Laser hair removal settings explained

There's no settings chart in this guide, on purpose. A number that's safe on one machine can cause an injury on another. Instead, here's what each control physically does, how they affect each other, and the order to decide them in.

The five controls

• Fluence (J/cm²) is the energy delivered per unit area. It's your most direct control over both results and risk. Too low heats the follicle without destroying it; too high exceeds what the skin can tolerate.
• Pulse duration (ms) is how long the energy is delivered for. A pulse longer than the epidermis needs to cool, but within the follicle's range, keeps the heat in the follicle.
• Wavelength (nm) sets how strongly melanin absorbs the light and, with spot size, how deep it goes. 755 nm absorbs most, 810 nm sits in the middle, and 1064 nm absorbs least and reaches deepest.
• Spot size changes depth. At the same fluence, a larger spot delivers more energy at depth, so changing tips changes the treatment even if the screen looks the same.
• Repetition rate (Hz) is pulses per second. It's a rate, not a dose.

The Hz myth

You'll often hear that a lower Hz goes deeper. It doesn't. Hz controls how fast you cover an area and how quickly heat builds when you work in motion. Depth is set by wavelength and spot size.

The confusion comes from power-limited machines, where lowering the Hz lets you raise the fluence. It's the fluence doing the work, not the Hz. If you're not reaching a deep, coarse follicle, lowering the Hz alone won't fix it.

You can't change just one thing

Raise the fluence and the skin takes more heat too. Lengthen the pulse and the epidermis is safer, but go too long and the heat leaks away from the follicle. Increase the spot size and you usually need to lower the fluence. Every time you change a setting, ask which other setting you've just affected.

The order to decide in

• Wavelength, set by skin type, then adjusted for hair depth and thickness
• Pulse duration, set by hair thickness, within the limits the skin allows
• Spot size, set by target depth and treatment area
• Fluence, last: the lowest that reaches your endpoint, not the highest the client will tolerate
• Repetition rate, set by your machine's protocol and technique, never as a depth control

Why results stall mid-course

As treatment works, regrowth becomes finer. A finer follicle heats and cools faster, so the long pulse chosen at session one may now be too long. The fix is to shorten the pulse and reassess the wavelength, not to keep raising the fluence. And a completely comfortable session with little shedding and no visible endpoint usually means under-treatment, not success.

Learn it properly: Parameters and Settings

Parameters and Settings is a 15-minute online masterclass for laser technicians and for clinics training their teams. It covers each control, how they interact, stamping versus in-motion technique, reading the client, the decision order with worked examples, and adjusting across a course.

• 15-minute video masterclass
• Short quiz at the end
• Certificate of completion for every learner who passes
• £25