Ruby laser (Q-switch)

The active medium of the ruby laser is a synthetic ruby crystal, which produces deep red light with a wavelength of exactly 694 nanometres. This wavelength matches almost ideally the absorption behaviour of melanin: the brown to black skin pigment absorbs the light very strongly, while water and the red blood pigment haemoglobin absorb it comparatively little – from this arises the high selectivity of the procedure.

The underlying principle is called selective photothermolysis: the Q-switching releases the energy in extremely short pulses in the nanosecond range with very high peak power – shorter than the cooling time (thermal relaxation time) of the target structure, so that only the target heats up abruptly. Pigment particles are thereby effectively burst apart (a photoacoustic effect), then cleared away by scavenger cells (macrophages) via the lymphatic system or shed with the typical crust; beneath it the upper skin layer regenerates from the surrounding healthy cells.

Age spots (lentigines, above all the lentigo solaris) arise through years of UV exposure, with an increased number of pigment-forming cells and heightened melanin production in the upper skin layer – this superficial location makes them an ideal target structure; freckles (ephelides) also respond well, but can recur under renewed UV exposure, since the predisposition remains. The high melanin affinity is at the same time the most important limitation: with darker skin types and tanned skin the risk of pigment shifts rises, which is why skin-type determination, untanned skin, adapted energy settings and, where appropriate, a test treatment are fixed components of a careful treatment concept.

The Q-switched ruby laser is among the longest-established procedures of dermatological laser therapy; the principle of selective photothermolysis is described in a scientifically sound manner and generally recognised. Controlled studies and reviews describe good efficacy with superficial, melanin-related pigment changes such as solar lentigines and ephelides, frequently with noticeable lightening or complete removal after one to two sessions. At the same time, the evidence has limits: many investigations comprise smaller patient numbers and, owing to differing device parameters, skin types and assessment standards, are comparable only to a limited extent; no pigment laser system superior for all situations can be derived from comparative studies.

Well documented are the connection between UV exposure and side effects such as post-inflammatory hyperpigmentation, and the importance of prior diagnostic clarification: dermatological specialist societies consistently emphasise that pigmented skin changes must be assessed by a specialist – generally by incident-light microscopy – before a laser treatment, and that lesions suspicious for melanoma require histological clarification; we follow this standard without exception. A guaranteed result or a complete removal in the individual case cannot be derived from the evidence – response and course are individually different.