Why is low-level laser therapy safe – and why do you still need this article?
Low-level laser therapy (photobiomodulation) is one of the gentlest physiotherapy methods: the treatment does not burn, cut or damage tissue; the light energy supports cell function. Decades of research literature consistently report an extremely low risk of side effects.1 This is exactly where most people go wrong: because it feels “completely harmless”, they leave the instructions unread and miss the few situations in which treatment is not suitable – or may only be used after consulting a doctor.
In this article, you will find all contraindications divided into two levels, the possible side effects, and the rules for eye protection and laser classes – it is worth reading the whole article before buying a device and before your first treatment.
Key point
Three rules protect you from almost every problem: laser light must NEVER be directed into the eyes; an area affected by cancer or suspected cancer, and its immediate surroundings, must NEVER be treated at home; and the dose must not be increased without guidance – according to research, ineffective treatment is more often caused by overdosing than underdosing.2 All other contraindications come after these – and most are not a ban, but a matter of “ask your doctor first”.
Absolute contraindications – when must low-level laser therapy NOT be used?
These three situations are not a matter of weighing up the options – home laser treatment is ruled out in these cases:
- Light directed into the eyes – laser light can damage the retina; the treatment head must never point towards the eyes, the eyes must be kept closed when treating around the eyes, and protective eyewear is mandatory with a class 3B device
- An area affected by a known malignant tumour or a suspected tumour lesion – home treatment is ruled out; laser therapy may be considered as supportive treatment for people with cancer only under oncological supervision
- An area affected by an active purulent infection – increased local circulation may help the infection spread; a doctor must treat the infection first
Relative contraindications – when is medical advice or caution needed?
In these situations, laser treatment is not automatically ruled out – but it should only be used carefully, generally after consulting a doctor and avoiding the specified areas:
- Pregnancy – treatment of the abdomen and lower back should be avoided; other body areas should only be treated after medical consultation
- Photosensitive epilepsy – pulsed light may trigger a seizure; use only with the treating doctor's permission and in a non-pulsed mode
- Pacemaker or implanted electronics – the light itself does not interfere with the electronics, but treatment directly over the heart should be avoided as a precaution, and laser therapy must not be combined with electrotherapy
- Thyroid area – direct treatment of the front of the neck should be avoided
- Bleeding tendency or anticoagulant treatment – do not treat an area with fresh bleeding or bruising; otherwise, consult a doctor
- Acute phase of a recent injury – wait with treatment for the first 24–48 hours, while swelling is still developing; after that, laser therapy is specifically a tool of the healing phase
- Medicines that cause photosensitivity – some antibiotics (tetracyclines, fluoroquinolones), amiodarone, some diuretics and dermatological medicines may make you sensitive to light; check the patient information leaflet and ask your pharmacist if in doubt
- Tattoo, mole or heavily pigmented area of skin – dark pigment absorbs light and may heat up; leave tattoos and moles outside the treated area, and have a changing mole examined by a dermatologist first
Can it be used in children?
Low-level laser therapy is also used in children – but at home only on medical advice and under supervision. A musculoskeletal complaint in childhood may be caused by a growth-plate problem, which an orthopaedic specialist must clarify first; the dose must also be adjusted to the child's smaller body size. Eye-protection rules must be applied even more strictly in children – the device is not a toy and should not be left within reach.
Possible side effects – and what to do if they occur
| Symptom | Frequency | What to do |
|---|---|---|
| Mild warmth in the treated area | Common – normal accompanying effect | Nothing – it is not a fault and is not required for the treatment to work |
| Temporary skin redness | Occasional | It clears on its own; if it persists, reduce the treatment time |
| Temporary worsening of symptoms after the first treatments | Rare | Reduce the dose and take a 1-2 day break – I wrote a separate article about this: why pain may increase at the start of treatment |
| Mild dizziness or fatigue | Very rare | Rest; use a shorter treatment time next time |
| Headache when treating the head and neck area | Rare | Reduce the treatment time and dose |
Side effects of low-level laser therapy are mild and temporary – research reviews have consistently found this.1, 4 What is NOT normal: severe or worsening pain, blistering or a persistent skin change in the treated area – in these cases, stop treatment and contact a doctor.
Laser classes, eye protection and dosing – your daily safety routine
Laser class is not a quality ranking but a safety category. Class 1 devices (such as the B-Cure range) are designed to be safe for the eyes during intended use and can be used without protective eyewear. Class 3B devices (typically 200–500 mW point lasers) are stronger and intended for deep-tissue treatment – protective eyewear and disciplined treatment practice are mandatory. I explain which class of device to choose in the low-level laser therapy guide.
Dosing is also a safety issue. The dose-response curve in phototherapy is bell-shaped: a dose that is too low “does nothing”, the right dose supports cell function, while too much can inhibit it – researchers specifically concluded that unsuccessful treatment is more often caused by overdosing than underdosing.2 The logic of “if 5 minutes a day is good, then 20 must be even better” does not work here: follow your device's dosing table.
My advice – the 5-point daily routine
Before every treatment, run through this checklist:
- I treat clean, intact, dry skin;
- the treatment head never points towards the eyes; with a class 3B device, I wear protective eyewear;
- I follow the prescribed time and dose – neither halving nor doubling them;
- I avoid tattoos, moles and the front of the neck;
- when starting a new medicine, I check whether it causes photosensitivity.
These five points take only seconds to check – and cover almost all practical risks of home laser use.
Frequently asked questions
Low-level laser therapy uses light, not electric current or a magnetic field – it does not interfere with the pacemaker electronics themselves, so treatment of the limbs and joints is generally not a problem. Follow two rules: do not treat directly over the heart as a precaution, and do not combine laser therapy with electrotherapy (TENS, EMS) – the latter is prohibited with a pacemaker. If in doubt, follow your cardiologist's advice.
Leave this decision to your oncologist. Research is reassuring: studies of phototherapy used under specialist supervision to ease the side effects of cancer treatment have not found a tumour-safety problem3 – but this was a controlled medical setting.
As a home-use rule, follow this: during active cancer, any laser treatment requires the treating doctor's approval, and an area affected by a tumour or metastasis must never be treated.
It is not prohibited – but think about the order of events. Do not treat a fresh bruise or haematoma until your doctor has examined it; anticoagulant treatment alone is not a barrier to treating chronic joint or muscle complaints.
What to watch for: if you notice unusual bruising or swelling in the treated area, stop and tell your doctor – this may relate to your medication, not the laser.
Tattoo pigment absorbs light – there, the light energy does not reach deeper tissue but turns into heat in the skin: treatment will be ineffective and may cause unpleasant warmth or even skin irritation. The solution is simple: place the treatment head BESIDE the tattoo and find un-tattooed skin over the point to be treated.
The same applies to larger moles – leave them out, and have a changing or growing mole examined by a dermatologist regardless of laser treatment.
You can check in two places: in the “side effects” section of the patient information leaflet, look for the words “photosensitivity” or “photosensitisation”, or ask your pharmacist – they can check the databases. The most commonly affected groups include some antibiotics (tetracyclines, fluoroquinolones), amiodarone, some diuretics, retinoids and St John's wort preparations. If you take any of these, discuss laser treatment with your doctor for the duration of the course.
What does research say about safety?
“Is this method really so safe?”
According to a widely cited review that established the basis for the field, low-level laser therapy is based on a non-thermal, low-energy photochemical effect – it does not damage tissue and has consistently shown a mild, temporary side-effect profile in clinical studies.1 The key to safety is the same as the key to effectiveness: correct dosing and respect for the few genuine contraindications. The risk therefore lies not in the technology but in incorrect use.
“Is it true that it is also used in people with cancer?”
Yes – but it is important to understand how. An analysis covering 27 studies examined phototherapy for easing the side effects of cancer treatment (oral mucositis, lymphoedema and skin reactions) and found no indication that treatment caused a tumour-safety problem.3 However, this was targeted treatment under specialist supervision – the home-use rule remains unchanged: with cancer, only with the treating doctor's approval, and never over a tumour.
“What is the most common user error?”
It is not what most people think. A review of the dosing literature found that ineffective treatment – especially in well-perfused, mitochondria-rich tissues such as muscle and nerves – was more often caused by OVERDOSING than underdosing.2 The lesson is twofold: longer treatment is not primarily a safety risk but something that can reduce effectiveness – and anyone who follows the recommended treatment time can treat both safely and effectively.
Summary – Quick overview
Read more
Scientific sources
- Chung H, Dai T, Sharma SK, Huang YY, Carroll JD, Hamblin MR (2012). The nuts and bolts of low-level laser (light) therapy. Annals of Biomedical Engineering, 40(2), 516–533. DOI: 10.1007/s10439-011-0454-7
- Zein R, Selting W, Hamblin MR (2018). Review of light parameters and photobiomodulation efficacy: dive into complexity. Journal of Biomedical Optics, 23(12), 120901. DOI: 10.1117/1.JBO.23.12.120901
- de Pauli Paglioni M, Araújo ALD, Arboleda LPA, et al. (2019). Tumor safety and side effects of photobiomodulation therapy used for prevention and management of cancer treatment toxicities. A systematic review. Oral Oncology, 93, 21–28. DOI: 10.1016/j.oraloncology.2019.04.004
- Glass GE (2021). Photobiomodulation: The Clinical Applications of Low-Level Light Therapy. Aesthetic Surgery Journal, 41(6), 723–738. DOI: 10.1093/asj/sjab025
