HERX vs. FLARE EDUCATION
Updated: 1 day ago
I get asked this all the time: "Am I herxing, or is this a flare?" It can be so hard to tell when you feel awful. Here is what I was taught, and what Lyme-literate doctors and research say.
Short on time or energy? A quick-view graphic with the key points is at the bottom of this post.
Looking for things that may help during a herx? See my solutions post:
My easy-to-watch herxing video:
WHAT IS A HERX?
- The full name is the Jarisch-Herxheimer reaction. Most of us just say "herx" or "herxing."
- It's a short-term worsening of symptoms that can happen after you start treating a spirochete infection like Lyme. Syphilis and relapsing fever are spirochete infections, too.
- It is not an allergy, but the two can look alike at first.
- Not everyone herxes, and that doesn't mean treatment isn't working. A 2017 review of early Lyme studies (people with an erythema migrans rash) found it in about 7% to 30% of people treated with antibiotics. Reactions in Lyme were usually milder than in the other spirochete infections.
WHY DOES IT HAPPEN?
- Treatment kills bacteria. As they break apart, they release pieces and proteins that set off the immune system.
- The immune system answers with a wave of inflammation messengers called cytokines. TNF-alpha, IL-6 and IL-8 are three of them, according to Dr. Richard Horowitz and Dr. Marty Ross.
- That surge of inflammation is why you feel worse for a while.
- Lyme-literate doctors see herxing most often when herbal antimicrobials or antibiotics are first started, when a new one is added, or when a dose goes up. Dr. Ross notes it can also happen when treating some co-infections and yeast, and that heat, like a far infrared sauna or a hyperthermic bath, can increase die-off.
- Tulane University researchers studied leftover pieces of dead Lyme bacteria in brain and nerve tissue from a primate model. The pieces caused several times more inflammation than live bacteria did. The study was about lingering symptoms, not herxing itself, but it shows how much trouble dead bacteria can stir up.
WHAT CAN A HERX FEEL LIKE?
- Your usual Lyme symptoms turned up louder: fatigue, brain fog, nerve and muscle pain, trouble with memory and thinking
- Fever, chills or shaking
- Night sweats
- Muscle aches
- Headache
- Nausea or vomiting
- Flushing, or a rash that gets worse
- A racing heart or low blood pressure
- More trips to the bathroom
WHEN DOES IT START AND HOW LONG DOES IT LAST?
- Mainstream sources describe a fast reaction. StatPearls says it shows up within 24 hours of starting antibiotics and settles on its own. Johns Hopkins says it happens early, within the first few days, and should settle within 24 to 48 hours.
- Lyme can be different. LymeDisease.org writes that a Lyme herx usually starts 48 to 72 hours after antibiotics begin and can go on for weeks.
- Many of us in the Lyme community have had herxes that lasted much longer than a day or two. My doctor says a herx lasting over 2 weeks is too long.
WHAT IS A FLARE?
- A flare is when symptoms get worse because the infection is more active, or because something else is stirring up inflammation. It isn't caused by die-off.
- Dr. Bill Rawls explains that in a flare, the microbes aren't under control and are growing more.
- Lyme symptoms often come and go in cycles. Dr. Joe Burrascano says they tend to wax and wane on about a four-week cycle, and a daily symptom diary can show the pattern. As treatment starts working, the hard days ease and good days become more common.
- Things that can trigger a flare: food sensitivities, toxins, new stress, poor sleep, travel or doing too much (Dr. Rawls); yeast, a new virus, a Bartonella or Babesia relapse, or recent mold exposure (Dr. Ross).
- Sometimes a flare means the treatment has stopped working as well. Dr. Rawls notes microbes can build a tolerance to a treatment used for a long time, and Dr. Ross lists treatment no longer working as a possible cause.
HERX OR FLARE? HOW TO TELL
They can feel exactly alike, because both come from inflammation. Timing is the biggest clue.
A HERX:
- Bacteria are dying and breaking apart.
- You feel worse soon after starting something new or raising a dose.
- With a "good herx," as Dr. Horowitz describes it, you start to feel better than before once it passes.
A FLARE:
- The infection is more active, or something else is driving inflammation.
- It doesn't line up with starting anything new.
- It often follows a trigger like stress, poor sleep, a food you react to, mold, travel or a new illness.
- Dr. Burrascano notes that after stopping treatment too soon, Lyme symptoms usually take 3 to 4 weeks to return. When someone was sick again within a week, he suspected Bartonella, which moves faster.
The question to ask yourself: Did I start or increase something right before I felt worse?
WHY IT MATTERS
- The answer changes what you and your doctor do next. A herx may mean slowing down, adding support or taking a short break. A flare may mean looking for a trigger or a co-infection, or changing the treatment.
- A herx can be confused with an allergic reaction to the medicine, and a severe herx can look like other serious problems. StatPearls stresses telling it apart from severe allergic reactions and sepsis. Your doctor is the one to sort that out.
- Dr. Horowitz describes a "bad herx" as one where you return to your old baseline afterward with no real improvement. That's worth telling your doctor about, too.
WHEN TO CALL YOUR DOCTOR
- Let your doctor know any time you feel worse after starting or changing a treatment.
- Keep a daily symptom diary when changing treatment. LymeDisease.org suggests writing down your temperature at the same time each day, plus any new or worse symptoms.
- If a reaction goes on longer than a herx usually would, your doctor may look at whether it's a drug reaction or side effect instead.
- Jennifer Crystal of Global Lyme Alliance suggests telling your Lyme doctor how a herx affects your daily life, like work or caring for kids, so you can decide together what your body can handle. Pulsing antibiotics or changing them are options she mentions.
- Dr. Burrascano has used pulsed antibiotics for people who herx badly, so the body has time to clear between doses.
GET HELP RIGHT AWAY IF:
- You have trouble breathing or your throat feels like it's swelling. These can be signs of a severe allergic reaction.
- Symptoms feel extreme. Serious reactions are rare, but LymeDisease.org advises heading to the closest ER.
MY EXPERIENCE
- We are meant to tolerate treatment, and herxing is often part of it. Some don't herx and that is great. Many do.
- When I was clearly herxing and it was tolerable, I kept going and increased my detox.
- When I was extra miserable, my doctor had me back off or take a 2 to 3 day break. I did better at restart. I hated taking breaks, but over time I learned they helped me in the long run.
- Pushing too hard isn't safe. Our bodies have to be able to clear the die-off from treatment.
To quote my doctor: "You are NOT meant to be tortured in treatment, you are meant to tolerate it. If it feels like it's too much to handle, it probably is time to back off."
A good judge for me: am I grabbing things to help and keeping going, or am I messaging the doctor constantly?
More on when to push through and when to back off:
RELATED POSTS
CYTOKINES EDUCATION
What cytokines are and why they make us feel so sick.
ORGANIZING YOUR LYME TREATMENT AND SYMPTOM TRACKING
Symptom tracker ideas that can help you spot a herx or a flare pattern.
SOURCES
Dr. Marty Ross, Herxheimer Die-Off Reaction (2025) and Is It a Lyme Disease Herx Reaction? (updated 2026)
Dr. Joe Burrascano, A Masterclass on Tick-Borne Illness, Bay Area Lyme Foundation (2025)
Wood and Sbar, Jarisch-Herxheimer Reaction, StatPearls (2025)
Johns Hopkins Lyme Disease Research Center, Treatment and Prognosis (2026)
Jennifer Crystal, Global Lyme Alliance, reader questions on herxing (2023)
Tulane University, Could long-dead bacteria be the culprit behind lingering Lyme symptoms? (2022)
Dr. Bill Rawls, Herxheimer Reaction vs. Lyme Flare-Up (2019, older source, still worth reading)
LymeDisease.org, The dreaded Jarisch-Herxheimer reaction, with Dr. Richard Horowitz's guidance (2017, older source, still worth reading)
Butler, The Jarisch-Herxheimer Reaction After Antibiotic Treatment of Spirochetal Infections, American Journal of Tropical Medicine and Hygiene (2017, older source, still worth reading)
Disclaimer: Rise Above Lyme makes no claims about any possible benefit of using any product mentioned within this site. Always consult with your doctor before adding anything. The information shared is based on personal experience, years of accumulated researched resources from Lyme Literate doctors and polls conducted within Lyme groups from actual patient experience using these solution ideas.
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