Chestnut Herbal School

Introduction to Immune Stimulants, Immunomodulators, and Antimicrobials

Written and Photographed by Juliet Blankespoor


The following article is an excerpt from our 1,000-hour Herbal Immersion Program, which is the most comprehensive handcrafted online herbal course out there. 

Before we dive into herbs for the immune system, we’re going to start with lifestyles for the immune system. Because herbs are really and truly the icing on the cake, whereas the day-to-day choices we make for how we want to live are the cake, so to say. The same things in life that make us feel vital, happy, connected, and energetic also make our immune cells feel perky and capable. Our emotions play a central role in the functioning of our immune systems—so much so, that there’s a whole field of science called psychoneuroimmunology. Our moods—and sense of connection—have a profound effect on our white blood cells (immune cells, such as B cells, T cells, natural killer [NK] cells, and macrophages). The feelings of stress and social isolation are some of the biggest immune “downers” out there. Stress hormones, such as adrenaline (epinephrine) and cortisol, weaken immune function. Conversely, when we are relaxed and happy, our cells produce neuronal signaling molecules such as serotonin, dopamine, and relaxin, which have a strengthening effect on the immune system.

In one study published in the New England Journal of Medicine, 420 people voluntarily snorted either a nasal spray solution containing the cold virus or one containing a placebo. The volunteers who reported feeling really stressed prior to exposure were the most likely to develop a cold, while those who reported being less stressed were more likely to effectively fight off the virus.1 Stress can also affect how our immune cells cope with the presence of cancerous cells. At least two studies have shown how stress management can increase measurable immune factors in cancer patients. One study with melanoma cancer patients had one group practice relaxation techniques for six weeks, while the control group didn’t incorporate any stress management techniques. The relaxation group demonstrated a significant increase in natural killer cell activity over the control group.2 NK cells are white blood cells that perpetually scavenge for—and destroy—any cancerous cells they find in the body. Because they are central to our body’s defense against cancer, they are often studied as a measure of cancer resilience. A similar study looked at breast cancer patients who took a stress management course for ten weeks versus a control group. Those in the stress management course demonstrated increased white blood cell counts at the end of the program, as compared to the control group.3

Usnea lichen

Usnea lichen

We all know that humans are social creatures: we depend on one another for survival and emotional support. Unfortunately, the culture of modern industrialized nations, especially the United States, downplays interdependence and instead, celebrates extreme independence and a false sense of super self-reliance. Feeling connected and like someone “has our back,” is more important to health and immunity than you might suspect. In one large study of breast cancer survivors, women who went through life without social support were four times more likely to die of cancer compared to women with very strong social connections.4 Loneliness is associated with increased cortisol levels and lowered immune profiles.5 Our human bonds do not have to be in the form of family—we can find community and friendship through our hobbies, work, support groups, volunteering, church or spiritual groups.

You’ve most likely already noticed the relationship between sleep and immunity. Anyone who has burned the candle at two ends for long enough has noticed that lack of sleep is one of the quickest ways to catch a cold.

Hibiscus Pomegranate Orange Fire Cider

Hibiscus Pomegranate Orange Fire Cider

Nutrition also plays a central role in immunity. Adequate intake of vitamins D and C and zinc are important to healthy immunity. Good sources of vitamin C include bell peppers, broccoli, Brussels sprouts, papaya, oranges, strawberries, and pineapple.6 The following foods are high in zinc: oysters (extremely high), beef, crab, and lobster, and to a lesser extent chicken, cheese, kidney beans, garbanzo beans, cashews, and almonds.7

Finally, spending time in the sunlight—with exposed skin—in the middle of the day is important for vitamin D synthesis. People with darker skin or who live far from the equator are especially at risk for vitamin D deficiency. Food sources of vitamin D are a little harder to find. They include wild salmon, sardines, fish liver oil, mushrooms dehydrated in sunlight, and to a lesser extent cow’s milk and eggs.8 Many people choose to supplement vitamin D to ensure proper intake, especially if they don’t spend much time outdoors or belong to an at-risk population, as outlined above. We explore the topic of nutrition in more detail in our Online Herbal Immersion Program.

Echinacea purpurea

Echinacea purpurea

In the Unsettling of America, Wendell Berry beautifully sums up a holistic approach to healing:

[Our bodies] are not distinct from the bodies of plants and animals, with which we are involved in the cycles of feeding and the intricate companionships of ecological systems and of the spirit. They are not distinct from the earth, the sun and moon, and the other heavenly bodies. It is therefore absurd to approach the subject of health piecemeal with a departmentalized band of specialists. A medical doctor uninterested in nutrition, in agriculture, in the wholesomeness of mind and spirit is as absurd as a farmer who is uninterested in health. Our fragmentation of this subject cannot be our cure, because it is our disease.

Spilanthes (Acmella oleracea)

Spilanthes (Acmella oleracea)

It’s important to realize that herbs aren’t always the only support you might need to combat infections, especially in the case of life-threatening or virulent infections. Honor your own wisdom and intuition, and learn the warning signs of potentially serious conditions. Cultivate the grace and discernment to recognize when conventional medical care is appropriate. It is better to be safe than sorry, and not to let any herbal idealism get in the way of healing. Parents and caregivers: You are your child’s best advocate and greatest comfort. If your doctor or health care provider says or does something that just doesn’t seem right, speak up! You have valuable insights into your child’s health that can benefit your health care provider’s decision making or diagnosis. Here are a few scenarios where we recommend you seek conventional medical care.

When to Seek Help

Please call your doctor or seek emergency medical care for any of these potentially serious symptoms:

  • Pronounced lethargy, with or without a fever. If your child is totally disinterested in playing and/or food and just seems seriously “off,” call your doctor.
  • Fever over 100.4°F (38°C) in a young baby (under three months).
  • High fever over 103.5°F (39.7°C) or persistent fever (>3 days).
  • Difficulty breathing, with rapid, shallow breathing and wheezing sounds.
  • Persistent or extremely painful earache, sore throat, severe headache, or stomachache.
  • A red streak emanating from a wound.
  • Frequent vomiting or diarrhea: If your child hasn’t urinated at least once every eight to twelve hours, they may be dehydrated. Other symptoms of dehydration include a lack of tears when crying, dry mouth, soft fontanel (soft spot on a baby’s skull), and sunken eyes. Blood in the vomit or diarrhea is also cause for concern.
  • Fever, stiff neck, and headache are symptoms of possible meningitis. A child with meningitis often exhibits only two out of the three previously listed symptoms. In babies, a bulging fontanel (soft spot) can be an indicator of meningitis or other potentially serious conditions. When an infant is crying, lying down, or vomiting, fontanels may bulge, but they should return to normal when the infant returns to a calm, head-up position. Immediate, emergency care is called for if any infant exhibits a bulging fontanel, especially with lethargy or fever.
Clearwing hummingbird moth nectaring on wil bergamot (Monarda fistulosa)

Clearwing hummingbird moth nectaring on wild bergamot (Monarda fistulosa)

Herbal Immunostimulants

This group of herbs is used on a short-term basis to address acute infections by stimulating white blood cell activity. Immunostimulants—also called immune stimulants—help the body to resist infection during the initial stages of a possible infection as well as throughout the duration of an infectious illness. You can also call on immunostimulating herbs when you’re exposed to a contagious illness. Whenever I travel by plane, I take Spilanthes to help my body cope with the higher concentration and variety of pathogens in the recirculating air of the cabin. A good number of the following herbs also possess antimicrobial activity, pulling double duty through augmenting the body’s immune response as well as directly inhibiting the pathogen.

Also called surface immune activators, these herbs have an immediate but short-lived effect on white blood cells, and thus need to be readministered frequently to maintain their effectiveness. Every one of these herbs affects the immune system uniquely. However, general modes of action include increasing phagocytosis; moderating immune communication chemicals, such as cytokines; or increasing white blood cell division and activity. Cytokines are hormone-like chemical signalers produced by a wide variety of cells, including those of the immune system, that have far-reaching effects on immune regulation. Interleukins and interferons are two classes of cytokines that you may have heard of.

In general, immunostimulants have traditionally been used short term, as they’re often overtly stimulating in nature and can result in imbalance if used for an extended period of time. Many are heating and dispersing and can be aggravating for people with hot constitutions (for example, people who run hot, are often hot-tempered or highly passionate, and prone to inflammation). Immunostimulants have the remote potential to increase autoimmunity, and although this is more the exception than the rule, they have at times caused flare-ups in people with autoimmune conditions.

 Japanese honeysuckle (Lonicera japonica)

Japanese honeysuckle (Lonicera japonica)

The following bears repeating, as it’s all too easy to “prop ourselves up” with immune stimulants while we continue to neglect the care of our body, emotions, or spirit. When we succumb to an infectious illness, it is important to examine the condition, or terrain, of the body and how the infection was able to gain footing. If we consistently ignore the basics of good sleep, nutrition, water intake, and lifestyle and dose ourselves up with antimicrobial and immunostimulating herbs, we have missed the point. Treating symptoms without changing unhealthy inputs is not a holistic approach to healing. We feature several immunostimulants in our Online Herbal Immersion Program, including echinacea, boneset, spilanthes, and Japanese honeysuckle. 


Download the PDF file .

July 2017 Safety Update: The American Herbal Pharmacopoeia recently tested forty samples of botanically-verified boneset and found that it contains low levels of potentially toxic pyrrolizidine alkaloids (PAs), specifically the alkaloids intermedine and lycopsamine. Until further testing, we recommend avoiding the internal use of boneset in pregnancy and nursing. Additionally, children under twelve years of age and those with known liver disease should avoid the internal use. Others who wish to ingest boneset internally (after researching the potential of PA toxicity on the liver) should limit the internal use to no more than one week, and preferably ingest the herb in a formula with other herbs (to limit the dosage).

August 2021 Safety Update: Boneset contains pyrrolizidine alkaloids (PAs), which can be harmful to the liver over time when ingested internally. Recent research shows that the PAs found in boneset (and other PA-containing plants) can be taken up by other plants when grown in close proximity or when comfrey is used in the garden as mulch or fertilizer. In light of this, we are recommending that boneset should not be interplanted with herbs or food plants in the garden that will be ingested or used as mulch or fertilizer to err on the side of caution. However, mature compost that includes boneset does not seem to contain PAs once it has been fully composted according to this study.

Herbal Immunomodulators

These herbs are traditional tonics for supporting the immune system and are slower acting with a more prolonged effect as compared to immunostimulants. Also called deep immune tonics, or immune amphoterics, they are used for longer periods of time and have a more balancing rather than stimulating effect on the body. As tonics, they aren’t overtly heating or stimulating and match a wide variety of constitutions. Examine each herb for its traditional usage and constitutional picture to find the remedy with the greatest affinity for each person.

Therapeutically, these herbs are used to address low immune resilience, for example, individuals who experience frequent infections. Herbal immunomodulators are also used when the immune system is overactive, as is the case in allergies and autoimmunity. This seemingly dualistic nature can at first glance appear unbelievable, especially to those familiar with the unidirectional action of pharmaceuticals. First off, consider that most plants contain thousands of bioactive compounds: there is an immense synergy involved with each herb’s complex biochemistry. When we add the unique physiology of each human’s body into the equation, the possibilities of effects are almost infinite. Additionally, as we’ll discuss below in more detail, immunomodulators help to harmonize the endocrine and nervous systems, which, in turn, regulate immunity.

Many immunomodulators are also adaptogens, which are tonic herbs that help to support and balance the body in adapting to emotional, physical, and mental stress. (The Online Herbal Immersion Program has a whole module on adaptogens.) Herbal immunomodulators work their magic in part through the equilibration of the endocrine and nervous control of the immune system. By balancing the hypothalamic-pituitary-adrenal axis, these tonic herbs help to harmonize the control centers of the body by affecting hormonal regulation of the immune system. Another possible mode of action is the regulation of  T helper cell (Th1 and Th2) balance, which involves the equilibrium of cell-mediated (T cells) and antibody-mediated (B cells) immunity.

Astragalus membranaceus

Astragalus membranaceus

Herbal immunomodulators can be taken on a daily basis during the fall and winter months to bolster immunity and lessen the chance of succumbing to common viral infections. This class of herbs also has a role in cancer prevention and treatment; many of them are adaptogens used as adjunct therapies to conventional cancer treatments, such as radiation and chemotherapy. For cancer prevention, consider immunomodulators that are antioxidant and that act to reduce the overall inflammatory nature of the body (reducing the mutagenic potential of free radicals and the inflammatory contribution to cancer progression, respectively).

The term immunomodulation is also applied to pharmaceutical drugs in a somewhat different context. Pharmaceutical immunomodulators are predictably immunostimulating or immunosuppressive at their target site, but they have differing effects, depending on the target site. They are used to stimulate immune activity in cancer and suppress immune activity in autoimmunity and graft and organ transplants.

Note that many of the herbs listed below come from Asia, which simply reflects the cultural and governmental interest in herbal medicines in Asian nations, with the attendant funding of botanical medicine research. Cultivation of most of these medicinals in the home garden is possible, and large-scale domestic farming of many of these botanicals is already under way. Many of our tonic Western herbs used for immune support are likely to be immunomodulators as well, even if they don’t have the immunomodulating “stamp of approval.” Herbal immunomodulators covered in our online course include astragalus, ginseng, and holy basil. 


Download the PDF file .


Reishi (Ganoderma lucidum)

Herbal Immune Tonics

These herbs have traditionally been used as long-term immune tonics and most likely also possess immunomodulating effects. They are suitable for long-term use in cases of poor immunity and in cancer therapy and prevention. You may be wondering about the difference between an immune tonic and an immunomodulator. By and large, most practitioners use herbal immune tonics just the same as herbal immunomodulators. Immune tonics simply don’t have the scientific “stamp of approval” to be classified as immunomodulators, but they very well may have the same degree of regulating, or balancing, effects on the immune system.

Download the PDF file .

 Calendula flowers (Calendula officinalis)

Calendula flowers (Calendula officinalis)

Herbal Antimicrobials

Antimicrobial herbs have compounds that directly deter pathogenic bacteria, fungi, viruses, and protozoans. They are a broad class of herbs and function in many ways. Many of the following herbs are active against several classes of pathogens. For example, an herb may be both antibacterial and antiprotozoan, and another herb may be antiviral and antibacterial. It is helpful to know what kind of infection you are working with and the direct antimicrobial qualities of any herbs you are considering in the treatment of that infection.

It is interesting to note that most traditional culinary herbs demonstrate considerable antimicrobial effects, which protect against food spoilage and enteric pathogens. Having lived for years in a subtropical climate without food refrigeration, I can attest to the food-preserving qualities of raw garlic, cayenne, and oregano. In my experience, nonspiced dishes spoiled days quicker than generously spiced dishes.

Elderflower harvest

Elderflower harvest

Modern medicine has much to offer in the realm of fighting infectious organisms; antibiotics, antifungals, antiprotozoans, and similar drugs have saved countless lives. The benefit of these remedies is indisputable, but the administration must be appropriate or there can be side effects, such as diminished beneficial flora and antibiotic-resistant bacteria. Herbal antimicrobial therapies are appropriate for the common cold, the flu, and manageable mild to moderate infections. See the section in the introduction on warning signs for seeking medical care. Our Online Herbal Immersion features many antimicrobials, including goldenseal, Japanese honeysuckle, elderberry, bee balm, calendula, chamomile, lemon balm, spilanthes, rose, and yarrow.

Download the PDF file .


  1. Cohen, S., Tyrrell, D. A. J., and Smith, A. P. “Psychological stress and susceptibility to the common cold.” New England Journal of Medicine. 1991;325(9):606–612. doi:10.1056/NEJM199108293250903.
  2. Fawzy, F. I., Fawzy, N. W., Hyun, C. S., et al. “Malignant melanoma. Effects of an early structured psychiatric intervention, coping, and affective state on recurrence and survival 6 years later.” Archives of General Psychiatry. 1993;50(9):681–689.
  3. McGregor, B. A., Antoni, M. H., Boyers, A., Alferi, S. M., Blomberg, B. B., and Carver, C. S. “Cognitive-behavioral stress management increases benefit finding and immune function among women with early-stage breast cancer.” Journal of Psychosomatic Research. 2004;56(1):1–8. doi:10.1016/S0022-3999(03)00036-9.
  4. Kroenke, C. H., Kubzansky, L. D., Schernhammer, E. S., Holmes, M. D., and Kawachi, I. “Social networks, social support, and survival after breast cancer diagnosis.” Journal of Clinical Oncology. 2006;24(7):1105–1111. doi:10.1200/JCO.2005.04.2846.
  5. Uchino, B. N., Cacioppo, J. T., and Kiecolt-Glaser, J. K. “The relationship between social support and physiological processes: A review with emphasis on underlying mechanisms and implications for health.” Psychological Bulletin. 1996;119(3):488–531.
  6. “Vitamin C.” World’s Healthiest Foods website. Accessed September 20, 2016.
  7. “Zinc: Fact Sheet for Health Professionals.” National Institutes of Health website. Accessed September 20, 2016.
  8. “Vitamin D: Fact Sheet for Health Professionals.” National Institutes of Health website.

Looking for more blog articles on herbs for the immune system? We’ve compiled our most comprehensive free herbal resources on the subject, and they’re all right here for your convenience.

Meet the Green Mastermind Behind Blog Castanea:

Juliet Blankespoor

JULIET BLANKESPOOR is the founder, primary instructor, and Creative Director of the Chestnut School of Herbal Medicine, an online school serving thousands of students from around the globe. She's a professional plant-human matchmaker and bonafide plant geek, with a degree in botany and over 30 years of experience teaching and writing about herbalism, medicine making, and organic herb cultivation. Juliet’s lifelong captivation with medicinal weeds and herb gardening has birthed many botanical enterprises over the decades, including an herbal nursery and a farm-to-apothecary herbal products business. 

These days, she channels her botanical obsession through her writing and photography in her online programs, on her personal blog Castanea, and in her new book, The Healing Garden: Cultivating and Handcrafting Herbal Remedies. Juliet and her family reside in a home overrun with houseplants and books in Asheville, North Carolina.

Interested in becoming a contributor?


© Chestnut School of Herbal Medicine and, 2011-2024. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Chestnut School of Herbal Medicine and with appropriate and specific direction to the original content.

This article is an excerpt from our 1,000-hour Herbal Immersion Program, which is the most comprehensive handcrafted online herbal course out there.


29 thoughts on “Herbs for the Immune System

  1. christine Meinke says:

    Thank you for the immne builder concoction.
    Making the mushroom concoction. Wondering if lions mane is good immune stimulator.

  2. In retirement, health is wealth. My garden keeps me active, and the vitamin D from the sunlight is a bonus. I’ve learned that taking care of the basics. Sleep, nutrition, and a bit of sunshine go a long way. No shortcuts, just good vibes and a well-nurtured immune system. And you know what? Vitamin B complex is my trusted companion for maintaining that vitality in my golden years!

  3. Thank you for sharing such an informative and well-researched article on herbs for the immune system. As someone who values natural approaches to health and wellness, I found your insights to be incredibly valuable. I appreciate how you highlighted the importance of maintaining a healthy immune system, especially in the current times we live in. Your explanation of how herbs can play a significant role in supporting and strengthening our immune defenses was enlightening.

  4. says:

    Hi, I love this site and use it often as a reference! It’s an awesome course and I’m enjoying it thoroughly! I got everything printed and saved, and am trying to find where the recipes and blogs are. I was getting stagnate and forgetting much of my beginner herbal knowledge because of not having a yard or any small outside space to grow anything, and I’m doing good just to keep two plant alive. Now my enthusiasm and interest in continuing my learning and re-learning is sparked back to life again and I feel like I’m back in my body. Thank You So Much.

    • Sarah Sorci says:

      We’re so glad that you’re enjoying this material! This page offers a handy menu of topics that we cover in our blog articles. I hope this helps you find more recipes and articles that you’re looking for!

  5. I live in South Australia, are your courses available internationally? And are they recognised internationally, like by the Australian Herbalist Society etc?

    • Christine Borosh says:

      Yes, we have students all over the world including many in Australia! We offer a certificate of completion for all of our courses, which serves as an accurate representation of the time and dedication you will pour into your herbal studies. We want to be clear that we are a school of traditional herbal medicine, and we are not an accredited institution.

    • Christine Borosh says:

      The best course of action would be to see a clinical herbalist who would tailor their dietary and herbal recommendations to your constitution, lifestyle and health. Unfortunately we’re not providing consultations at this time, but there are a number of great herbalists you can reach out to. The American Herbalist Guild maintains a directory of professional herbalists, which you can access here. You can also check the Links page on our website to find graduates of our programs who do clinical work. It might be worth considering naturopathic care as well. Note that we cannot offer personal health advice due to legal restraints. We wish you the very best on your healing journey!

  6. Hi, I love this site and use it often as a reference!
    I’ve been using Astragalus and Reishi regularly in food/stocks for my family regularly this last year along with Echinacea Tincture and Elderberry Syrup at first signs of an infection or cold- its worked wonders.
    Now, I just discovered that I am pregnant again and I’d love to know your thoughts on whether these are still safe for me to use during the pregnancy.
    Thank you!

  7. Connie Ramsey says:

    I’m so excited to find your website. I have already enrolled at New England Herbal Academy, but will definitely be back here for your courses once I’ve finished. I can’t wait! 🙂

  8. Thx so much for sharing your gifts w all of us!!!. I enjoyed so much this mini class packed with so much info, some very familiar and some totally new to me. I would love to be able to print the PDFs and the bounty of information but for some extrañe reason I can’t access it from my computer. I registered from my phone and was able to access the three modules but if I try to get it from my computer it ask me to register and then says it’s closed. What can I do?
    Thx again, looking forward to join your two year program!

  9. Rahimah Martin says:

    Thank you so much for offering this course! All I’ve learned previously has been from a lot of random online research and from my friends in a home gathering. This is my first structured herb course! ~ Rahimah, in De Pere, WI

      • Rahimah Martin says:

        It’s an awesome course and I’m enjoying it thoroughly! I got everything printed and saved, and am trying to find where the recipes and blogs are. I was getting stagnate and forgetting much of my beginner herbal knowledge because of not having a yard or any small outside space to grow anything, and I’m doing good just to keep two plant alive. Now my enthusiasm and interest in continuing my learning and re-learning is sparked back to life again and I feel like I’m back in my body. Haha!

  10. loving all the wonderful information. i was wondering if there was an easy way to print?
    thank you for all your great work and sharing.

    • Sara Kinney says:

      You can try printing it directly from the website. Or if you don’t want the images, you can try to copy and paste the text into a Word document.

    • Sara Kinney says:

      Thanks, Karen! You can subscribe to our newsletter by entering your name and email address in the top right corner of this page.

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