, King Hiram of Tyre sent cedar wood from Lebanon to King Solomon for the construction of the Temple in Jerusalem.

Cedar wood has also been used for centuries to line closets or make chests to protect clothing from moths. The fragrant wood was also used by Native Americans as well as the ancient Egyptians, Greeks, and Romans as an ingredient in incense blends.

In Western herbal medicine, cedar leaf oil was used as an emmenagogue, abortifacient, vermifuge, diuretic, and digestive aid.

It was applied externally to relieve the pains of arthritis and rheumatism, to treat external fungal infections of the skin (ringworm and thrush), and to remove anal or genital warts. Native Americans used cedar leaf preparations to relieve headache and to prevent scurvy.

Cedar leaves and twigs are in fact rich in vitamin C, and it was their effectiveness in preventing or treating scurvy that led to the tree’s being called arbor vitae or tree of life. In addition, recent research has shown that extracts prepared from either Thuja occidentalis or Thuja plicata do in fact have antiviral, anti-inflammatory, and antibacterial properties.

A group of German researchers reported in 2002 that an extract prepared from cedar leaf, alcohol, and water inhibits the reproduction of influenza virus type A, while a team of researchers in Japan found that an extract of Western red cedar was effective in treating eczema. Lastly, another group of Japanese researchers reported in 2003 that several compounds isolated from the stem bark of Japanese cedar appear to have significant antitumor activity.

In traditional Chinese medicine, the leaves and stems of Thuja orientalis are used to treat nervous disorders, insomnia, and heart palpitations, as well as to stop hemorrhages and bring down fevers.

Traditional Chinese physicians also make a preparation of fresh cedar leaves steeped for seven days in a 60% alcohol solution to promote hair growth. The mixture is rubbed on the bald spots three times daily.

The homeopathic preparation known as Thuja is made from the leaves of Thuja occidentalis, and is given to treat soft or bleeding warts on the chin, genitals, or anus.

The most widely used homeopathic materia medica, or reference book, also recommends Thuja for headaches that feel like a nail is being driven into the head; vertigo brought on by standing up; emotional depression and restlessness; pain or itching in the scalp; painful swallowing or a feeling of obstruction in the throat; intense thirst at night or early in the morning; stomach cramps that are worse in the evening; difficulty in breathing combined with a violent thirst for cold water; frequent need to urinate, with frothy or cloudy urine; insomnia or restless sleep; or fever and chills that grow worse toward evening.

Thuja leaves
Thuja leaves

In aromatherapy, cedar leaf oil is classified as a base note, which means that it has a very long-lasting scent when added to a perfume or incense blend.

One Canadian producer of essential oil advises, “… the scent is strong and should be used sparingly. One small application is all you need!” It is considered to have a sedative or calming effect, and is recommended for treating anxiety states as well as asthma, bronchitis, and head colds. Some aromatherapists also recommend cedar leaf oil for treating acne and dandruff.

Cedar leaf oil is still used in some mainstream over-the-counter (OTC) preparations to relieve congestion in the upper respiratory tract. The best-known of these cold remedies is Vicks VapoRub™, which can be applied directly to the chest and covered with a hot towel, or added to a vaporizer to produce fragrant steam.

Cedar leaf oil is also added to pest repellant sprays and paints to protect against mites, moths, and rodents. It is used to scent some brands of shoe polish, and is blended into some men’s colognes, including Hugo Boss and Ralph Lauren’s Safari.


Most products used in Western medicine and aromatherapy that contain cedar oil are made with oil from the leaves and twigs of Thuja occidentalis.

These parts of the tree yield about 1% volatile oil, which is about 65% thujone. The other components include fenchone, borneol, limonene, pinene, camphor, myrcene, a flavonoid known as thujin, and tannin. The essential oil is either clear or pale yellow in color.

Most of the cedar leaf oil used in North America is made in Quebec by small family businesses; about 80% of their production is sold in the United States. The oil is extracted from the leaves by a process of steam distillation, cooled in an indirect contact heat exchanger, filtered, and stored in barrels for distribution to wholesalers.

According to a Canadian producer, essential oil from American cedar can be applied directly to picnic tables or outdoor furniture as a natural insect repellant, or to wooden drawers or closets to repel moths.

A few drops of cedar leaf oil can also be added to a pail of warm water for damp-mopping hardwood floors. When the oil is used in aromatherapy, a few drops are mixed with several ounces of safflower or another vegetable oil for massages, or added to bath water for hydrotherapy.

Essential cedar leaf oil should never be applied directly to the skin, as it can cause irritation. It should be mixed with softened beeswax or a mild cream if used externally to treat aching muscles or joints. A 1/2-oz bottle of the oil costs about $10 in health food stores.

For internal use as a diuretic or expectorant,Western herbalists recommend taking 1/4-tsp of liquid extract of cedar leaf in a glass of water three to six times a day. Alternately, an infusion can be prepared by adding 1 ounce of fresh cedar leaves to a pint of boiling water. The infusion is taken cold in 1-tbsp doses every three to six hours.

Homeopathic preparations of Thuja include pills, granules, and liquid dilutions, in potencies ranging from 3X to 50M. The cost of these preparations ranges from $5.99 for a half-ounce container of 3X pills to $43.69 for a 1-oz (28-g) bottle of 50M liquid dilution.

Tinctures of Thuja are sold only to homeopathic practitioners, and cost around $8 for a 1-oz bottle. Boiron, a well-known manufacturer of homeopathic remedies, also offers a Thuja ointment for the treatment of external warts; a 1-oz (28-g) tube costs between $5.05 and $7.24, depending on the supplier.

Incense made from pure cedar or containing a mixture of cedar and other fragrances is available in stick or cone form for prices ranging between $1.49 and $5 for two to four ounces of incense.


Thuja with cones
Thuja with cones

Herbal preparations for internal use that contain cedar leaf oil should not be used by pregnant women, as the oil may cause contractions of the uterus.

In addition, anyone using the essential oil for external applications is advised to consult either a professional aromatherapist or their physician beforehand, as the high content of thujone in cedar leaf oil is a health concern. Thujone in pure form is a neurotoxin, which means that it affects the central nervous system in humans and other mammals.

Absinthe, a liqueur containing thujone derived from wormwood, can cause convulsions, hallucinations, and psychotic episodes. Absinthe has been banned in the United States, as have flavoring agents containing thujone.

In addition to products containing thujone derived from wormwood, products made with cedar leaf oil have been investigated by the U. S. National Toxicology Program to make certain that workers involved in the manufacture of perfumes or other products scented with the oil were not at risk.

The agency reported that the oil does not appear to be harmful to the skin or respiratory system under ordinary workplace conditions; all known instances of thujone poisoning since 1968 have been caused by drinking absinthe or undiluted essential oils of wormwood, sage, or cedar. With one exception, all these poisonings took place in France.

Side effects

No side effects have been reported as of 2004 from the use of perfumes, incense, aromatherapy products, pest repellants, or OTCs for external use that contain cedar leaf oil when used as directed. In addition, no side effects have been reported for homeopathic preparations containing Thuja.


No interactions between products containing cedar oil and prescription medications have been reported as of early 2004.