Ruby 694 nm (Obsolete)

Status: draft compiled 2026-04-20.

The ruby laser at 694 nm was the first commercially successful hair-removal wavelength, introduced in the late 1990s after the Anderson & Parrish SPTL framework made targeted follicular destruction clinically feasible. It is now essentially obsolete for this indication, and the short explanation for why tells the reader something worth knowing about the laser-wavelength tradeoff space generally.

Why ruby was used

At 694 nm, melanin absorption is very high — higher than at 755 nm (alexandrite), 810 nm (diode), or 1064 nm (Nd:YAG). Per-pulse efficacy on dark follicles in light skin is correspondingly high, and the early ruby platforms produced visible clearance faster than the alternatives available at the time. Ruby was the fastest-clearing hair-removal laser of its generation, and on well-selected Fitzpatrick I-II patients with coarse dark hair, the results were genuinely impressive. Early long-term series (Campos VB et al 2000 J Am Acad Dermatol; Bjerring & Zachariae 1998) established ruby as an effective modality. Sources: Anderson & Parrish 1983; Campos 2000 long-term efficacy. Confidence: C2.

Why ruby was displaced

The same high melanin affinity that made ruby efficient on dark hair in light skin made it catastrophic on anything darker. Epidermal melanin absorbed strongly at 694 nm, so Fitzpatrick III and especially IV-VI patients experienced burns, hypopigmentation (often permanent), and severe PIH at fluences that would have been therapeutic with a longer-wavelength alternative. Ruby's safety envelope was narrow — essentially Fitz I-II only — and the clinical reality of US patient populations increasingly including darker-skinned patients meant the platform could not serve the market. Alexandrite 755 nm retained most of ruby's efficacy on light skin while tolerating slightly darker skin types, and diode 810 nm added still more safety margin. Within a few years of alexandrite and diode reaching commercial scale, ruby's market share collapsed.

A second factor was ruby's extremely strong pigmentation response in dark skin. Permanent hypopigmentation and hyperpigmentation combined with scarring were common in mis-classified Fitz III-IV patients treated with ruby, and the malpractice exposure for clinics that attempted to extend ruby into darker phototypes was high. Litigation concerns accelerated the transition away from ruby once alternatives were available. Confidence: C2.

Current status

Ruby lasers are still in limited use for specific indications: pigmented lesion removal (lentigines, some melanocytic nevi), blue-black tattoo removal (ruby and its Q-switched variant are efficient on blue-black ink), and some research applications. They are not in current clinical use for hair removal in any mainstream US, European, or Asian market. Second-hand ruby hair-removal systems appear occasionally in budget medical spas or in emerging markets where newer platforms are not yet available; clients encountering such a system should decline on safety grounds unless they are confident they are Fitzpatrick I-II and the operator is experienced. Confidence: C3.

What the ruby story illustrates

The ruby trajectory is the cleanest historical illustration of the central wavelength-safety tradeoff in SPTL. Higher melanin affinity is faster and more efficient on matched hair, but it narrows the safety envelope for skin pigmentation. Longer-wavelength lasers sacrifice some per-pulse efficacy for a wider skin-type envelope. The evolution of the modality through alexandrite, diode, and Nd:YAG traces this tradeoff being optimised for increasingly diverse patient populations. Ruby was not wrong for its original indication, it was specialised for a narrower indication than the market demanded; the shift to 755-1064 nm wavelengths is not a scientific advance over ruby but a commercial response to the patient population's actual Fitzpatrick distribution.