Laser hair removal: at 12 months, diode gave 69.2% and IPL 52.7% — **reduced, not removed**

A 2013 intrapatient, left-to-right, assessor-blinded, controlled trial in Germany. Thirty participants with skin types II–III and unwanted axillary hair had IPL assigned to one side and an 800 nm diode laser to the other, six treatments each at four-week intervals.

Because it is the same person's two armpits, skin tone, hormones and hair calibre are matched automatically. This site rates that design highly.

Hairs were counted from close-up photographs 12 months after the last treatment. The primary endpoint was reduction in hair growth, analysed on an intention-to-treat basis.

The results (from baseline, at 3 and 12 months after the last treatment):

• Diode laser: 59.7% → 69.2%
• IPL: 42.4% → 52.7%
• Both devices significantly reduced hair counts, and the diode was significantly better (P < .01).
• Pain was significantly worse with the diode — 3.7 ± 2.1 against 1.6 ± 1.4 on a visual scale (P < .01).

The important part of this item is what remained. A year after finishing all six sessions, 30.8% of hairs were still there on the diode side and 47.3% on the IPL side.

And there is another reason this trial is unusual: it counted at 12 months. Most device pages on this site stop following up at three to six months. In hair removal, 'no hair right after the session' means nothing, so this design is essential.

The 2011 study is a prospective, single-centre, bilaterally paired, blinded, randomised split-leg design. Twenty-two patients received high-fluence single-pass diode on one leg and low-fluence multiple-pass diode on the other, with hair counts at 6 and 18 months after five treatment sessions.

Two findings.

• Both techniques achieved 90–94% hair reduction, comparable to each other.
• Hair counts at six months were comparable to those at 18 months. The authors read this as meaning six-month counts can be considered indicative of long-term results.
• The low-fluence multiple-pass technique was significantly less painful.

The second line is practically useful, because it tells you when the result settles. Hair still present at six months largely stays.

The authors also wrote that the low-fluence multiple-pass approach achieves permanent hair removal with less discomfort and fewer adverse effects, especially in darker skin — a response to the structural problem that burn risk rises with skin tone.

But this is 22 people, on legs. A different site gives a different answer.

We have attached a long-term evaluation of an 800 nm diode with vacuum-assisted suction alongside; we could not confirm its detailed figures from the abstract.

Put the numbers from the two items above side by side.

• 2013 trial: 69.2% at 12 months (diode, axilla, six sessions)
• 2011 trial: 90–94% at 18 months (diode, legs, five sessions)

Same class of laser, 25 percentage points apart.

There are plenty of candidate reasons — the site (axilla against leg), hair calibre and growth cycle, participants' skin types, device settings, how hairs were counted, and sample size (30 and 22).

We cannot say which is right. Neither trial is badly designed, and they have never been compared directly.

What the gap means is this: 'laser hair removal reduces hair by X%' cannot be said without conditions. Which area, what hair, which device, how many sessions — these move the result a great deal.

Three things, though, did not change in any trial.

• The hair did not disappear. Even the best result left 6–10%.
• It takes several sessions. The trials above used five or six.
• White and blond hair are not targets for this procedure. With no melanin, there is nowhere for the light to be absorbed.