If you’ve ever hung out in a physical therapy clinic, you’ve probably seen those metal tools gliding across a patient’s tight neck, sore shoulders, or knotted hamstrings—those are IASTM tools, right? IASTM stands for Instrument-Assisted Soft Tissue Mobilization, and let’s be real, it’s become one of the go-to tools for breaking up scar tissue, easing that nagging muscle tightness, and helping athletes and regular folks get back to moving without pain. As someone who supplies these tools (I’m not just a random blogger, I actually work with the stuff day in and day out), I get questions all the time: “Does this work?” and more importantly, “What are the side effects I should watch out for?” IASTM
Most of the time, IASTM is super safe—when it’s done right. But like any hands-on therapy or physical treatment, it’s not totally risk-free. A lot of people only hear about the wins, so I wanted to break down the real side effects, the stuff you need to know whether you’re a therapist using our tools, an athlete thinking about trying it, or someone who’s just curious what goes on behind those clinic walls.
First off, let’s start with the most common, mild stuff—nothing scary, just temporary annoyances that usually fade fast. Most people describe this as post-treatment soreness, kind of like when you finish a tough workout and your muscles ache a day later. But with IASTM, it hits right after the session or the next morning, not 24 hours later. Why does that happen? When you use the tools, you’re applying pressure to break up that thick, tight scar tissue or adhesions that form after an injury, surgery, or even just years of slouching at a desk. That pressure can irritate the small nerve endings in your soft tissue, and it also causes tiny micro-tears in the muscle fibers (don’t panic—those are supposed to be good, because your body repairs them stronger). For most people, this soreness lasts 1 to 3 days, max.
But wait—some people get more than just mild soreness. Bruising is another super common side effect, especially if the therapist is going after really deep, stubborn scar tissue. Those tools are smooth, but they’re hard metal, so too much pressure can cause small blood vessels under the skin to break, leading to those dark, yellowish bruises you see a few days later. I’ve seen this happen more often on areas with thinner skin—like around the elbows, knees, or the front of the shin—than on thicker areas like the hamstrings or back. The good news is, this bruising is usually light and fades in a week or two, and it’s way less common if the therapist adjusts the pressure as they go (pro tip: our tools have rounded edges for a reason—sharp edges make bruising way more likely).
Then there’s something called skin irritation or minor rashes. Again, this is usually temporary, but it’s more common than you might think. Why? Two main reasons: first, sometimes therapists use too much of the wrong kind of lubricant, or not enough. If the tool is dragging too hard on dry skin, it can cause small abrasions—like a light, superficial scratch. Second, some people are sensitive to the lubricants we use in clinics, especially the ones with fragrances or added chemicals. I’ve had a few therapists tell me their clients got a little red, itchy patch a day after a session, and it’s almost always from the lube, not the tool itself. We always remind our customers to use a mild, unscented lotion or oil for IASTM, but it’s still something that pops up every now and then.
Now, let’s talk about the less common, but more serious side effects. These are rare, but they’re important to mention so people don’t brush them off. One is nerve irritation or even nerve damage, though that’s super rare. The nerves in your body run right under the skin, especially around joints and bony areas. If the tool is pressed too hard directly on a nerve, or is moved incorrectly, it can cause a sharp, shooting pain that doesn’t fade after the session. I’ve only heard of this a handful of times in 5 years of supplying tools—usually it’s a therapist who’s new and hasn’t learned where the safe nerve pathways are. Most of the time, it’s temporary, but in really bad cases, it can lead to numbness or tingling that sticks around for a week or two. That’s why we always tell new therapists to get proper training before using any IASTM tools—you can’t just grab a tool and start going.
Another rare but possible side effect is muscle strain or even tendon damage. Wait, I thought IASTM was supposed to help muscles, right? Yeah, but if you push too hard, too fast, on an area that’s already weak or injured, you can make things worse. For example, if someone has a partial tear in their rotator cuff, and the therapist uses heavy pressure on the surrounding muscle, they could strain the tendon even more. I’ve heard of one athlete who had a hamstring strain get worse because the therapist went too deep too soon before the original tear had healed. That’s a big reason why we include care guides with every tool we sell—they tell therapists to assess the area first, not just jump into aggressive work.
There’s also a misconception that IASTM is only for people with “bad” scar tissue, but it’s not for everyone. People with certain health conditions might have worse side effects, or even shouldn’t use it at all. For example, people with blood clotting disorders (like hemophilia) or who are on blood thinners (like warfarin) have a much higher risk of bruising and internal bleeding if pressure is applied. I’ve had a few therapists ask if they can use light pressure for these clients, and the answer is usually yes, but only with a doctor’s okay. Same goes for people with skin conditions like eczema or psoriasis—too much pressure can flare up their skin, and the abrasions from the tool can lead to infection. Oh, and pregnant people—we strongly recommend consulting an OB-GYN before using IASTM, especially on the lower back or abdomen, because the pressure can affect the growing fetus.
Wait, let’s clear up another thing: a lot of people think the side effects are just from the tool, but honestly, most of them come from technique, not the tool itself. Our IASTM tools are made from high-grade surgical stainless steel, they’re polished to be smooth, and they’re designed to glide over soft tissue without digging in. If a therapist uses too much pressure, or moves the tool in the wrong direction, that’s when the side effects happen. I’ve had a therapist tell me they got great results with our tools but had a client get bad bruising—turns out they were pressing twice as hard as they should have. Once they adjusted, the side effects stopped. That’s why we don’t just sell tools—we offer free tips and training resources for all our customers, because we know the tool is only half the battle.
I also want to talk about what you can do to minimize side effects, because that’s way more useful than just listing them. First, go to a licensed therapist who’s trained in IASTM—don’t let your friend who watched a YouTube video use the tools on you. Second, drink plenty of water after your session—your body needs water to repair those micro-tears and flush out any inflammation. A lot of people forget that, and they end up more sore than they should be. Third, don’t push through the pain during the session. If something feels like sharp pain, not just the deep “good” pressure, tell your therapist to lighten up. And fourth, avoid the area for strenuous exercise for a day or two after—let the tissue repair instead of working it hard right away.
Now, let’s be honest—no therapy is perfect. IASTM has a ton of benefits: it speeds up recovery, reduces pain, helps with range of motion. The side effects I talked about are mostly mild, temporary, and preventable if you have the right person using the right tools. But it’s important to be honest about the downsides, because not every clinic out there uses good tools or trained therapists. That’s why our tools are designed to reduce the risk of side effects—we spent years testing different shapes and finishes to make sure they’re safe for all soft tissue types, from thin neck skin to thick back muscles.
If you’re a therapist who’s looking for quality IASTM tools that come with clear care guides and support, or you’re a clinic owner who wants to stock tools that your staff can rely on, we’re here for you. We don’t just ship a box of tools and disappear—we answer questions, help with training tips, and make sure our products are up to the standards that prevent those avoidable side effects. Whether you’re new to IASTM or you’ve been using tools for years, we can work with you to find the right set for your practice.
Electrical Cupping References
- Biological Effects of Instrument-Assisted Soft Tissue Mobilization: A Systematic Review, Journal of Orthopaedic & Sports Physical Therapy, 2019
- Adverse Events Associated With Manual Therapy and Soft Tissue Mobilization: A Meta-Analysis, Physical Therapy in Sport, 2021
- Instrument-Assisted Soft Tissue Mobilization Technique and Outcome Measures: A Clinical Practice Guideline, American Physical Therapy Association, 2020
- Skin Irritation and Adverse Reactions to Soft Tissue Mobilization Lubricants, Journal of Clinical Dermatology, 2018
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