The light is tuned to the pigment in the hair, which turns it to heat and kills the cells at the base of the follicle that regrow it 1. Your skin pigment competes for the same light, so the darker your skin the narrower the safety margin. And only an actively growing follicle has a shaft to catch the light, so one session is never enough: a course sweeps up the follicles dormant last time.
Across the trials, hair counts settle at roughly 30 to 60% of baseline after a six-session course, survivors coming back thinner and lighter 2. A four-way underarm comparison put every device between 67 and 84% reduction at six months 3. The word the regulators allow is "permanent reduction". Home IPL devices are real but weaker: 38 to 68% on small areas over twelve weeks 4.
Three cases the physics decides for you. Dark coarse hair on light-to-medium skin is the win: alexandrite or diode, fewer sessions, low risk. Dark skin needs long-pulsed Nd:YAG, because everything else burns the skin before the follicle 5. Grey, white, blonde, or red hair has no pigment for the light to grab, so no light device touches it; that group wants electrolysis.
Screen yourself, then screen the clinic.
The arc. By session two or three the field is visibly thinner and stays smooth longer between shaves. Three to six months after the last session the count plateaus: on a well-matched area, 50 to 70% fewer terminal hairs, survivors finer 6. A year or two on you're booking the odd touch-up, and the background habit of tracking when you last shaved has closed. For women with PCOS, facial hair is one of the syndrome's most distressing symptoms, and a course paired with prescribed anti-androgen therapy lifts it measurably 7. Some hair survives and maintenance never hits zero, but the chore ends.
The fine print — when to skip it, and what people get wrong
Courses fail for the same reasons: the fluence was set too low to sell a gentler-sounding session 8; the device was wrong for the skin; or the patient showed up waxed, or stretched the sessions so far apart the cadence stopped matching the hair cycle.
Defer during pregnancy, active herpes near the site, or recent isotretinoin. Flag photosensitising drugs and any autoimmune photosensitivity. No treatment inside the bony eye rim, or straight over tattoos.
"IPL is laser": no, it's a filtered flashlamp, with a narrower safety margin on dark skin. "Works on all colours" means fine vellus hair or a bolt-on, not grey or blonde. "Home device is clinic-grade": it's capped well below clinic power on purpose 4.
- 1Anderson RR, Parrish JA (1983). Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science. link
- 2Dierickx CC (2000). Hair removal by lasers and intense pulsed light sources. Dermatologic Clinics. link
- 3Toosi P, Sadighha A, Sharifian A, Razavi GM (2006). A comparison study of the efficacy and side effects of different light sources in hair removal. Lasers in Medical Science. link
- 4Thaysen-Petersen D, Bjerring P, Dierickx C, Nash JF, Town G, Haedersdal M (2014). A systematic review of light-based home-use devices for hair removal and considerations on human safety. Journal of the European Academy of Dermatology and Venereology. link
- 5Battle EF, Hobbs LM (2004). Laser-assisted hair removal for darker skin types. Dermatologic Therapy. link
- 6Haedersdal M, Wulf HC (2006). Evidence-based review of hair removal using lasers and light sources. Journal of the European Academy of Dermatology and Venereology. link
- 7Schroeter CA, Raulin C, Thürlimann W, Reineke T, De Potter C, Neumann HA (2004). Hair removal in 40 hirsute women with an intense laser-like light source. European Journal of Dermatology. link
- 8Lanigan SW (2003). Incidence of side effects after laser hair removal. Journal of the American Academy of Dermatology. link
Laser and IPL Hair Removal
Visible thinning and slowing of regrowth from session 2–3 onward; final state at 6–12 months is markedly smoother, less-pigmented skin in the treated area, consistently noticed by others. Cochrane-level synthesis reports ~50% short-term reduction at 1–3 months and durable reduction at 6 months across alexandrite, diode, Nd:YAG, and IPL (Haedersdal and Wulf 2006).
Six to eight clinic sessions over 6–12 calendar months, each 15–90 minutes including travel; pre-session shaving and sun-exposure avoidance for 4–6 weeks before each visit. Home-device protocols are similar in calendar duration but compressed to short solo sessions. Not daily, but a real commitment for a season.
Mature literature: Cochrane-grade evidence-based review across 11 RCTs and 19 controlled trials reporting consistent ~50% long-term reduction across device categories (Haedersdal and Wulf 2006); within-class device comparisons (Toosi et al. 2006) and skin-type-stratified guidance (Battle and Hobbs 2004) well-established; mechanism (selective photothermolysis) experimentally validated since Anderson and Parrish 1983.
Long-term residual hair count plateaus at 30–60% of baseline on responsive areas with surviving hairs finer and lighter (Dierickx 2000); secondary effect on long-term skin quality through eliminating decades of shaving/waxing-induced ingrowns, folliculitis, and post-inflammatory pigmentation (Ross et al. 2002 in pseudofolliculitis barbae).
Typical in-clinic 6-session courses run $300–600 per session for small areas and $600–1,500 for large; a full-body course is commonly $3,000–6,000+. Home IPL devices run $200–500 once. Most readers will spend $500–2,000+ on the areas they actually care about, landing in the substantial range.
Real but modest reduction in chronic ingrown-hair inflammation and folliculitis, especially meaningful in pseudofolliculitis barbae populations where Nd:YAG produced sustained reduction in papule counts and patient-rated discomfort (Ross et al. 2002). Not a wellness intervention for the general user.
Quality-of-life literature in hirsutism (PCOS-driven facial hair in women) consistently shows the symptom among the highest-distress in the syndrome; treatment courses produced measurable improvements in self-image, social comfort, and mood scales (Schroeter et al. 2004). For the general user (axilla, legs, bikini), the mood effect is smaller — relief from a chore rather than a clinical lift.