35. Prickly Heat | When the Body Blocks What Needs to Flow

In this episode of Mohivate, Dr Mohi Sarawgee explores one of summer’s most familiar yet misunderstood conditions : Prickly Heat. A rash so common that most of us have experienced it, treated it, or complained about it without ever really understanding what is happening beneath the skin.

The episode begins with the name. Prickly heat is medically known as miliaria, from the Latin word milium, meaning millet. The story travels from Roman physicians who first described it to British soldiers itching their way through India, Southeast Asia, and the Pacific, where the rash became such a military concern that researchers eventually studied it formally in tropical conditions.

The science follows the sweat. From the remarkable efficiency of eccrine sweat glands to what happens when a sweat duct becomes blocked, Dr Mohi explores why prickly heat develops and how skin bacteria can turn a minor irritation into something far more uncomfortable. The three forms of miliaria : Crystallina, Rubra, and Profunda,  are explained clearly, including what each type means, who is most at risk, and when a doctor rather than a pharmacy is the right call.

Practical guidance covers acclimatisation, clothing, skin care, prevention, and treatment, including why the answer has never been an enthusiastic application of powder.

With clinical insight, personal reflection, humour, and a thread that runs beyond the skin itself, this episode asks a simple question: what happens when something designed to flow becomes blocked? Because sometimes the smallest discomforts are simply the body’s way of asking us to pay attention.

This episode gives prickly heat the conversation it has always deserved.

References:

1.Miliaria — StatPearls, National Library of Medicine (2024)

https://www.ncbi.nlm.nih.gov/books/NBK537176/

2.Heat Rash — Mayo Clinic

https://www.mayoclinic.org/diseases-conditions/heat-rash/symptoms-causes/syc-20373276

3.Heat Rash — NHS

https://www.nhs.uk/conditions/heat-rash-prickly-heat/

4.Miliaria — DermNet NZ

https://dermnetnz.org/topics/miliaria

5.Anhydrous Lanolin for Miliaria — Mayo Clinic Treatment Guide

https://www.mayoclinic.org/diseases-conditions/heat-rash/diagnosis-treatment/drc-20373282

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 0:07

Hi everyone, welcome back to Mohivate. I'm Dr. Mohi Saraugi, a GP by profession, but here I'm swapping prescriptions for perspective. Every season has a personality. Winter arrives quietly, wraps you up, asks nothing of you. Spring loves a compliment. Look how everything is growing. Notice me, notice me. Autumn is reflective, a little melancholy. The kind that's deeply underrated because it quietly builds something in you. Hope, perhaps. And summer, every year you tell yourself, this year you will actually enjoy it. You count down to it, you plan around it, and then it arrives that overly enthusiastic friend who doesn't understand personal boundaries, sits too close, makes everybody sweat. But wherever in the world you're listening from, you forgive it because the light is extraordinary. And for a few weeks, everything feels just a little more possible. Now, if you're in the UK, you will know that the weather until last week has been, and I'm choosing my words very carefully, confused. Grey and heavy one morning, sunshine arriving by lunchtime with the full confidence of someone who was never away. Rain by evening. In my decade of living in the UK, I have noticed one thing with great consistency. The spring bank holiday always delivers. This year, it arrived with the kind of heat that makes you check your phone twice because surely the weather app is lying. And for approximately two days, everyone was absolutely delighted. Windows open, barbecues out, optimism at an all-time high. And then, as only summer can manage, it became a little too much of a good thing. The enthusiasm, shall we say, is adjusting. And somewhere between the grey skies and the unexpected heat, something happened. While driving home from work, I saw a rainbow. After years, the kind you have absolutely no warning about. You turn on to a roundabout, and there it is. Five, six visible bands of colour, so thick and saturated that you could actually see the refraction happening. Utterly still and beautiful against a moving sky. It put the biggest smile on my face, mid-drive, the kind of smile that arrives before you've decided to smile. I came home feeling rather pleased with the universe. I had not seen a live rainbow in many, many years. And then, a few hours later, my vision board fell off the wall. Glass frame, everything shattered on the floor. There I was, dustpan in hand, vacuum cleaner on the side, on my knees, carefully picking up pieces of glass. And as I looked up, the glass had scattered into something almost prismatic in the light. And I realized my vision board had a rainbow sticker on it. I want you to appreciate the layers here. Rainbows across almost every culture and tradition are symbols of hope, new beginnings, a quiet reassurance that whatever just passed, the storm, the confusion, the gray, something better is on its way. The science agrees in its own way. A rainbow only appears when light passes through the very thing that was obscuring it. The rain doesn't disappear. The light just finds a way through. The universe apparently felt I needed to be reminded of this in the most literal way possible by making me sweep it up off the floor. I have taken this as a very clear message that it is yet again time to update my vision. I'm working on it carefully with a dustpan. Anyway, summer, the holidays, the mangoes, the ice cream, all of that, and with it the heat. And no, I'm not talking about political heat. That particular kind has found a rather permanent home and is not paying rent anywhere in particular. We leave it there. I'm talking about the kind that shows up on your skin. Prickly heat. And trust me, there is considerably more going on there than most people realize. So if you have ever wondered why you're suddenly itching in places you didn't know could itch, stay with me. Let's start with the name. Prickly heat, heat rash, sweat rash. We all use one of those, but very few use the proper name. Even as doctors, we reach for it less than you might expect. Miliaria. It comes from the Latin word millium meaning millet, a grain with tiny seeds, which is exactly what the rash looks like. Clusters of tiny seed-like bumps on the skin. The Romans named it, which means people have been itching in the heat and complaining about it since at least the first century AD. The term prickly heat is an Americanism first recorded in print around 1730. It described what soldiers, sailors, and settlers experienced when they moved from temperate climates into the tropics. The British Empire, it turns out, had a significant prickly heat problem. British soldiers stationed in India, Southeast Asia, and the Pacific spent an extraordinary amount of time being miserable. The rash became such a significant military concern that researchers formally studied it, comparing prickly heat rates in Gurkha troops versus British troops in tropical conditions. Real science, funded by the military, because soldiers who cannot stop scratching are not at their operational best. Three names, one rash. So what is actually happening inside your skin? Our skin has two types of sweat glands: apocrine glands found in the armpits and groin responsible for the kind of sweat that, shall we say, announces itself. And ekrin glands distributed across your entire body. You have approximately 2 to 4 million of them, and these are the ones involved in prickly heat. Their job is beautifully simple. When your body temperature rises from heat, from exercise, from fever, these glands produce sweat which travels up through a tiny duct like a very narrow pipe to the surface of the skin, evaporates and cools you down. Elegant, efficient. Humans are, in fact, exceptional sweaters. Compared with most mammals, our ability to sweat is extraordinary. It is one of the reasons our ancestors became such successful endurance hunters thousands of years ago, long before fans, air conditioning, or anyone thought to invent iced coffee. We survived by moving long distances while staying cool. We are in many ways professional sweaters, which is not a phrase I expected to say today, but here we are. The problem in our skin begins when that duct gets blocked. Think of it like a pipe with a blockage. When the sweat duct is obstructed by dead skin cells, by sweat residue, by tight or occlusive clothing, by skin folding against itself, as can happen with weight gain or simply the way our bodies are shaped. The sweat has nowhere to go. It cannot reach the surface, so it builds up behind the blockage, and eventually it finds the path of least resistance. It leaks into the surrounding skin tissue. Your body immediately treats this leak as an irritant. Your immune system responds, inflammation follows, and you get the rash. Prickly heat has one of the biggest image problems in medicine. Nobody posts a photograph saying living my best life with miliaria today. And yet, every year, millions of people around the world find themselves scratching away, wondering why their skin has suddenly decided to launch a small rebellion. Now, here is where it gets genuinely interesting because the blockage in that pipe is not always just mechanical. There is a bacterium called Staphylococcus epidermidis. It lives harmlessly on your skin every single day. Even right now, as you listen to this, it is part of your completely normal skin flora. But in hot, humid conditions, when the skin stays persistently damp with sweat, this bacterium forms what is called a biofilm, a sticky bacterial community that clings to the opening of the sweat duct and blocks it. Prickly heat then is at least in part a microbial problem. Your own skin bacteria in the wrong conditions becoming the architect of your misery. And it matters because the type of meliaria you have determines what you should do about it. There are three main types classified by how deep the blockage is in the sweat duct. The first is Meliaria crystallina, the mildest form. The blockage is right at the very surface of the skin. The result? Tiny clear fluid-filled blisters that look almost like water droplets sitting on the skin. They don't itch, they don't hurt, they break easily, and they resolve on their own within a day or two as long as the skin is allowed to cool and breathe. This is the type you often see in newborns, affecting up to 9% of babies in the first week of life. The reason is simple. Newborns have immature narrow sweat ducts that block very easily, especially when they are still adjusting to temperature regulation outside the womb. Their skin is also still developing its protective barrier. And here it is worth saying in many cultures, keeping a newborn warm is an act of love and care. But a baby that is too bundled, too wrapped, too close to heat for too long is a baby whose skin cannot breathe. The blisters appear quickly and they will keep appearing if the heat remains. And here is a useful clinical clue. If someone presents with a rash that looks like prickly heat but says it doesn't itch at all, tiny clear blisters, no discomfort, this is almost certainly what they have. Cool the skin, let it breathe, that is all that is needed. The second type is Meliaria rubra. This is what most people mean when they say prickly heat. The blockage is deeper in the middle layers of the skin. The result is red, inflamed, intensely itchy, prickling bumps, not clear, not fluid-filled, red, angry, and uncomfortable. This type affects up to 30% of adults who move into a hot, humid environment. 30%. That is a significant proportion of people on a beach holiday in the first week of school holidays scratching themselves while pretending to enjoy the sunshine. The third type is malaria profunda, the rarest, the deepest, the most serious. The blockage here is in the dermis, the deepest layer of the skin. The bumps are flesh-colored, firm, and resemble goosebumps, and they are associated with something genuinely important: anhydrosis, the inability to sweat in the affected area. If you cannot sweat in a significant area of your body, your body cannot cool itself properly. In extreme cases, this can lead to heat exhaustion. If someone has recurrent prickly heat, flesh-colored bumps that don't itch and notices they are not sweating normally, that is a conversation for a doctor, not a pharmacy, a doctor. And one more thing worth knowing across all three types: prickly heat can sometimes become infected. If the bumps begin filling with pus, if the skin feels increasingly hot and tender, or if you develop a fever alongside the rash, that rash may now need treatment. Sometimes antibiotics. Occasionally, if there is a fungal element involved, antifungals. If the rash is worsening despite sensible management, please see a doctor. Now prickly heat can affect anyone, but some people are more vulnerable than others. Babies and young children are at the highest risk, and we have already talked about why. Then people new to hot climates are also particularly vulnerable. Prickly heat is in many ways a disease of a climatization. The skin, the sweat glands, the entire bacterial ecosystem, all of it adapts over time. But until that adaptation has happened, the system is more prone to overload. This is why prickly heat is so common in the first week of a holiday in a hot country. Your skin is essentially still adjusting. Or in a slightly more British example, anyone who has ever landed in Tenerife in July and spent the first four days wondering why they were itching when they were supposed to be relaxing. Then people who are overweight, those who are bedbound, people who exercise intensely in the heat, and those who wear tight or non-breathable clothing are all at higher risk. And certain medications are worth knowing about. Blood pressure medications such as beta blockers and some antipsychotics can reduce the skin's ability to sweat normally, contributing to duct blockage. If you're on regular medication and find you are unusually prone to heat rash, it is worth mentioning to your GP. So, what actually works? The good news is that prickly heat almost always resolves on its own. The most effective treatment is also the simplest. Remove the cauce, cool the skin, the body will unblock the ducts given time and the right conditions. Move to a cooler environment, use a fan or air conditioning if possible. Remove excess clothing. Have a cool, not cold, shower or bath. And in the summer months, try to make that a daily habit if you can. Cold water can actually trigger rebound sweating, which is the last thing you need. Cool is the word. This reduces sweating, gives the skin a chance to clear, and begins to relieve the inflammation. Wear loose, lightweight, breathable clothing. Natural fabrics, cotton, linen, allow air to circulate and sweat to evaporate. Synthetic fabrics, tight fits, anything that traps heat against the skin, leave those behind the summer. Be careful with what you put on the skin in the affected area. Heavy moisturizers, oily products, and thick formulations can worsen things by blocking the ducts further. And sunscreen, yes, always, all year round, non-negotiable, but in the heat, look for a lighter, mineral-based formulation that sits less heavily on the surface. Now historically, people have been treating prickly heat long before anyone understood what was actually causing it. Soda bicarbonate paths, starch paths, calamine lotion, all used for generations. The cooling effect and mild alkalinity of some of these remedies actually provided genuine relief, even if nobody knew quite why. And in more dramatic cases, particularly for 19th century British administrators in places like Calcutta, the recommended treatment was simply to return immediately to a cooler climate, which, given that Britain had rather made itself at home and wasn't planning on leaving until 1947, was not always entirely straightforward or convenient. So let's look at what is available and what people reach for. If you grew up in a warm climate, chances are somebody somewhere decided the answer was powder, lots of it, an amount that suggested nobody was entirely sure what the problem was, but they were absolutely determined to cover it. Suddenly you weren't a child anymore. You were a lightly seasoned piece of fruit. Every adult involved seemed convinced that one more enthusiastic application would finally solve everything. By the end, you look less like a person and more like a Victorian ghost. The irony, of course, is that thick powder can actually block the very ducts you're trying to unblock. So while it may feel cooling in the moment, it is not doing the skin any favors. Light, non-talc-based powders used sparingly are fine. The industrial dusting, perhaps less so. Then calamine lotion, the classic pink bottle that has lived in medicine cabinets for generations, and genuinely one of my favorite things. It cools, it soothes, it relieves itching. It may not feel glamorous or modern, but it works, and I absolutely love it. Then anhydrous lanolin. This one most people have never heard of unless, of course, you have spoken to your doctor. It is one of the more interesting treatments in the literature. A waxy substance derived from sheep's wool used as nipple cream for breastfeeding mothers. So you know exactly which section of the pharmacy to head to. And whatever you identify as, you do not need to be breastfeeding to benefit from this cream. Mayo Clinic specifically recommends it for prickly heat. It has been shown in studies to reduce new lesion formation when applied before heat exposure. It works by physically preventing the duct from blocking in the first place. Worth knowing, worth remembering, and worth keeping on your shelf if this is something you genuinely struggle with. There are also times when a mild hydrocortison cream may help if there is significant inflammation present. Use it sparingly, not on the face without a doctor's advice, and not on babies without speaking to a doctor or pharmacist first. Then antihistamines that can be particularly useful at night when the itching disrupts sleep. They won't cure the rash, but they will make the experience considerably more manageable. And the single most important piece of advice do not scratch. I know, but scratching breaks the skin, introduces bacteria, risks secondary infection, and prolongs everything. Cool showers, cool compressors, calamine, anhydrouslanolin, antihistamines, these are your allies. If the rash starts filling with pus, if you develop a fever alongside it, if you have a baby who is unwell beyond the rash itself, if the skin feels increasingly hot and tender, or if you notice you're not sweating normally in the affected area, that is the point at which you need to see your doctor. You may need antibiotics, occasionally antifungals. Please do not wait. And if you're not sure it is prickly heat, because not everything that itches in summer is malaria, a pharmacist or GP can help. Eczema, contact dermatitis, fungal infections, and viral rashes can all look similar. If in doubt, always ask. And as with most things in medicine, prevention is better than cure. If you're prone to prickly heat, a few simple habits go a long way. Stay hydrated, be mindful of what you apply to your skin in the heat. Keep the skin cool and dry where you can. Choose loose, breathable, natural fabrics. And if the temperatures are already causing concern or if you're heading somewhere hot, give your skin time to adjust and perhaps keep one of those products I mentioned at home just for ease. Your skin will find its way. So here we are: the humble samarash named by the Romans, studied by the British military, suffered by millions of sweaty humans every summer. And now I hope understood a little better than before because knowing changes everything. Our skin is the largest organ in the body, a fact repeated so often it has lost its weight. So instead of saying it, let me ask you. To feel it, an organ that covers every surface of you, that regulates your temperature, protects you from infection, and senses the world around you. And when something is wrong, it does not send a politely worded letter, it simply tells you the truth. Prickly heat is the skin doing exactly that, talking. Our job, as always, is to listen and to pay attention. Because prickly heat is what happens when something designed to flow becomes blocked. And life has a habit of teaching us that lesson repeatedly. Creativity needs flow, conversation needs flow, grief needs flow, joy needs flow. Even sweat apparently needs flow. And when we ignore that for too long, discomfort has a way of getting our attention. Sometimes quietly, sometimes itchily. So as summer arrives, take care of your skin, listen when it speaks, and perhaps pay attention to the parts of your life that might be asking for a little more space, a little more movement, a little more flow. I hope this episode gave you something useful, made you smile, or simply gave you a reason to pause. Thank you for listening. I'm Dr. Mohi. Until next time, I wish you a beautiful summer. And if you're lucky enough to find a rainbow along the way, stop and look. Some things are worth paying attention to, including yourself. Because no matter how far you wander, there's always a way back home to yourself.