What is Hemlock spruce?
Hemlock spruce is the inner bark and resin of Tsuga canadensis, an evergreen tree of eastern North America. Folk and Eclectic healers used it as an astringent, a plant that tightens and dries tissue.
It is not poison hemlock. Poison hemlock (Conium maculatum) is a deadly weed in the carrot family. The two share only a name, and the mix-up has killed people.
The bark is very high in tannins, the same tart compounds that make strong tea pucker your mouth. Canada pitch is the sticky resin, once spread on cloth and laid on aching joints.
The honest verdict: human evidence is close to absent. Long traditional use is not proof that it works, and it is not proof that it is safe.
How does Hemlock spruce work?
The proposed action is astringent. Tannins bind to proteins on the surface of skin and mucous membranes. In test tubes this forms a tight, protective film.
That film is said to reduce weeping, oozing and loose stool. The idea is old and plausible. It has not been tested in people with hemlock spruce bark itself.
In laboratory tests, tannins and conifer oils slow the growth of some bacteria and fungi. Whether that happens on human skin or in the gut is not established.
The needle oil contains alpha-pinene and bornyl acetate. These smell sharp and clean, and they are the reason the oil is used in steam and rubs. Any warming feeling on skin comes from mild irritation, not from healing.
What forms does Hemlock spruce come in?
Hemlock spruce is a niche item. Most of what you can buy is dried bark or needle tea.
Forms you may see: - Dried shredded inner bark, for teas and skin washes - Liquid extract or tincture made from the bark - Needle tea, sold as a woodsy hot drink - Essential oil from the needles, for scent and steam only - Canada pitch, the resin, now rare
Buy only from sellers who print the Latin name, Tsuga canadensis. That is your main guard against a mix-up.
Never swallow the essential oil. Conifer oils can burn the gut and harm the lungs if they go down the wrong way.
Where it comes from:
Hemlock spruce bark was a staple of American folk medicine and of the Eclectic physicians of the 1800s. They were a group of US doctors who leaned on plant remedies.
King's American Dispensatory listed the bark as an astringent. It was given for loose bowels, used as a gargle, and used as a wash for sores.
Canada pitch plaster appeared in old US pharmacopoeias. The resin was warmed, spread on cloth and laid on the chest or a sore back.
The bark also had a large non-medical life. Tanneries stripped whole forests for it in the 1800s to cure leather. First Nations and settler households brewed the needles as a winter drink.
Who should avoid Hemlock spruce?
- Never confuse this with poison hemlock (Conium maculatum), a deadly weed; check the Latin name Tsuga canadensis on anything you buy
- Never swallow the needle essential oil, and never give it by mouth to a child
- Do not use the bark or its tea if you are pregnant or breastfeeding, as there is no safety data
- Do not give the bark tea to children, who are more easily harmed by tannins
- Do not take the bark tea if you have anaemia (low iron in the blood) or take iron tablets
- Avoid it if you have a peptic ulcer (a sore in the stomach lining) or ongoing reflux
- Do not take it if you have liver disease, since high-tannin products add to the liver's load
- Avoid it if you have had an allergic reaction to pine, spruce or fir
- Do not use steam or strong vapour near infants and toddlers
- Do not use it in place of care for diarrhoea with blood, black stools or high fever
When should you see a doctor?
Stop and get medical help the same day if a skin plaster leaves a burn, blister or spreading rash.
Go to an emergency department, or call poison control, if anyone swallows the essential oil. Watch for burning in the mouth or throat, vomiting, drowsiness, coughing or trouble breathing.
Treat any suspected poison hemlock mix-up as an emergency. Shaking, muscle weakness, a slow or racing pulse and breathing trouble need an ambulance at once.
See your doctor if diarrhoea lasts more than two days, or comes with blood, black stools, fever or dizziness.
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