Benefits, Dosage, Side Effects, and More
Oak bark (Quercus alba) comes from trees of the Fagaceae family, typically white oak varieties native to North America.
It’s derived from the inner bark and round growths known as galls that form on the tree.
Oak bark can be dried and ground into a powder for topical and oral use, and it has been used for medicinal purposes throughout history(1).
Topical applications are thought to suppress inflammation and soothe itchy skin, while oak bark tea is used to help treat diarrhea, the common cold, sore throats, bronchitis, loss of appetite, and arthritis.
A variety of naturally occurring compounds in oak bark, especially tannins, are thought to be responsible for its claimed medicinal properties (2).
Interestingly, the high tannin content of certain wines is typically a result of aging wine in oak barrels (3).
Oak bark is sold as a powder, tea, pill, and liquid extract. It’s available over the counter in the United States and may be labeled as white oak or different varieties of its genus Quercus, including robur, cortex sessilifora, and pedunculata (4).
Oak bark’s main uses relate to treating inflammatory conditions, such as bleeding gums and hemorrhoids. It’s also used to treat acute diarrhea.
However, there’s very little research to back its proposed benefits.
Oak bark may contain up to 20% tannins depending on the type and time of harvesting (5).
Tannins act as astringents, or agents that bind to proteins in the skin to constrict body tissues, therefore tightening pores and drying out irritated areas (6).
In particular, the tannins in oak bark have been shown to inhibit the release of inflammatory compounds. They may also exhibit antibacterial properties by binding with proteins involved in bacterial growth (5, 7).
These specific properties of tannins are responsible for the possible topical uses of oak bark in treating skin irritation and wounds.
Hemorrhoids, or swollen veins around the anal area, are sometimes treated by bathing in water mixed with oak bark powder to dry out sores (8).
Oak bark is also used for its astringent and antibacterial properties for wounds, irritated gums and teeth, and burns at risk of infection. It may be gargled, drunk, or applied topically (9).
One test-tube study found that an ointment consisting of oak bark and other extracts was effective against drug-resistant bacteria, including Staphylococcus aureus (10).
However, it cannot be determined whether oak bark or one of the other extracts was responsible for these antibacterial effects.
Thus, more extensive research is needed to understand the safety and effectiveness of oak bark.
While the use of oak bark in soothing skin irritation may be widespread, research on its use for this purpose is scarce. In some instances, oak bark may even aggravate irritation, especially when used on broken skin (8).
In addition to its topical applications, oak bark is thought to provide healing benefits when ingested.
Oak bark tea, in particular, is used to help treat diarrhea because of its antibacterial properties (5).
Test-tube studies suggest that oak bark may help fight bacteria that can lead to stomach upset and loose stools, including E.coli. Tannin compounds may also strengthen the intestinal lining and prevent watery stools (11, 12).
Furthermore, research in humans supports the use of tannins to treat diarrhea.
One study in 60 children with acute diarrhea found that those who received a supplement with tannins along with a rehydration regimen had significantly fewer stools after 24 hours, compared with their baseline (13).
However, there was not a significant difference in the median duration of diarrhea after treatment between those who received the supplement and rehydration, compared with those who just received rehydration (13).
While these results are interesting, no studies have specifically focused on the compounds in oak bark.
Thus, it’s unclear if the long-term use of oak bark tea and other products is safe and effective at treating diarrhea.
Some of the compounds in oak bark, such as ellagitannins and roburins, may act as antioxidants. Antioxidants protect your body from underlying damage caused by reactive molecules called free radicals (2).
The antioxidant activity of these compounds is thought to boost heart and liver health and possibly offer anticancer effects (2).
One study on ellagitannins from oak bark found that rats who received oak bark extract for 12 weeks while eating a high fat, high carb diet experienced improvements in heart and liver function, compared with rats who did not get the extract (14).
Another study in 75 adults with temporary liver failure found that those who took oak wood extract for 12 weeks had significantly better improvements in markers of liver function, compared with those who did not take the supplement (15).
However, the availability of ellagitannins and their byproducts in the body varies by individual. Thus, oak bark may not provide the same benefits for everyone (16).
More extensive research is needed to understand the safety of the long-term use of oak bark products.
To date, there’s not enough research to identify all possible side effects of oak bark tea, supplements, and lotions.
Oak bark is generally considered safe when taken for short periods, specifically 3–4 days for the treatment of acute diarrhea and 2–3 weeks when applied directly to the skin (17).
Personal accounts suggest that oral forms of oak bark may cause stomach upset and diarrhea. Meanwhile, topical oak bark applications may lead to skin irritation or worsen conditions like eczema, especially when used on broken or damaged skin (18).
Additionally, high doses and/or the long-term use of oak bark may worsen kidney and liver function.
One study in rats found that doses of 15 mg of oak bark extract per pound (33 mg per kg) of body weight led to kidney damage (19).
Due to a lack of research on the use of oak bark in humans, there’s no recommended dosage.
Instructions provided on oak bark pills, tinctures, teas, and lotions vary widely.
For better absorption, some instructions suggest not taking oak bark supplements or teas with food.
According to the European Medicines Agency, the following are the generally recommended dosages of oak bark for different purposes — both for internal and external use (17).
- Oral supplements: up to 3 grams per day
- Teas (for diarrhea): 1 cup (250 mL) of oak bark tea up to 3 times per day, or the equivalent of 3 grams per day
- Duration: 3–4 days
- Baths (for hemorrhoids or skin irritations): 5 grams of oak bark boiled in 4 cups (1 liter) of water before adding it to a bath
- Skin rinses or gargles (for skin irritations or sore throats): 20 grams of oak bark boiled in 4 cups (1 liter) of water
- Duration: 2–3 weeks
How to make oak bark tea
Oak bark tea is available in loose leaf or tea bag form.
To make it, steep a tea bag in 1 cup (250 mL) of hot water. You can also boil up to 3 grams (3/4 teaspoon) of dried oak bark in a few cups of water, strain, and drink.
There are no known reports of oak bark overdose.
Still, it’s important to adhere to the directions on the label. Since there are concerns about the long-term use of oak bark, be sure to check with a healthcare provider before taking it.
There have been no reports of oak bark interacting with other drugs or supplements.
However, it’s best not to take oak bark with iron supplements, as tannins may interfere with iron absorption (17).
Oak bark tea, supplements, and lotions should be kept at room temperature in a cool, dry place. The shelf life of these products varies and should be listed on the label.
There’s not enough information on the safety of oak bark preparations among pregnant and breastfeeding women.
Thus, oak bark should not be used by these populations (17).
Oak bark is generally safe when used in recommended amounts for short durations, but its safety in specific populations remains largely unknown.
There are concerns that oak bark is unsafe for individuals with impaired kidney or liver function. As such, it should be avoided in these groups (17).
Due to a lack of research about its effects, children, older adults, and people with underlying health conditions should not use oak bark unless a healthcare provider instructs them to do so (17).
The short-term use of oak bark tea may help with acute diarrhea, but so can other foods that do not have unknown side effects.
For example, eating foods like bananas, applesauce, white rice, or toast can improve acute diarrhea. Over-the-counter drugs, such as loperamide, are also effective.
All-natural alternatives for the topical use of oak bark include witch hazel, cucumber, apple cider vinegar, and rose water. These items contain similar astringent properties, but they should also be used with caution.