Ruby lasers for hair removal were cleared by FDA to market in the U.S. in 1997. Ruby lasers have the best published documentation of results.  Arguably the best overview is Topping.  There are also two excellent papers by practitioners on optimizing treatment parameters. [3, 4]
Studies with short-term follow-up have observed 20% to 60% reduction at 3 months. [5, 6, 7, 8] Another found a fluence-dependent relationship at a range of 38% to 49% reduction at 3 months, which compared favorably to electrolysis and waxing.  A large short-term study observed that about two-thirds of subjects had over 50% reduction at 3 months. [10, 11]
Long-term follow-up with ruby is better documented than other lasers. As discussed in the section on “permanent hair reduction,” the pilot study observed 4 of 13 patients had 42% to 60% reduction at 24 months. [12, 13]. Several studies since then have also shown a significant number of non-responders among “ideal” subjects, for reasons that are unknown. Two well-designed studies had almost identical non-response rates of 29% and 28%. Responders had apparently permanent reduction in hair color and diameter, and one observed 22% reduction 7 months after a single treatment. [14, 15] Another study had similar findings of less than 25% reduction at 6 months.after an average of 2 treatments. 
Other studies have observed better results: One found 61% reduction at 9 months after 4 treatments.  Another noted 63% of patients had sparse regrowth at 8 months. 
Several well-designed British studies by Liew and colleagues make interesting observations about ruby laser safety and effectiveness. One large study found an average of 56% reduction at an average of 6 months after an average of 2 treatments.  However:
Histological examination found damage only went to about 1.5 mm at 20 J/cm2 “The laser damage did not seem to extend far enough down the hair shafts to result in permanent hair destruction.” 
Although success was observed to correlate with hair follicle eumelanin content.  the reasons for the “unpredictable response” in laser treatment could not be attributed solely to melanin content or growth cycle.
Another series of histological examinations after treatment found damaged follicles were “randomly dispersed amongst intact follicles.”  The authors note that “the exact mechanisms of hair destruction and the potential damage to other structures of skin are not known,” which is further evidenced by recent data suggesting laser affects oil (sebum) production in almost all patients. 
One well-designed measurement of hair follicle temperature found a range from 5 – 30 degrees C. but only in those hair shafts that showed damage after treatment. This might explain the “uneven outcome.” 
Although some anecdotal observation and histological samples have suggested treated hair can come back finer in texture [13, 25], a quantified analysis found no statistically significant change in follicle diameter at 7 months . A second histological study found “no evidence of permanent follicle death” after one ruby laser treatment. [27, 28] A third study observed some follicles were clearly damaged and suggested hairs in early anagen were not affected. 
They also found no histological evidence of cellular hyperproliferation  or oxidative stress , suggesting laser is safer in comparison to UV radiation.
Although side effects are generally rare,  skin discoloration rates have been reported from 1% to 10%, with darkening being more common and often taking several months to resolve . Histological evidence shows that darker skin has higher side effects, especially hypopigmentation 
Preheating or precooling the skin before treatment may help reduce side effects. [35, 36] Lower fluences have been observed to cause higher rates of double hairs as regrowth.  As with electrolysis, there is a chance of isomorphic phenomena like trauma-induced lesions,  and, patients should avoid sun following treatment to avoid significant and persistent pigment changes to the skin lasting several months. 
Please see hairfacts.com for a list of ruby laser medical data.
Topping A, Linge C, Gault D, Grobbelaar A, Sanders R. A review of the ruby laser with reference to hair depilation. Annals of Plastic Surgery 2000 Jun;44(6):668-74.
Williams RM, Christian MM, Moy RL. Hair removal using the long-pulsed ruby laser. Dermatologic Clinics 1999 Apr;17(2):367-72.
VanderKam VM, Achauer BM. Hair removal with the ruby laser (694 nm). Plastic Surgical Nursing. 1997 Fall;17(3):144-5, 137.
Lask G, Elman M, Slatkine M, Waldman A, Rozenberg Z. Laser-assisted hair removal by selective photothermolysis. Preliminary results. Dermatologic Surgery 1997 Sep;23(9):737-9.
Solomon MP Hair removal using the long-pulsed ruby laser. Annals of Plastic Surgery 1998 Jul;41(1):1-6.
Williams R, Havoonjian H, Isagholian K, Menaker G, Moy R. A clinical study of hair removal using the long-pulsed ruby laser. Dermatologic Surgery 1998 Aug;24(8):837-42.
Sommer S, Render C, Burd R, Sheehan-Dare R. Ruby laser treatment for hirsutism: clinical response and patient tolerance. British Journal of Dermatology 1998 Jun;138(6):1009-14.
Polderman MC, Pavel S, le Cessie S, Grevelink JM, van Leeuwen RL. Efficacy, tolerability, and safety of a long-pulsed ruby laser system in the removal of unwanted hair. Dermatologic Surgery 2000 Mar;26(3):240-3.
Bjerring P, Zachariae H, Lybecker H Evaluation of the free-running ruby laser for hair removal. Acta Dermato-Venereologica 1997 77:1-4.
Zachariae H, Bjerring P, Lybecker H. Laser depilation using a free-running long pulse ruby laser. Experimental Dermatology 1999 Aug;8(4):301-2.
Grossman MC, Dierickx C, Farinelli W, Flotte T, Anderson RR. Damage to hair follicles by normal-mode ruby laser pulses. Journal of the American Academy of Dermatology 1996 Dec;35(6):889-94.
Dierickx CC, Grossman MC, Farinelli WA, Anderson RR. Permanent hair removal by normal-mode ruby laser. Archives of Dermatology 1998 Jul;134(7):837-42.
Lin TY, Dierickx CC, Campos VB, Farinelli WA, Rosenthal J, Anderson RR Reduction of regrowing hair shaft size and pigmentation after ruby and diode laser treatment. Archives opf Dermatological Research 2000 Feb-Mar;292(2-3):60-7.
Liew SH, Ladhani K, Grobbelaar AO, Gault DT, Sanders R, Green CJ, Linge C. Ruby laser-assisted hair removal success in relation to anatomic factors and melanin content of hair follicles. Plastic and Reconstructive Surgery. 1999 May;103(6):1736-43.
Wimmershoff MB, Scherer K, Lorenz S, Landthaler M, Hohenleutner U. Hair removal using a 5-msec long-pulsed ruby laser. Dermatologic Surgery 2000 Mar;26(3):205-10.
Sommer S, Render C, Sheehan-Dare R. Facial hirsutism treated with the normal-mode ruby laser: results of a 12-month follow-up study. Journal of the American Academy of Dermatology 1999 Dec;41(6):974-9.
Campos VB, Dierickx CC, Farinelli WA, Lin TY, Manuskiatti W, Anderson RR. Ruby laser hair removal: evaluation of long-term efficacy and side effects. Lasers in Surgery and Medicine 2000;26(2):177-85.
Gault DT, Grobbelaar AO, Grover R, Liew SH, Philp B, Clement RM, Kiernan MN. The removal of unwanted hair using a ruby laser. British Journal of Plastic Surgery 1999 Apr;52(3):173-7.
Liew SH, Grobbelaar AO, Gault DT, Sanders R, Green CJ, Linge C. The effect of ruby laser light on ex vivo hair follicles: clinical implications. Annals of Plastic Surgery. 1999 Mar;42(3):249-54.
Liew SH, Grobbelaar AO, Gault D, Green C, Linge C. Ruby laser-assisted hair removal: a preliminary report of the correlation between efficacy of treatment and melanin content of hair and the growth phases of hair at a specific site. Annals of Plastic Surgery. 1999 Mar;42(3):255-8.
Liew SH, Cerio R, Sarathchandra P, Grobbelaar AO, Gault DT, Sanders R, Green C, Linge C. Ruby laser-assisted hair removal: an ultrastructural evaluation of cutaneous damage. British Journal of Plastic Surgery 1999 Dec;52(8):636-43.
Manuskiatti W, Dierickx CC, Gonzalez S, Lin TY, Campos VB, Gonzalez E, Anderson RR. Laser hair removal affects sebaceous glands and sebum excretion: a pilot study. Journal of the American Academy of Dermatology 1999 Aug;41(2 Pt 1):176-80.
Topping A, Gault D, Grobbelaar A, Green C, Sanders R, Linge C. The temperatures reached and the damage caused to hair follicles by the normal-mode ruby laser when used for depilation. Annals of Plastic Surgery 2000 Jun;44(6):581-90.
Lin TY, Dierickx CC, Campos VB, Farinelli WA, Rosenthal J, Anderson RR. Reduction of regrowing hair shaft size and pigmentation after ruby and diode laser treatment. Archives opf Dermatological Research 2000 Feb-Mar;292(2-3):60-7.
Liew SH, Ladhani K, Grobbelaar AO, Gault DT, Sanders R, Green CJ, Linge C. Ruby laser-assisted hair removal reduces the coarseness of regrowing hairs: fallacy or fact? British Journal of Plastic Surgery 1999 Jul;52(5):380-4.
McCoy S, Evans A, James C. Histological study of hair follicles treated with a 3-msec pulsed ruby laser. Lasers in Surgery and Medicine 1999;24(2):142-50.
McCoy S, Evans A. A histological study of hair follicles treated with a 3 msec pulsed ruby laser. Experimantal Dermatology. 1999 Aug;8(4):352-4. No abstract available.
Omi T, Honda M, Yamamoto K, Hata M, Akimoto M, Asano G, Kawana S. Histologic effects of ruby laser hair removal in Japanese patients. Lasers in Surgery and Medicine 1999;25(5):451-5.
Liew SH, Grobbelaar AO, Gault DT, Green CJ, Linge C The effect of ruby laser light on cellular proliferation of epidermal cells. Annals of Plastic Surgery 1999 Nov;43(5):519-22.
Haywood RM, Wardman P, Gault DT, Linge C. Ruby laser irradiation (694 nm) of human skin biopsies: assessment by electron spin resonance spectroscopy of free radical production and oxidative stress during laser depilation. Photochemistry and Photobiology 1999 Sep;70(3):348-52.
Nanni CA, Alster TS. Laser-assisted hair removal: side effects of Q-switched Nd:YAG, long-pulsed ruby, and alexandrite lasers. Journal of the American Academy of Dermatology 1999 Aug;41(2 Pt 1):165-71.
Haedersdal M, Egekvist H, Efsen J, Bjerring P. Skin pigmentation and texture changes after hair removal with the normal-mode ruby laser. Acta Dermato-Venereologica 1999 Nov;79(6):465-8.
Liew SH, Grobbelaar A, Gault D, Sanders R, Green C, Linge C. Hair removal using the ruby laser: clinical efficacy in Fitzpatrick skin types I-V and histological changes in epidermal melanocytes. British Journal of Dermatollogy 1999 Jun;140(6):1105-9.
Topping A, Gault D, Grobbelaar A, Green C, Sanders R, Sibbons P, Linge C. Successful reduction in skin damage resulting from exposure to the normal-mode ruby laser in an animal model. British Journal of Plastic Surgery 2001 Mar;54(2):144-150.
Raulin C, Greve B, Hammes S. Cold air in laser therapy: first experiences with a new cooling system. Lasers in Surgery and Medicine 2000;27(5):404-10.
Ye JN, Prasad A, Trivedi P, Knapp DP, Chu P, Edelstein LM Pili bigeminy induced by low fluence therapy with hair removal alexandrite and ruby lasers. Dermatologic Surgery 1999 Dec;25(12):969.
Wimmershoff MB, Hohenleutner U, Landthaler M. Isomorphic phenomenon: adverse effect after epilation with the long-pulsed ruby laser. Archives of Dermatology 2000 Dec;136(12):1570-1.
Hasan AT, Eaglstein W, Pardo RJ. Solar-induced postinflammatory hyperpigmentation after laser hair removal. Dermatologic Surgery. 1999 Feb;25(2):113-5.
Summary of data with links to abstracts
Human clinical studies
Grossman (1996): Six months after being treated once at various energy levels, 4 of 13 ideal laser patients (light skin/dark hair) had less than 50% regrowth. These four patients were followed and reported on in Dierickx (1998), below.
Lask (1997): Twelve weeks after one laser treatment to their arms, 20 patients saw 40-80% regrowth.
Dierickx (1998): Demonstrates reduction in number of terminal hairs in 4 of 13 ideal laser patients. This widely cited study was submitted to FDA as clearance to market as “permanent hair reduction” based on these 4 patients. Recommended reading for all considering ruby laser hair removal. A follow-up to Grossman (1996), it appeared in the same journal as an overview critical of the study-- Tope (1998) below.
Solomon (1998): 72 patients received 1 to 4 laser treatments. Methodology is very vague, but at an average of 14 weeks after last treatment, patients observed reduction in hair density, with at least one patient still pleased at nine months. No quantitative data on efficacy is presented, just patient assessment.
Williams (1998): Reports on two 12-week tests, one involving 25 patients, and one involving 12 patients. Patient experiences are very detailed, but quantitative data on efficacy is lacking.
Sommer (1998): 43 pateients each had two sites treated: a site with one treatment and a site with four treatments, once a month. Observation three months after treatment showed the single-treated site with 21% reduction in hair count vs 56% reduction on the multi-treated site. Comparative 6-month data not available.
McCoy (1999): 24 patients received 1 to 3 treatments to the armpit or groin, followed by biopsies at 0 to 8 weeks. There was no histological evidence of permanent follicle death after one ruby laser treatment, but the authors conjecture that multiple treatments may alter or inhibit the growth cycle.
Hasan (1999): Reports on an unsuccessful attempt to clear up blotchy darkening of the skin (hyperpigmentation) in a laser patient who tanned her legs against doctor’s instructions.
Bjerring (1998): 133 female patients received 1 to 9 treatments (average 2), followed by at least 13 weeks of observation. At 13 weeks, 60% of patients had over 50% hair removal.
Liew (1999): 48 patients were treated once and observed at 3 and 7 months. This well-designed study demonstrated 14 non-responders, 13 temporary responders, 18 semi-responders, and 4 delayed responders. Liew also demonstrates that succes corresponds with eumelanin levels (the darker of the two types of melanin in human hair. He reports average reduction at 7 months at 22% after a single treatment.
Lin (2000): 47 patients were treated and observed either 9 or 12 months after treatment. This study showed 13 non-responders and 34 subjects with hairs that had reduction in color and diameter compared to pretreatment measurements.
Ye (1999): * Reports that low-fluence ruby treatment can cause more than one hair to grow from the same follicle (pili bigemini).
Overviews and summaries
Grossman (1997): A one-page summary.
Dierickx (1997): A brief article.
Tope (1998): This overview of clinical data takes a critical look at the problems in many laser hair removal studies, especially Dierickx (1998). Appears in the same journal issue
Williams (1999): This is a very good overview of before, during and after instructions for laser patients, from a clinician’s viewpoint.
VanderKam (1999) Another good overview of before, during and after instructions for laser patients, from a clinician’s viewpoint.
Lin (1998): This study on mice suggests laser treatment might be more effective on hair in the early growth stage.
Dover (1989): This guinea pig study demonstrated whitening of hair and skin treated with a Q-switched ruby laser. Skin whitening cleared up by four months, but hair remained white at that time.
Polla (1987): This guinea pig study demonstrated that pigment in skin is a target by lasing albino and non-albino animals. Albino animals did not respond, indicating pigmented lesions can be targeted with the laser.
Other conditions treated with ruby laser
Achauer (1996): Demonstrates superior results in removal of traumatic tattooing in a male patient.
Ashinoff (1993): Demonstrates superior results in removal of traumatic tattooing in six patients.
Chang (1996): About half of 47 patients receiving three of more Q-qwitched ruby laser treatments for pigmented facial lesions had excellent results 15 months after treatment.
Chui (1999): Three patients with severe follicular disorders (disfiguring conditions that cause massive hair loss and scarring) responded well to ruby laser after medications failed.