Sweating seems simple enough. We get hot, we sweat, and as that moisture evaporates from the skin it helps dissipate heat. In traditional herbal medicine, however, perspiration is viewed as part of a much larger physiological pattern. Herbalists have historically worked with a category of plants known as diaphoretics, particularly during the early stages of acute respiratory illness and fever. Elderflower, yarrow, peppermint, ginger, boneset, catnip, and several other familiar herbs have all found their way into traditional fever and cold formulas.
Diaphoretics are sometimes described as herbs that “make you sweat” or “break a fever.” While that makes the action easy to remember, it does not explain very much about what is happening. To understand why herbalist reach for these plants, it helps to understand what a fever is, why someone can be shivering while their temperature is rising, what happens when a fever begins to resolve, and why different diaphoretic herbs were chosen for very different presentations.
What Is a Diaphoretic?
A diaphoretic is an herbal action traditionally associated with promoting or supporting perspiration. The word comes from the Greek diaphorein, meaning to carry through or disperse. Older herbal traditions frequently used diaphoretic plants during febrile illnesses, particularly when someone was chilled, tense, restless, congested, or when the skin seemed hot and dry.
The important point is that diaphoretics are not interchangeable energetically. Some are warming and stimulating, while others are cooling or relaxing. Some are strongly aromatic and dispersive, and others appear better suited to patterns involving tension or constriction at the periphery. Memorizing that "diaphoretic equals sweating” leaves energetics completely out of the picture and relegates herbs thin and broad interpretation. Let's dive a little deeper.
First, What Is a Fever?
A fever is not only about the body becoming too hot.
During many infections and inflammatory processes, immune signaling molecules including interleukin-1, interleukin-6, tumor necrosis factor and other mediators participate in signaling that ultimately increases production of prostaglandin E2, or PGE2, within the central nervous system. PGE2 acts within thermoregulatory areas of the hypothalamus and raises the body's temperature set point.
One way to understand this is to think about the thermostat in your house. If the room is 68°F and you change the thermostat to 72°F, the heating system no longer considers 68°F warm enough. It begins producing and conserving heat until the new temperature is reached.
Something similar occurs during the development of a fever. A person's temperature may already be elevated, but if the hypothalamic set point has moved even higher, the body can respond as though it is cold. Blood vessels in the skin constrict to conserve heat, muscles may begin shivering to generate additional heat, and the person may reach for blankets despite already having an elevated temperature.
This is why someone with a fever can genuinely feel freezing cold. The body is not confused. It is attempting to reach its newly established temperature set point.
Why Do We Sweat When a Fever “Breaks”?
As an illness progresses and our thermoregulatory set point begins moving back toward normal, the situation reverses. The body starts to recognize its current temperature is too warm for the newly lowered set point. Peripheral blood vessels dilate, blood flow to the skin increases, sweat glands become active, and heat begins moving away from the body's core toward the surface where it can be dissipated.
This is why sweating so often accompanies the resolution of a fever. It also gives us a more useful framework for understanding traditional diaphoretic practice. Rather than imagining that an herb forces a fever out through the skin, we can consider the relationships among peripheral circulation, vascular tone, warmth, fluid movement, tension, perspiration and the body's own thermoregulatory processes.
A Fever Is Not the Same Thing as Hyperthermia
Fever and hyperthermia are sometimes discussed as though they are the same thing, but physiologically they are quite different. A fever involves a regulated increase in the hypothalamic temperature set point. Hyperthermia does not.
With hyperthermia, heat production or environmental heat exceeds the body's ability to dissipate that heat. Heat exhaustion, heat stroke and certain medication or drug-related reactions can produce dangerous elevations in body temperature without the regulated set-point change that characterizes fever.
Traditional herbal use of diaphoretics during ordinary febrile respiratory illnesses should never be interpreted as a treatment strategy for heat stroke or hyperthermia. Those situations require appropriate medical care.
A Fever Is Part of our Normal Immune Response
Fever is often approached as a something that makes us uncomfortable, but it is also part of a coordinated response to illness. Changes in body temperature can influence immune-cell activity, microbial replication and numerous aspects of inflammatory signaling.
A fever is a physiological response occurring because something is happening in the body. It is an indicator to pay attention and observe. The thermometer gives us a number, but the person gives us the rest of the story.
If someone has a fever, we might ask....."Are they alert and responsive? Are they drinking and urinating? Are they breathing normally? Are they confused or unusually lethargic? How long has the fever been present? What other symptoms are occurring? Is this an adult, a young child, an infant, an older person, or someone with medical vulnerabilities?" These questions often tell us far more than the temperature alone.
Not Every Fever Fits the Same Pattern
This is where herbal energetics comes in. Traditional Western herbalism often describes diaphoretics broadly as either stimulating or relaxing, but plants do not always fit perfectly into tidy boxes.
Stimulating diaphoretics tend to be warming, aromatic, pungent or circulatory. Traditionally, they were considered when someone appeared chilled, constricted or poorly warmed at the surface. Ginger, cinnamon, thyme, oregano, hyssop and garlic are examples of herbs on this warmer end of traditional diaphoretic practice.
Relaxing diaphoretics are generally approached differently. These plants were often selected when the person appeared hotter, tense, restless or dry, and when supporting relaxation and peripheral circulation seemed more appropriate. Elderflower, yarrow, peppermint, catnip and linden are commonly found on this side of the traditional discussion.
These categories overlap, and many of these herbs have actions extending far beyond diaphoresis. But, that is precisely the point. An herbal action can tell us information about a plant, but it does not tell us the entire story of that plant or when to use it.
Elderflower: A Classic Diaphoretic
Elderflower (Sambucus nigra) is one of the classic European diaphoretic herbs and has a long history of use during the early stages of colds and febrile respiratory illnesses. It is particularly interesting because its traditional use extends beyond perspiration. Elderflower has also been associated with upper respiratory catarrh and congestion, making it a logical addition to formulas when feverishness occurs alongside stuffiness and other upper respiratory symptoms.
The European Scientific Cooperative on Phytotherapy, or ESCOP, recognizes the long-standing traditional use of dried elderflower as a diaphoretic during common colds accompanied by fever and chills. Elderflower also contains a complex mixture of flavonoids, including rutin and quercetin derivatives, along with phenolic acids and aromatic constituents.
Related reading: Elderflower (Sambucus nigra): Traditional Uses, Herbal Actions & Modern Research
Yarrow: More Than a “Fever Herb”
Yarrow (Achillea millefolium) is another herb with a long history in European and North American herbal practice. Its flowering aerial parts contain a complex mixture of volatile constituents, sesquiterpene lactones, flavonoids and phenolic acids.
Yarrow is especially useful for demonstrating why herbal action terminology requires context. In addition to its traditional use as a diaphoretic, yarrow has been used as a bitter digestive herb, an astringent and a vulnerary. Describing yarrow as a diaphoretic does not mean that diaphoresis defines the plant. It simply describes one aspect of a broader traditional interpretation of the herb.
Peppermint: Cooling Aromatic
Peppermint (Mentha × piperita) Has volatile oil that contain substantial amounts of menthol and menthone, and menthol interacts with cold-sensitive TRPM8 receptors to produce the familiar cooling sensation associated with mint.
That cooling sensation should not be confused with literally lowering core body temperature. Peppermint's traditional use is more complex, with the leaf being an aromatic digestive herb that has also been used in cold and respiratory formulas for it's dispersing action.
Ginger: Warming & Dispersing
Ginger (Zingiber officinale) helps demonstrate the opposite side of the diaphoretic spectrum. Fresh and dried ginger preparations are both warming, although their constituent profiles and traditional applications are not identical. Gingerols, shogaols and related pungent compounds contribute to ginger's characteristic flavor and many of its investigated pharmacological effects.
Traditionally, ginger preparations have been used when coldness, chills and cool extremities were part of the presentation. That is a very different person from someone who is red-faced, hot, restless and already sweating heavily.
While both situations may appear somewhere in a discussion of diaphoretics, you can see that it does not mean the same herb is the best choice for both situations. This is one reason the question “What is this herb good for?” only takes us so far. The more useful question is, “In what kind of person and what kind of pattern does this herb fit the best?”
Catnip Isn't Just for Cats
Catnip (Nepeta cataria) is a traditional relaxing diaphoretic that deserves more attention than it usually receives. Cats may have claimed most of its publicity, but humans have been using it for a very long time too.
Traditionally, catnip has been used as a gentle aromatic nervine and diaphoretic, particularly when restlessness or digestive tension accompanied an acute illness. From a traditional formulation perspective, that combination of actions makes sense. Someone who is uncomfortable, tense and unable to settle during an illness does not necessarily need a stronger and stronger “fever herb.” Sometimes a gentle aromatic plant taken as a warm infusion fits the person far better.
Boneset: A Traditional North American Diaphoretic
Boneset (Eupatorium perfoliatum) has a long history in North American herbal medicine and was used by Indigenous peoples before becoming an important herb in nineteenth-century American medical practice. Older names such as feverwort, agueweed and sweating plant reflect its historical association with febrile illness. Traditionally prepared as a hot infusion, boneset was associated with fever accompanied by chills, respiratory symptoms and the deep muscular or “bone-like” aching that can occur during flu-like illnesses. At larger amounts, however, boneset can cause nausea, vomiting and diarrhea, and the emetic doses described in some historical literature are not appropriate for ordinary modern use.
Boneset also requires more caution than many of the gentler diaphoretics. Modern analysis has detected potentially hepatotoxic dehydropyrrolizidine alkaloids (PAs) in Eupatorium perfoliatum, including in some hot-water and alcoholic preparations. Because PA concentrations appear to vary considerably among samples and concerns include cumulative liver toxicity, boneset is not an herb I consider appropriate for frequent or prolonged internal use. I would also avoid it during pregnancy and lactation and use particular caution in anyone with liver disease. Its traditional importance as a North American diaphoretic deserves recognition, but so does the newer safety information available to us today.
Why Hot Tea Matters
One aspect of traditional diaphoretic practice that is easy to overlook is the preparation itself. Many diaphoretic herbs were administered as hot infusions.
A warm liquid supplies fluid while also warming the mouth, throat and gastrointestinal tract. It can provide volatile aromatic constituents from herbs such as peppermint, thyme, catnip and elderflower, while the warmth of the preparation may influence the subjective experience of chills and comfort. Drinking a hot herbal infusion while resting beneath a blanket creates a very different experience from swallowing a room-temperature capsule.
Sometimes we become so focused on finding the “active constituent” that we forget the cup of tea itself is part of the intervention. The preparation has always been part of herbal medicine.
The Traditional Elderflower, Yarrow and Peppermint Combination
One of the best-known traditional Western fever-tea combinations contains elderflower, yarrow and peppermint. Variations of this combination have circulated through Western herbal practice for generations.
What makes the formula interesting is not that all three herbs supposedly do exactly the same thing. Elderflower brings its traditional affinity for febrile upper respiratory conditions. Yarrow contributes its bitter, aromatic and traditional diaphoretic actions. Peppermint contributes volatile aromatic constituents and its characteristic cooling sensation.
Taken together as a hot infusion, the formula demonstrates one of the more important principles of traditional herbalism: we formulate around patterns rather than simply chasing symptoms with individual herbs.
What Modern Research Can and Cannot Tell Us
Diaphoretic herbs are an area where traditional herbal practice is considerably further along than the modern clinical research. We have extensive historical documentation of plants being used in this way and modern research explaining human thermoregulation, and phytochemical and pharmacological on many of the individual herbs. What we do not have is a large body of high-quality clinical trials demonstrating that herbs that are classified as diaphoretic predictably increase sweating, shorten fevers, or changes the course of an acute illness.
When a Fever Needs More Than Herbal Support
Fever can accompany minor, self-limiting infections, but it can also accompany serious illness. Medical evaluation may be appropriate for very high or persistent fever, fever in young infants, difficulty breathing, confusion or altered mental status, stiff neck, seizure, significant dehydration, severe headache, unusual rash, persistent vomiting, significant weakness or other concerning symptoms.
Age, pregnancy, immune status, medications and underlying medical conditions can all change the level of concern. Herbs should never become a reason to delay appropriate evaluation when the overall clinical picture suggests something more serious is happening.
An Herbalist's Perspective
Diaphoretics are a good example of why I think herbal actions are much more useful when we understand them rather than simply memorize them. It is easy to memorize that elderflower, yarrow, peppermint and ginger are all described as diaphoretics and still have very little idea what to do with that information.
Looking for patterns and observing the ill person and asking if this and uncomplicated illness appropriate for home support in the first place?
That is where herbal actions become clinical thinking rather than vocabulary words.
References
Aronoff, D. M., & Neilson, E. G. (2001). Antipyretics: Mechanisms of action and clinical use in fever suppression. The American Journal of Medicine, 111(4), 304–315.
European Medicines Agency. Achillea millefolium L., herba (Millefolii herba): European Union herbal monograph and assessment report.
European Medicines Agency. Mentha × piperita L., folium (Menthae piperitae folium): European Union herbal monograph and assessment report.
European Scientific Cooperative on Phytotherapy. (2013). Sambuci flos: Elder flower, Sambucus nigra L. ESCOP monographs.
European Scientific Cooperative on Phytotherapy. Millefolii herba: Yarrow, Achillea millefolium L. ESCOP monographs.
Walter, E. J., Hanna-Jumma, S., Carraretto, M., & Forni, L. (2016). The pathophysiological basis and consequences of fever. Critical Care, 20, 200.
About the Author
Sherri Stickler, RH (AHG) is a Registered Herbalist, former Registered Respiratory Therapist, educator, writer, and founder of Synergy Herbal Works in Tennessee. She began her herbal practice in 2014 and has worked with more than 1,000 clients. Her approach brings together traditional herbal knowledge, physiology, phytochemistry, current research, and years of hands-on experience growing, harvesting, formulating, and working with medicinal plants.
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