Key takeaways.
- The 2022 BMJ Open review of laser trials reported no adverse events across its included studies.
- The real hazard is to the eye. Everyone in the room wears wavelength-matched protective eyewear.
- Normal side effects are warmth, mild redness, and occasionally a day of soreness.
- We do not treat over active cancer, a pregnant abdomen, the thyroid, active bleeding, or an implanted electronic device.
- Photosensitising medications change the picture. Tell us what you take.
What the trials found.
The 2022 systematic review in BMJ Open that pooled randomised trials of laser therapy in lower-limb tendinopathy and plantar fasciitis reported no adverse events across the included studies.
That is a reassuring finding, and it is worth reading precisely. It describes what happened when the treatment was delivered inside controlled trials by people who knew what they were doing. It does not mean a Class 4 laser is harmless in any hands under any conditions, which is the whole reason the safety rules below exist.
The eye is the real hazard.
Class 4 is the highest hazard category in IEC 60825-1, the international standard that classifies lasers by their degree of optical radiation hazard. At this class, the beam can injure the retina, and a reflection off a watch face or a piece of jewellery is enough to matter.
Retinal injury is not something that heals. That is why protective glasses go on before the device is switched on and stay on until it is off, for you, for your physiotherapist, and for anyone else in the room.
The glasses are filtered for the specific wavelength the machine produces, so they are not interchangeable between devices and sunglasses are not a substitute. If any clinic ever offers you Class 4 laser without eyewear, that tells you what you need to know about their standards.
Side effects that are normal, and one that is not.
Normal: warmth during the session that fades soon after, mild redness over the treated skin, and occasionally a day of feeling a bit more sore before things settle. None of these need any action beyond mentioning them at your next visit.
Not normal: a sharp, concentrated point of heat or anything that feels like burning while the treatment is happening. This is not something to tolerate politely. Say it the moment you feel it, and your physiotherapist will speed up the pass rate or move the handpiece. This is exactly why the head is never held still.
Also worth reporting: pain that is new, sharp, or persistent in the days after a session. Call the clinic rather than waiting for your next appointment.
When we will not use it.
These are the situations where we decline to apply laser over the area in question. Most are about caution in the absence of good evidence rather than documented harm, and caution is the correct default in that situation.
- Over an active or suspected cancer. Laser increases local cellular activity and blood flow, and directing that at malignant tissue is not supported.
- Over the abdomen or lower back in pregnancy. Safety for a developing pregnancy has not been established.
- Over the thyroid gland. A standard precaution in physiotherapy practice.
- Over an implanted electronic device such as a pacemaker or a spinal cord stimulator.
- Over active bleeding, infected skin, or undiagnosed skin changes. A skin lesion nobody has looked at needs a diagnosis before it needs a treatment.
- Over active growth plates in growing children.
A contraindication over one area does not necessarily rule out treating a different one. A pacemaker does not prevent treating an ankle. Those calls get made individually during your assessment.
Tell us what you take.
Some medications make skin considerably more sensitive to light. Certain antibiotics, some acne treatments, and drugs used in photodynamic therapy all fall into this group. On a photosensitising medication, skin can react more strongly than expected to light exposure.
Bring a current list of what you take to your assessment. It is a thirty-second conversation that changes whether the laser is the right tool, and it is easier to have before treatment than to work out afterwards.
Who is operating the machine.
Safety with a Class 4 device is mostly about the person holding it: whether they screen you properly, keep the head moving, enforce the eyewear rule, and know when not to use it at all.
Laser at Medstar is delivered by physiotherapists registered with the College of Physical Therapists of British Columbia. You can look up any of our clinicians by name in that public directory, and you can read their credentials on our team page.
Frequently asked questions.
Is high intensity laser therapy safe?
High intensity laser therapy is safe when delivered by a trained clinician with protective eyewear worn by everyone in the room. The 2022 BMJ Open systematic review of laser trials in lower-limb tendinopathy and plantar fasciitis reported no adverse events across the studies it included. The main hazard is to the eye rather than to the tissue being treated, which is why eyewear is mandatory.
Why is eye protection required for laser therapy?+
A Class 4 laser is the highest hazard category under IEC 60825-1, the international laser safety standard, and its beam can injure the retina if it or a reflection reaches an unprotected eye. Retinal damage can be permanent. Protective glasses are matched to the specific wavelength the device emits, so ordinary sunglasses provide no meaningful protection and cannot be substituted.
What are the side effects of laser therapy?+
The usual side effects of high intensity laser therapy are mild and short-lived: warmth over the treated area during and shortly after the session, and occasionally slight redness of the skin. Some people notice a temporary increase in soreness for a day. Sharp pain or a burning sensation during treatment signals that the settings need adjusting immediately, so tell your physiotherapist the moment you feel it.
Can laser therapy burn your skin?+
A burn is possible if a high-power laser is held stationary over one spot, which is precisely why the handpiece is kept moving in continuous passes throughout the treatment. Moving the head spreads the energy so no single point of skin heats excessively. If you feel a concentrated hot spot at any moment, say so and your physiotherapist will speed up the pass or reposition.
Who should not have laser therapy?+
We do not apply high intensity laser therapy over an active cancer, over the abdomen or lower back during pregnancy, over the thyroid gland, over an area that is actively bleeding, or over an implanted electronic device such as a pacemaker. We also avoid treating skin that is infected, broken, or has undiagnosed changes. Tell your physiotherapist about any of these before treatment starts.
Can I have laser therapy if I am pregnant?+
We do not treat over the abdomen or lower back during pregnancy. Laser has not been established as safe for a developing pregnancy, and the appropriate response to an absence of evidence in this situation is caution rather than assumption. Treatment of an unrelated area, such as a shoulder or an ankle, is a conversation to have with your physiotherapist and your maternity care provider.
Does laser therapy affect cancer or tumours?+
We do not apply laser over a known or suspected active cancer. Laser therapy increases local cellular activity and blood flow in the treated tissue, and directing that at malignant tissue is not something the evidence supports doing. If you have a current or past cancer diagnosis, tell your physiotherapist during your assessment so the treatment area and approach can be planned around it.
Is laser therapy safe with a pacemaker?+
We do not apply high intensity laser therapy directly over an implanted electronic device such as a pacemaker or a spinal cord stimulator. Treatment of a distant area may still be appropriate depending on the device and the site involved, and that decision is made during your assessment. Always tell your physiotherapist about any implanted device before any modality is used.
Can medications affect laser therapy?+
Some medications increase how sensitive your skin is to light, including certain antibiotics, acne treatments, and drugs used in photodynamic therapy. If you take a photosensitising medication, your skin may react more strongly than expected to the treatment. Bring a list of your current medications to your assessment so your physiotherapist can adjust the plan or choose a different approach.
Is laser therapy safe for children?+
Laser can be appropriate for adolescents with sports injuries, and we assess each case individually rather than applying a blanket rule. We avoid treating over active growth plates in growing children. For a young athlete, the more useful conversation is usually about load management and training volume, since those are what drive most growth-related injuries in that age group.
Sources.
- Efficacy of low-level laser therapy in patients with lower extremity tendinopathy or plantar fasciitis: systematic review and meta-analysis of randomised controlled trials. BMJ Open, 28 September 2022
- IEC 60825-1: Safety of laser products, equipment classification and requirements
- College of Health and Care Professionals of BC: public registrant directory
Sources checked 4 September 2026.
Not sure laser is the right tool?
Book an assessment. We'll tell you honestly whether the laser helps your injury, or whether something else will do more.
Reviewed by Sanaz Davarian, PT, MSc, Owner & Director, Registered Physiotherapist, College of Physical Therapists of British Columbia (CPTBC). Medstar was the first physiotherapy clinic on the North Shore to install a Class 4 high intensity laser.
This page is for general information only and does not constitute medical advice. High intensity laser therapy is one tool among several, and it is not appropriate for every injury or every person. Nothing here is a promise of a particular outcome. Treatment suitability is determined case-by-case during clinical assessment. Physiotherapy at Medstar Sport Physio & Health is provided by physiotherapists registered with the College of Physical Therapists of British Columbia (CPTBC).