42. Insect Bites & Cellulitis | When the Body Remembers

In this episode of Mohivate, Dr Mohi Sarawgee explores the surprisingly complex story behind insect bites and cellulitis, following the journey from a tiny break in the skin to one of the most common bacterial infections seen in general practice.

The episode begins with something most of us have experienced. An insect bite. An itch. The temptation to scratch. But beneath that familiar story lies another, involving bacteria, the skin’s remarkable barrier, and a hidden drainage network that quietly protects us every day.

We explore why cellulitis develops, why it so often affects the legs, and the fascinating history of St Anthony’s Fire, the strange red fire that people once could only pray to survive. We look at the difference between cellulitis and the conditions that can mimic it, such as venous eczema, and the rare warning signs that should never be ignored. Along the way, we uncover the remarkable role of the lymphatic system, why cellulitis sometimes returns to the very same place, and how caring for the skin can help break the cycle of recurrent infection.

With clinical insight, practical advice, and a story that begins with a simple insect bite, this is a conversation about one of the body’s most overlooked systems, and the remarkable ways it remembers, protects, and heals.

References: 

1.The PATCH I Trial (penicillin to prevent recurrent leg cellulitis), New England Journal of Medicine: https://www.nejm.org/doi/full/10.1056/nejmoa1206300

2.NICE Guideline: Cellulitis and Erysipelas (NG141): https://www.nice.org.uk/guidance/ng141

3.British Journal of General Practice: Management of Cellulitis: https://bjgp.org/content/68/677/595

Just a gentle reminder: this episode is for information, education, and inspiration only. It’s not a substitute for your doctor’s advice. For any personal health concerns, always seek guidance from your doctor.

Transcript

SPEAKER_00 0:08

Hi everyone, welcome back to Mohivate. I'm Dr. Mohi Saraugi, a GP by profession, but here I'm swapping prescriptions for perspective. Today's topic is one I've been asked for more than almost any other by friends and quite a few of my patients, and I understand why. It's summer, the evenings are long, we are finally outside, and so unfortunately, is everything that wants to bite us. So let me start with a slightly unsettling fact about one of summer's least favorite guests. The horsefly. When a mosquito bites you, it's really rather delicate about it. A fine little needle slipped in almost politely. A horsefly has no such manners. While you think it pierces the skin, it actually cuts it with a pair of tiny blade-like mouth parts and then drinks from the wound it has made. Which is why a horsefly bite feels less like a pinprick and more like a bee sting with a grudge. And it's why these bites, more than most, have a habit of turning nasty. There's one thing I really want you to hold on to today because it's the key to this whole episode. The biting insect is almost never the real problem here. Once it bites, it's the opening it leaves behind. That tiny breach in the skin, and very often, what we then do to it with our own fingernails at 2 in the morning. That's where the real story begins. Because that little break in the skin is a door, and the ordinary bacteria already living on your skin as part of your normal skin flora will happily walk through it. Most of the time, nothing happens, but sometimes these bacteria get in deeper, and that's when a harmless summer bite becomes something with a name cellulitis. And for some people, this is the part that's most interesting, and the part we'll spend real time on. Once they've had cellulitis, they can get it again and again, often in exactly the same spot, as if that part of the body has somehow become vulnerable, marked. And there's a genuinely surprising reason why. One that has to do with a hidden drainage system in the body. So that's where we are going today. What actually happens when an insect bite gets infected? Why some people get caught in a cycle of it? How to tell the ordinary from the series, including the one red flag, I never want you to ignore. And most importantly, what you can actually do about it. So let's begin. Let's start with the bite itself. Take the mosquito. We picture a single clean little prick, but that fine needle is actually a bundle of six tiny tools. Some to pierce, some to hold the skin apart, and one to inject a little saliva that stops your blood clotting while she drinks. And yes, she, only the female mosquitoes bite because they need the protein in your blood to make their eggs. The males, meanwhile, are off drinking flower nectar, living a peaceful, blameless life. It's the expectant mothers we are up against. Now, the interesting part. That itch, that little red pump that comes after a bite is not actually a wound. It's not even really the bite at all. It's your immune system reacting to the mosquito's saliva left behind under your skin. What follows? The redness, the swelling, the maddening itch. That's your own body throwing everything it has at a few microscopic drops of insect spit. The mosquito is long gone. You are reacting to what it left behind. And that saliva, the way it quietly numbs you and thins your blood so it flows freely, is not really a mosquito thing at all. Nature has invented it over and over in creatures that aren't even related. A tick can feed on you for days and you won't even feel a thing because its saliva keeps you numb the whole time. A leech leaves a bite that keeps bleeding long after it's dropped off because its spit contains a powerful natural blood thinner. Different animals, but nature keeps landing on the same two tools. A painkiller, so you don't notice, and a blood thinner, so it flows. Once you know that, a mosquito bite feels less like an annoyance and more like a very old, very refined piece of engineering. And this is the pivot. None of that is what makes you unwell. The saliva only makes you itch. What actually makes you ill is what comes through the door afterwards. And to understand that door, you need to picture the wall because your skin is, above everything else, a brilliant living wall between you and a world that is in normal circumstances absolutely covered in bacteria. In fact, living on your skin right now, completely harmlessly, are the two most common types of bacteria called Streptococcus and Staphylococcus. They live peacefully on the surface, doing nothing at all. Because your skin is a wall and they are on the outside of it, the wall holds them back like a barrier. Everyone behaves. But break that wall, a bite, a scratch, a graze, a cracked heel, and suddenly those bacteria have a door, a vein through the barrier. Now they can get down into the deeper layers of the skin and the soft tissue beneath, where there's warmth, moisture, and nutrients, and no barrier left to hold them back. And if your body doesn't clear them quickly, they begin to multiply. And your immune system, noticing intruders exactly where they should not be, responds with everything it has. And that immune response is most of what you actually see and feel. The skin turns red, hot, swollen, and tender, and it spreads outward from the original spot. The heat and the redness aren't actually the bacteria themselves, they are your body's response to them. Blood vessels opening up, immune cells flooding in, inflammation doing its work, and it can come with other things too: a fever, chills, and feeling generally unwell. This is what we call cellulitis, a bacterial infection of the deeper skin. On the surface, it can look like a simple graze, but the real trouble is deeper down in the living tissues underneath. And it's far more common than people realize. It's one of the more frequent reasons people end up needing antibiotics and sometimes a hospital stay. Now, cellulitis can appear anywhere, but its favorite place by far is the lower leg. Hold that thought because it's not a coincidence. It's the first clue to the mystery at the center of this episode. Before we go further, I want to take you back for a moment because people have been watching this happen for a very long time. For centuries, there was a condition that terrified people. The skin would suddenly turn a deep, angry, burning red. It would feel hot to the touch and it would spread, creeping outward across the skin like something alive. They called it Saint Anthony's fire. The fire for the heat and the colour. Saint Anthony, because people prayed to him for relief, and it was said that those who prayed and recovered had been saved by him, and those who didn't weren't. There were even religious orders in medieval Europe with hundreds of hospitals devoted to caring for people burning with this fire. And here's a fascinating part. Saint Anthony's fire wasn't just one disease, it was the name given to at least three completely different conditions: a fungal poisoning from moldy grain, a viral illness we now call shingles, and the one in the same family as our subject today, the sharply bordered cousin of cellulitis that medicine calls Ericepolis. The difference, if you're curious, is mostly depth. Ericipalis sits higher in the skin with a sharp raised edge you could almost trace with a finger. Cellulitis runs deeper and its edges blur away into the surrounding skin, but they are close cousins, and for today we can treat them as one story. Three utterly different causes: a fungus, a virus, and a bacterium, all wearing the same name because to the eye they all look like skin catching fire. Medicine simply hadn't yet learned to tell them apart. I love this because it's a reminder of how young our understanding really is. For most of human history, we could see the fire, but we had no idea what was feeding it. And yet, even then, people noticed something oddly specific. They wrote that this fire drew in the neighboring parts. What they meant was that the redness didn't just sit in one spot. It travelled, spreading along the fine lines and tracks across the skin as if it were following hidden roads. They couldn't have known what they were describing, but they were pointing without knowing it straight at the real main character of this episode, the hidden system that explains why this infection for some people keeps coming back again and again. So let me introduce you to your lymphatic system. You already know about your blood circulation. The heart pumps blood out through your arteries and back through your veins. It's a loop, but running quietly alongside that loop is a second network. And to understand why it exists, you need one simple fact. When blood travels through your tissues, delivering oxygen and nutrients, it doesn't hold on to all its fluid. A little of that watery fluid constantly leaks out into the tiny spaces between your cells. This is completely normal, but that leaked fluid can't just sit there and pool, or you would slowly swell up. It has to be collected and carried back to the bloodstream. And that collecting and draining job is exactly what the lymphatic system does. It's a network of very fine vessels running throughout your body, gathering up all that leftover fluid, filtering it, and carrying it back to your blood. So think of it very simply as your body's drainage system. It's plumbing, and like all plumbing, nobody thinks about it for a single second until it stops working. It has no dramatic pump like the heart. It gets no attention, no glory. It just keeps every tissue in your body from flooding day and night for your whole life and never once asks for thanks, which frankly is the most underappreciated job in the entire body. Now here's the part that matters most today. This drainage system, apart from being a plumber, is also a key part of your immune system. Those fine vessels carry the fluid to little checkpoints along the way called lymph nodes. You know them already. They are the glands that most commonly swell up in your neck when you're ill. At those checkpoints, the body inspects the fluid for anything dangerous and clears out an infection before it spreads. So your lymphatic system is really doing two jobs at once drainage and security. And when it's working well, it clears the fluid away and keeps infection in check. But when the drainage is poor, that fluid pools, sitting warm and still, and stagnant fluid turns out to be exactly the kind of pond where bacteria love to breed. And this is exactly what happens in cellulitis. The lymphatic system gets caught in the middle of it. The infection and the inflammation reach the drainage system underneath. And that is the real question at the heart of today. What happens to that delicate drainage when cellulitis strikes? Why do so many people get cellulitis again and again? Sometimes from a simple insect bite, sometimes without any bite at all, just a tiny break in the skin. And why does it so often return to the very same place? Because there's a cruel twist to it. When you get cellulitis, the damage doesn't stain the skin. It reaches the delicate lymphatic channels running underneath and it scars them. Think of severe cellulitis as a kind of firestorm moving through the tissue. The bacteria are eventually cleared by your immune system or by antibiotics, but the fine plumbing they burn through can be left scarred and damaged, and scarred plumbing drains less well. So now you have an area of the body that drains a little less well than it used to. Fluid lingers there, the limb stays slightly more swollen, a little heavier. Doctors call that buildup of undrained fluid lymphedema, and that lingering fluid is rich in protein, which is exactly what bacteria feed on. Can you see the trap closing? The first infection scars the drainage. The damaged drainage leaves fluid pooling. That stagnant fluid makes the next infection more likely, which scars the drainage a little more, which invites the next one, and so on. This is what we call a vicious cycle. And here the phrase is almost literal. Round and round, each episode making the next one easier and often worse. And this is also why cellulitis so loves the lower leg. Gravity means fluid naturally pools there, so the drainage is already working hardest, and that's where the cycle most easily takes hold. Now, this is confirmed in the research. After a first episode of cellulitis, the risk of another within 5 years is around 1 in 4. After you've already had a repeat, it climbs to more than 1 in 2. In fact, recurrence accounts for something like 40 to 50% of all hospital admissions for cellulitis. And once the deep drainage vessels of a limb have been damaged, that area can stay vulnerable in a sense for life. So if this is you, you're absolutely not unusual and you're certainly not imagining it. Now, I don't tell you this to frighten you, I tell you the opposite. Because if the problem is a cycle, then the good news is built right in. A cycle can be broken and you can break it at more than one point. But before we get to the how, there are two things I need you to be able to recognize because getting these right is half the battle. So what I want to tell you is this a lot of what looks like cellulitis isn't, and getting this wrong leads to a great deal of unnecessary antibiotics. The most common imposter is something called venous eczema, sometimes called gravitational eczema or stasis eczema or venous stasis. Picture an older person or someone with known poor circulation in the legs. Both lower legs go red, dry, itchy, a little discolored, sometimes with a brown staining to the skin. And it may even feel a bit warm. Warm, not hot. It looks inflamed. It looks to a worried eye like infection. And so people are often given antibiotic after antibiotic for it. Sometimes month after month with no real improvement. Because antibiotics were never the answer. It was never an infection in the first place. So how do you tell them about? Three things. First, cellulitis is almost always one-sided. One leg, not both. Cellulitis in both legs at the same time is uncommon. So if both legs look the same, be suspicious it isn't an infection at all. Second, cellulitis is usually hot and tender. It hurts. That's one of the clearest dividing lines. Pain points towards infection. Itch points away from it. And third, cellulitis usually comes on fast over hours to a day or two and usually makes you feel unwell, often with the temperature. Venous eczema has usually been grumbling along for weeks or months, and in yourself, you feel perfectly fine. Now I want to be careful here. I'm not saying this so you can diagnose yourself. Please don't. I'm saying it because if you've been told you have recurrent cellulitis in both legs and the antibiotics never seem to work, it is absolutely worth gently asking your doctor the question. They may well have considered it already, but sometimes the question itself helps. Could this be a skin or circulation problem rather than an infection? Because sometimes the kindest, most useful thing medicine can do is realize it's been treating the wrong thing. Now I need to change tone for a moment because there's one thing here I never want you to ignore. The vast majority of cellulitis is straightforward. It's treated with a cause of antibiotics, it settles, and that's that. But very rarely, an infection of this same kind can be something far more serious and fast moving. An aggressive infection deeper in the tissues that is a genuine medical emergency. Its proper name is necrotizing fasciitis, and you may have heard it in the papers under a scarier name, the flesh-eating infection. Thankfully, necrotizing fasciitis is extremely rare. We are talking a handful of cases per 100,000 people. The overwhelming majority of cellulitis is just cellulitis. I want to say that clearly so nobody finishes this episode terrified of a bug bite. But because it's serious and because it's so treatable when it's caught early, it's worth knowing the one red flag that tells them apart. The single most important warning sign is this pain that is out of all proportion to how the skin actually looks. In ordinary cellulitis, the pain roughly matches the appearance. Red, sore, tender, and it makes sense. But in the dangerous version, someone is in severe escalating pain while the skin on the surface doesn't yet look bad enough to explain it. Add to that a redness that is spreading fast, visibly advancing over hours, not days, and a person who feels rapidly and severely unwell. That combination is not a see how it goes overnight situation. That is a go to hospital now, today, this hour. Pain out of all proportion to how the skin looks, spreading fast, feeling very unwell. If that's ever you or someone you love, don't wait. Trust it. Now, if the whole story starts with a breach in the wall, it's worth asking where those breaches actually come from. And here's where I get to deliver the single most undignified fact on this whole topic. We've talked about the horsefly, the dramatic bite, but the truth is bacteria don't care how glamorous the entry point is. And one of the most common doorways for cellulitis of the leg isn't a dramatic bite at all. It's athlete's foot. That mild, itchy, flaky fungal infection in the soft skin between your toes. Yes, that's often the real culprit. That little crack of split skin between the toes is a perfect quiet doorway, and the ordinary skin bacteria will happily use it to get in and travel up the leg so you can have a red, hot, swollen, genuinely serious infection climbing up your shin. And the origin of the whole drama is a bit of unglamorous fungus down between your toes that you'd barely even noticed. There is no dignity in medicine. None. Your dramatic leg infection may have been an inside job staged from your own toe. I'm being light about it, but this is a genuinely important point that people miss constantly. If you get recurrent leg cellulitis, checking for and properly dealing with athlete's foot is one of the simplest and most effective things you can do. You're shutting the door the bacteria keep walking through. And the same goes for any small breach in the skin. Crack dry skin, eczema, a cut, a graze, and insect bite. Keep the skin on your feet and legs clean and moisturized so it doesn't crack. Because every one of those little openings is a door, and closing them is how you starve the cycle. And finally, for today, you can breathe out. The scary part is over. And now we get to the genuinely useful part. What you can actually do about all of this because the good news is that a great deal of it is very much in your hands. First, stop a bite becoming an infection. Don't scratch. I know it's the hardest advice in the world at 2 in the morning. But remember what we said. It's the broken skin. If you must do something, an antihistamine tablet, an anti-itch cream, a dab of calamine, or a cold pack all calm the urge far more safely than scratching does. And keep your fingernails short because the bacteria that cause cellulitis often live under the nails, and scratching is how you deliver them straight into the wound. Wash a fresh bite with soap and water, and if the skin is broken, a d of antiseptic and a plaster to cover it does more good than people think. And to avoid bites in the first place, cover up in the evenings when the biters are out and use a good repellent. The ones containing DEET are the best studied and they are safe for children too at the right strength. Second, catch it early. This is when knowing the signs pays off that spreading redness, warmth, swelling and tenderness, usually on one leg, sometimes with a temperature of feeling unwell. If that starts, don't tough it out. See a doctor and reasonably promptly because early cellulitis treated with antibiotics usually settles well, while cellulitis left for days is what lands people in hospital. And here's a tip that genuinely helps. Take a photo or lightly mark the edge of the redness with a pen. If it's marched past that line by the next morning, you'll know. And so will whoever's looking after you. Doctors use exactly this trick on the wards. There's no reason you can't use it at home. Third, look after the drainage, the plumbing. If you already have some swelling in a limb from previous episodes, managing that swelling directly lowers your risk of the next infection because you're draining away the very fluid the bacteria feed on. That can mean elevating the leg when you can, staying active so the muscles help pump the fluid along, and in some cases, proper compression stockings or specialist lymphedema care. If a limb of yours stays swollen after cellulitis, that is genuinely worth raising with your doctor. It isn't cosmetic, it's part of breaking the cycle. And a quick word on lymphatic massage because it's having a real moment of popularity right now. A gentle, specialized massage that encourages fluid along the drainage channels can help manage chronic swelling as part of a proper package with compression and skincare. But two honest caveats, the evidence for the massage on its own is modest, and much of the real work in that package is done by compression, not the massage. And importantly, you must never do lymphatic massage on a limb that is actively infected. During an attack of cellulitis, massage is off the table. It's a tool for the times between episodes, never during the fire itself, and best done through a properly trained therapist. And fourth, for genuinely repeated episodes, there's a medical option worth knowing about. For some people who keep getting cellulitis, despite doing everything right, doctors can prescribe a low daily preventative dose of antibiotic to hold the infection at bay. A UK trial called Patch looked at exactly this and found that a low daily dose of penicillin or an alternative if you are allergic reduces the risk of recurrence by nearly half. One honest note the protection is strongest while you're taking it and tends to fade once you stop. So it's not a permanent cure, but a way to buy some calm while the other measures do their work. It isn't for everyone, and honestly, it's not something we reach for often. It's very much a last resort. But for someone truly trapped in a relentless cycle, it can be genuinely life-changing. So if that's you, please don't just suffer through bout after bout, assuming nothing can be done. Something can ask. So here we are. That's a whole arc. A bite, a scratch, a crack between the toes, a breach in the wall, bacteria walking through a door, and a quiet drainage system that can get caught in the crossfire and remembers it. And that word, remember, is the one I keep coming back to. Because when cellulitis returns to the same place, it's really the body carrying a kind of memory, a record written into the tissue of an injury it once weathered. And I've found that oddly moving, if I'm honest, preparing this episode. The idea that healing isn't always a clean return to exactly how things were before. Sometimes a part of us that has been hurt simply asks to be looked after a little more carefully from then on. Some places just carry their history and ask for a little more tending. Whether that's a leg that once had cellulitis or almost anything else, we carry through life. So the next time you find yourself brushing away an insect bite on a summer evening, I hope you'll think differently. Not with fear or worry. Most bites are nothing, but with a little respect for your skin, for the extraordinary drainage system that spends a lifetime looking after it and for the remarkable ways the body protects us, repairs us, and sometimes remembers us. I hope today gave you a little more clarity and a little more trust in your own body. Thank you for listening. I'm Dr. Mohi. Until next time, remember this. Some parts of us carry a little more history than others. Meeting those places with knowledge, kindness, and a little less fear is one more step towards coming home to yourself.