What is Bog myrtle / sweet gale?

Bog myrtle is a low, woody shrub of wet moors and peat bogs in northern Europe. Its leaves and catkins smell of resin and spice when you crush them. People used it to flavour beer, to scent linen, and to keep biting insects off the skin.

Its botanical name is Myrica gale. In Norway and Sweden it is called pors, and in Finland porssi. Today you may meet it as dried leaf tea, as sprigs for brewing, as a strong-smelling oil taken from the leaves, or inside an insect repellent spray.

Here is the honest verdict on evidence. Human studies are very few and very small. The best-tested use is keeping midges away, and even there it works less well and for less time than standard repellents.

Tradition tells you that people valued this plant for centuries. It does not tell you the plant works, and it does not tell you the plant is safe. Bog myrtle carries one specific hazard in pregnancy, which the safety section sets out.

How does Bog myrtle / sweet gale work?

No one has shown how bog myrtle works inside the human body. The human studies needed to say that have not been done.

The leaves hold a strong-smelling oil. In field tests on human skin, extracts of this oil kept biting midges away for a short while. The effect was real, but it faded faster than that of standard repellents.

In laboratory dishes, the oil slows the growth of some bacteria and fungi. It also kills some insect larvae in tests. Whether any of that helps a person with an infection is simply not known.

The leaves also hold chalcones called myrigalone A and B. In cell and plant studies these act as antioxidants and hold back the growth of other seedlings. Those are test-tube findings, not treatments.

One finding matters more than the rest. Germacrone, a compound in the leaf oil, has caused pregnancy loss in rodent studies.

Folk use of bog myrtle to bring on a late period fits that same picture. Treat it as a real risk, not a theory.

The bitter, tannin-rich taste is the likely reason it was brewed into beer and drunk after meals. Bitter plants can make the mouth water and may settle some people's stomachs. That is a general idea about bitters, not a tested fact about this plant.

What forms does Bog myrtle / sweet gale come in?

You are most likely to meet bog myrtle in these forms:

- Dried leaves, loose or in tea bags. - Fresh or dried sprigs sold to home brewers for gruit-style beer. - Spirits and bitters flavoured with the leaf, mainly in Nordic countries.

- The strong-smelling leaf oil, sold for use on skin or in scent blends. - Lotions, balms and sprays sold as midge or mosquito repellents. - Dried sachets placed with clothes to put off moths.

- Tinctures, which are leaf soaked in alcohol, though these are uncommon.

Strength is not controlled. A repellent lotion may hold only a trace of plant extract. The pure leaf oil is far stronger than anything you would drink.

Where it comes from:

Bog myrtle has a long, well-recorded place in northern European life. Before hops took over, brewers across Scandinavia, Britain and the Low Countries added it to ale in a herb blend called gruit.

Nordic households put sprigs among stored clothes and bedding to keep moths and fleas away. Walkers and farm workers rubbed the crushed leaves on skin against midges. It was also hung in rooms as a sweet, resinous scent.

Folk healers brewed the leaf as a bitter tea for a sour stomach and for worms. Washes of the leaf were applied to itchy skin and to scabies. None of this was tested in the way we test medicines now.

It also carried a darker use. The plant was taken by women to bring on a late period or to end a pregnancy. This page records that use as history and does not support it.

The plant is protected or locally scarce in some places. Picking from the wild may be restricted where you live.

What does Bog myrtle / sweet gale help with?

• Keeping midges and mosquitoes off the skin: This is the only use with real human testing behind it. Field studies in Scotland put bog myrtle extracts on volunteers' skin and counted midge landings. Fewer insects landed than on untreated skin. The catch is time. The effect faded within a couple of hours, well before standard repellents did. Think of it as modest and short-lived, not as protection you can lean on. Do not use it alone where insect-borne illness is a risk.
• Keeping moths away from stored clothes: Dried sprigs were a standard Nordic way to protect wool. The scent is strong and lasts for weeks in a closed drawer. Lab work shows the oil puts off and can kill some insects. Household testing against clothes moths is thin. It is cheap and low-risk for this use, but do not expect it to match a proper moth product.
• Flavouring beer, spirits and food: This use is well established and is the main one today. Brewers add the leaf for a bitter, resinous, slightly peppery note. Flavouring is a culinary use, not a health claim. Food amounts are small. Pregnant people should still avoid gruit ales and bog myrtle spirits.
• Upset stomach and poor appetite (traditional): Nordic folk practice used a bitter leaf tea after heavy meals. Bitter plants in general can stir appetite and saliva. There are no human trials of bog myrtle for digestion. The claim rests on taste and custom alone. If stomach trouble keeps coming back, get it looked at rather than treating it yourself.
• Itchy skin and scabies, as a wash (traditional): Leaf washes were applied to itchy skin, and in older records to scabies, which is caused by a mite. The oil does kill some small organisms in laboratory dishes. There is no human evidence that it clears scabies. Scabies needs proper treatment from a doctor or pharmacist, or it spreads through a household. The oil can also irritate broken skin.
• Intestinal worms (traditional): Bitter, resinous plants were widely given for worms in old northern practice, and bog myrtle was one of them. No human study supports this. Worms are easy to confirm and easy to treat with modern medicine. Self-treating with a strong herb is both unreliable and unnecessary.
• Bringing on a late period (traditional, and unsafe): This use is recorded in folk sources, and it is the reason the plant must be taken seriously. Germacrone from the leaf oil has caused pregnancy loss in rodent studies. Do not use bog myrtle for this. It cannot be dosed safely, it may harm you, and it may harm a pregnancy without ending it. If you need help with a late period or an unwanted pregnancy, see a doctor or a sexual health service.

Which foods are rich in Bog myrtle / sweet gale?

Bog myrtle is not a nutrient, so no food is rich in it. It appears as a flavouring in gruit-style ales, in some Nordic spirits and bitters, and rarely in game dishes. These are flavour uses, not sources of a health benefit.

What are the side effects of Bog myrtle / sweet gale?

• Itchy red rash where the oil or lotion touched skin
• Allergy, sometimes in people who react to other plants in the same family
• Stinging or burning on broken, raw or sunburnt skin
• Watering, stinging eyes if the oil gets near them
• Coughing or tight chest from breathing strong vapour
• Nausea or stomach ache from strong leaf tea
• Headache from the heavy scent

Good to know:

Most reports are mild and come from skin or scent contact. Serious harm from normal outside use is not common.

The pure leaf oil is the risky form. It is far stronger than tea and should never be swallowed.

The one serious concern is pregnancy, and it is covered in the safety section. Side effect reporting for this plant is patchy, so rare problems may simply be unrecorded.

How much Bog myrtle / sweet gale should you take?

• Recommended daily: There is no established dose for bog myrtle, and this page does not give one. No health authority has set a safe daily amount for the leaf, the tea or the oil. Strength also swings widely between plants and products, so an amount that fits one batch may not fit another. Two fixed points are worth knowing: - The leaf oil is not for swallowing, in any amount. - Flavouring amounts in food and beer are small, and are a culinary matter, not a dose. If a repellent product holds bog myrtle, follow the label on that product.
• Best time of day: Timing does not matter for health effects, since none are established. For repellent use, apply before you go out, and expect the effect to fade within about an hour or two. Midges are worst at dawn and dusk in still, damp weather. For moth sachets, time of day is irrelevant.
• With or without food: This does not apply in any tested way. Bitter teas are traditionally taken before or after meals, which is custom rather than evidence. A strong, tannin-rich tea on an empty stomach can feel harsh and may bring on nausea. The leaf oil is not taken by mouth, with food or without.
• Time to effect: As a skin repellent, the scent works at once and fades quickly. For any internal use, there is no honest answer. No trial has measured how long bog myrtle takes to do anything in a person. It may do nothing at all. That is a real possible outcome here, not a formality.
• How long to take it: No safe length of use has been worked out, because the studies do not exist. Long, daily use of the leaf tea has not been tested in people. Skin and repellent use is short-term by nature. Stop if your skin reacts. If you feel you need any herb day after day for a health problem, that problem deserves a proper look from a doctor.