Permanent hair removal methods do not exist At this time, no true permanent hair removal method exists. The FDA defines permanent hair removal as follows: “…… After a series of treatments (which may include several sessions) that result in a long-term, stable reduction in the number of regrowing hairs; the number of regrowing hairs must be longer than the full hair follicle growth cycle (4-12 months, depending on the body part) The amount of regrowth must remain stable for a period longer than the full hair follicle growth cycle (4-12 months, depending on the body part). Permanent hair removal does not necessarily mean, eliminating all hair from the treated area.” Laser hair removal can be “permanent” in a sense: after a specific treatment, the laser action causes a significant reduction in the number of terminal hairs, resulting in a significant reduction in hair without affecting the actual number of hair follicles. Most of the lasers and light source hair removal devices currently in use can partially reduce hair growth and their temporary hair removal effects can last for at least 3 months. Therefore, patients should not have unrealistic expectations about the long-term results of laser hair removal. There are no long-term (more than 2 years) studies on the efficacy of laser hair removal (this article was written in late 2007). Current commonly used light sources and wavelengths for hair removal —————————————- Type of light source Wavelength (nm) —————————————- Ruby 694 Emerald 755 Semiconductor 800-810 Nd. YAG 1064 IPL 590-1200 —————————————- Hair growth mechanism (omitted) The human hair follicle growth cycle consists of 3 phases: – anagen – catagen – telogen The anagen phase in different parts of the body Percentage of hair follicles: ——————————————– Part Percentage of hair in the anagen phase ——————————————– Scalp 85% Face 56-76% Extremities 42-51% ——- ————————————- Mechanism of light hair removal ——————————————————————————– Mechanism Effect — —————————————————————————– Thermal Localized thermogenesis Mechanical Shockwave or cavitation Photochemistry Generation of toxic mediators such as pure oxygen or free radicals Selective photothermolysis Melanin as photocarrier —— ————————————————————————– Wavelengths in the 600-1100 nm range can penetrate deep into the dermis and selectively thermally damage the hair shaft, follicle epithelium and hair matrix (to reduce damage to the epidermis and epidermal (To reduce the damage to the epidermis and epidermal melanin, selective cooling of the epidermis is required at the same time). Choosing the right wavelength, pulse width and energy density is important to optimize the hair removal effect and minimize potential side effects. If the pulse width is too long, thermal damage to the surrounding tissues may occur, thus leaving permanent scars. The normal mode ruby laser used for hair removal has a penetration depth of only about 2 mm (the depth of the hair follicle convexity is below 2 mm) and is therefore not ideal. There are several factors that must be taken into account when selecting the treatment parameters: – The hair growth cycle needs to be taken into account when determining the treatment frequency, traditionally the anagen hair (when there is more melanin in the hair) is the main target of treatment. However, there is disagreement as to whether the hair growth cycle actually has an effect on the effectiveness of light hair removal. – In order to limit the extent of thermal damage, the pulse width must be shorter or equal to the thermal relaxation time of the hair follicle (thicker follicles have shorter thermal relaxation times than fine follicles). The thermal relaxation time of human hair follicles ranges from 10-50ms. – The pulse width of the Q-switched laser is at the ns level and the thermal damage range is extremely small (limited to individual pigment cells within the hair follicle), therefore it is not suitable for hair removal. – Hair root depth (related to wavelength, spot size and energy), hair color (related to melanin content), are also factors to be considered when selecting parameters. Prior to treatment, patients must be informed of potential side effects. The main potential side effects include: hyperpigmentation, pigment loss, erythema, edema, scarring, pain, bubbles, etc. Treatment interval (omitted) Which cycle stage of hair is most suitable for treatment? Which elements of the hair follicular unit should be used as the target of action? There is still controversy about these questions. There is no definitive conclusion about the optimal treatment interval. In general, the authors recommend an interval of 6-8 weeks, which varies depending on the treatment site. Number of treatments (omitted) There is no formal recommendation on the optimal number of treatments, and studies are limited. The reason for this may be that the number of treatments involves a variety of factors such as individual hair growth characteristics, body location, and laser type. Although there is disagreement, most authors agree that multiple treatments are usually required to achieve satisfactory results, regardless of the type of laser used (only a few studies have shown no advantage of multiple treatments over a single treatment). The European Society of Laser Dermatology guidelines recommend 3-8 treatments. The authors recommend that for initial hair removal, 3-5 treatments be given; thereafter, most patients will require maintenance treatments every 6-12 months. Pre-treatment preparation There are few guidelines regarding patient preparation prior to photo-hair removal. It is usually recommended that: – Topical sunscreen or avoidance of sunlight is consistently recommended prior to surgery (as melanin is the primary color carrier for photo-hair removal). – For those with dark skin, a depigmenting cream such as hydroquinone may be recommended. – The area to be prepared for light hair removal should be culled (or otherwise) from the surface hair to avoid absorption of light energy by melanin in the hair shaft (thus diminishing the amount of energy reaching the dermal hair follicle). Traditionally, most colleagues recommend that patients do not use mechanical hair removal (plucking or waxing) prior to the procedure, as the use of these plucking methods prior to the procedure may affect the results of the light hair removal. …… In conclusion, there is conflicting evidence regarding which pre-procedure pre-treatment methods help to obtain the best results of photo-hair removal. The European Society of Laser Dermatology guidelines recommend avoiding traditional hair removal methods such as plucking, waxing, or spot hair removal prior to light hair removal because light hair removal requires hair-drying melanin to be effective; the guidelines also suggest that pre-procedure preparation can be done by clipping, culling, or using hair removal creams. The authors recommend that patients avoid plucking or waxing prior to surgery; they also recommend that patients cut or remove surface hair prior to surgery to reduce light energy loss. Recommendations for sun protection before and after treatment Persistent erythema and pigment changes are the most common complications after laser treatment. Skin inflammation is a common cause of hyperpigmentation, and post-inflammatory hyperpigmentation is more common in darker skin types. There are few controlled group studies specifically on the relationship between preoperative and postoperative sun exposure and the chance of complications from laser treatment. Therefore, sun protection recommendations have been made primarily on an empirical basis. The authors recommend that sun exposure be avoided before and for 6 weeks after laser treatment. Contraindicated sites Overall, photo-hair removal is a very safe and effective treatment; however, in some cases, the risks outweigh the benefits. It is important to note that there have been several reported cases of hair growth stimulation with photo-hair removal treatments. Special care must be taken when performing photo-hair removal treatments on the periocular area and patients must be protected (wearing an eye shield). Other than the periocular area, the authors did not see any other contraindicated treatment areas.