Black alder (bark)

What is Black alder (bark)?

Black alder is the bark of Alnus glutinosa, a tree that grows in wet ground across northern Europe. Swedish names are klibbal and svartor. The Finnish name is tervaleppä.

In Nordic folk practice the dried bark was simmered in water. The liquid was used as a gargle, a wash for sores, or a drink for loose bowels. The bark is full of tannins, the dry, puckering compounds also found in strong tea and oak bark.

Watch the name. In North America "black alder" often means winterberry (Ilex verticillata), and some sellers confuse this bark with alder buckthorn (Frangula alnus), a strong laxative. These are different plants with different risks.

Here is the honest verdict. There are no good human trials of black alder bark for any health problem. Long traditional use is not proof that it works, and it is not proof that it is safe.

How does Black alder (bark) work?

The main idea behind the old uses is astringency. Tannins bind to proteins and make surface tissue feel tighter and drier. You can feel this in your mouth within seconds of a strong brew.

That effect is real as a sensation. Whether it speeds healing of a sore throat, a mouth ulcer or a bout of diarrhoea has not been tested in people.

Lab work on alder bark points to other actions. In test tubes, extracts mop up free radicals and slow the growth of some bacteria and fungi. In cell and animal studies, the compound oregonin appears to damp down markers of inflammation.

None of that has been shown to carry over to people. A test tube is not a throat, and an effect on cells in a dish often disappears in the body.

One traditional detail is worth knowing. Fresh alder bark can cause strong nausea and vomiting, so old handbooks called for bark dried and stored before use. The compound behind that effect has not been pinned down.

What forms does Black alder (bark) come in?

Black alder bark is not a mainstream product. You are most likely to meet it as loose dried bark from a specialist herb supplier.

Forms that turn up include:

- Cut or shredded dried bark, simmered into a decoction - Bark powder, sometimes in capsules - Alcohol tinctures from small herbal makers - Blends sold as mouth rinses or skin washes

Quality control is weak in this corner of the market. Mix-ups with alder buckthorn bark are the main worry, since that plant acts as a strong laxative. Buy only where the Latin name Alnus glutinosa is printed clearly.

Where it comes from:

Alder bark has a long record in Scandinavian and wider northern European folk medicine. Written notes go back to early modern herbals and continue through 19th century rural practice.

The bark was mainly boiled and used on the surface of the body. Reported uses were gargles for sore mouths and throats, washes for sores and swollen feet, and drinks for diarrhoea or fever.

Alder had a strong craft life too. The bark gave a brown or black dye for wool and leather, and tanners valued it for hides. Much of its reputation came from that dyeing and tanning power.

These are historical records of what people did. They are not a recommendation to repeat it.

What does Black alder (bark) help with?

• Sore throat and sore mouth, as a traditional gargle: This is the most common old use. Tannins give an immediate tight, dry feeling on inflamed tissue. No human trial has tested alder bark for throat or mouth pain. Any relief you feel may be the same soothing you would get from a warm salt gargle. Do not swallow large amounts of a strong brew.
• Short bouts of diarrhoea: Tannin-rich barks were a standard folk answer to loose bowels across Europe. The thinking was that they tighten the gut lining. There is no human evidence for alder bark here. Diarrhoea that lasts more than two days, or comes with fever or blood, needs a doctor rather than a herb. Fluids and salts matter far more.
• Minor sores and skin irritation, as a wash: Cooled bark decoction was used on scrapes, sores and weeping skin. In lab tests, alder extracts slow the growth of some bacteria and fungi. Whether that happens on skin is not established. Do not put it on deep wounds, burns or anything that looks infected.
• Bleeding gums and mouth inflammation: Astringent barks were used as mouth rinses in Nordic homes. The claim was that they firm up soft, bleeding gums. No trial supports this for alder. Bleeding gums usually mean gum disease, which responds to dental care, not a rinse.
• Fever, in older folk practice: Some old sources list alder bark as a fever remedy, probably by loose analogy with willow bark. Alder holds only trace salicin-type compounds. There is no evidence it lowers fever in people. Treat this one as folklore only.

What are the side effects of Black alder (bark)?

• Nausea
• Vomiting, especially with fresh or poorly dried bark
• Stomach cramps and queasiness
• Constipation after repeated use
• Lower iron absorption from food and supplements
• Dark staining of teeth or tongue from strong brews
• Allergic rash or itching, more likely if you react to birch or alder pollen

Good to know:

Most reported problems are stomach-related and settle once you stop. Nausea and vomiting are the classic ones, and fresh bark is the usual cause.

The bigger risk is not the plant itself. It is buying the wrong bark. Alder buckthorn bark looks similar and acts as a strong laxative, which can cause cramping, watery stools and salt loss.

Serious harm from correctly identified alder bark is not well documented. That partly reflects how little it has been studied.

How much Black alder (bark) should you take?

• Recommended daily: Black alder bark has no modern label standard, because it is not an approved herbal medicine anywhere. No safe or effective amount has been set in testing. Old European handbooks describe a decoction of roughly 2 to 3 grams of dried bark per cup of water. That is a record of past practice. It is not advice for you, and it has not been checked for safety. Fresh bark was always avoided in traditional practice because it causes vomiting. If you are thinking about using this herb, talk to a doctor or a trained herbalist first.
• Best time of day: Time of day does not matter for this herb. No study has compared morning with evening use. If you use it at all, keep it well away from iron tablets and other medicines you swallow. A gap of about two hours is the usual advice for tannin-rich teas.
• With or without food: Food helps. Tannin-rich brews on an empty stomach often cause nausea or a queasy, gripey feeling. The trade-off is that tannins bind iron and some drugs in food and tablets. So take it with or after a meal, but not with an iron supplement or a prescription dose.
• Time to effect: A gargle feels astringent at once, within seconds. That is a taste and texture effect, not proof of healing. For anything swallowed, there is no reliable timeline, because no human study exists. It may do nothing at all for your symptom.
• How long to take it: Traditional use was short and problem-led, measured in days rather than weeks. Tannin-rich barks were not taken as a daily tonic. Long use of strong tannin brews can upset the stomach and block iron uptake. No study has looked at what long use of this bark does. There is no safe long-term window to quote.