At first glance, luminous combs, which are supposed to stimulate hair growth, seem to belong without doubt in the corner of ineffective quackery. But in fact: The stimulating effect of laser light on hair follicles has been proven. It was discovered by chance in the 1960s when a Hungarian physician irradiated mice with red laser light to investigate a possible carcinogenic effect of recently developed lasers. The mice did not get cancer – but apparently the hair grew faster and thicker in the irradiated areas of their shaved backs than in the surrounding skin areas .
Since then, effects of laser light on hair growth have been repeatedly proven in animal experiments and scientific studies with human volunteers. As a “paradoxical hypertrichosis”, they are also a conceivably undesirable side effect of laser depilation treatments .
Low-level laser therapy for Hair Growth
The so-called low-level laser therapy (LLLT) with red light is one of the therapies against androgenetic hair loss considered by many physicians as potentially useful  It can be used alone or in combination with minoxidil or finasteride and offers a real chance of regeneration of thinned out scalp hair. However: The phenomenon is not yet well understood, there is still no consensus on the wavelength and intensity of the laser light to be used. How exactly laser light stimulates the re-entry of telogen follicles into the growth phase and the transformation of vellus into terminal hair follicles is not yet known.
Nevertheless, the HairMax laser light comb was the first medical device for performing LLLT to be approved by the American medical authority FDA in 2007: It can be used in regular home use for the treatment of androgenetic alopecia. In addition to various models of the HairMax comb, a HairMax hair band and the iGrow laser helmet are now available from another manufacturer. The devices differ in the number of light sources and the intensity of the red light used; iGrow uses LEDs in addition to laser sources. Super Lizer, a hand-held device for use in dermatological practice, works with polarised, pulsed laser light and is mainly used for alopecia areata.
The application studies are very positive throughout: In most studies, a clear majority of the test persons (by 90 percent!) showed a moderately or even significantly increased hair density, thicker hair shafts and an increased proportion of anagen hair after approximately six months of application of laser combs or helmets without flanking treatment measures (i.e. especially without minoxidil or finasteride), whereas treatment with placebo devices (small light bulbs instead of lasers and LEDs, or LEDs of other light wavelengths) had no such effect in any study .
Since there are no comparative studies and only small studies on the effectiveness of the different devices, no recommendation can be made for a specific device.
LLLT devices cost on average several hundred dollars. However, this is a one-off expense – so a comparative assessment with long-term use of minoxidil or finasteride is more favourable than it might initially appear. Moreover, as far as is known today, the treatment is completely free of side effects. The only conceivable potential risk is that possibly existing “sleeping” abnormal skin cells in the treated skin could be stimulated in their growth by the laser light. However, no such problems occurred in the test persons of studies carried out so far.
Implementation of the LLLT treatment
The recommendations for use of different devices for domestic use may differ. In general, use is recommended approximately every other day: With a laser comb, the hair should be combed slowly for ten to twenty minutes. Hand-free appliances (helmets, etc.) should be worn for a certain amount of time (usually a few minutes).
Visible results can be expected at the earliest after three months of regular use  Positive results are likely to be maintained only if the application is continued indefinitely.