Permanent hair removal with the use of laser or intense pulsed light devices is a technique that evolved greatly since its introduction in the late 1980s and its approval by the FDA in 1996. Nowadays, such devices are widely used in dermatology and aesthetic medicine practices with an increased demand for permanent hair removal procedures. With the development of longer wavelength laser devices it is now possible to treat all skin types safely. 
Table of Contents
What does permanent hair removal mean?
Laser or IPL hair removal includes two different concepts:
- Temporary hair loss
- Permanent hair reduction
Temporary hair loss is defined as a delay in hair regrowth that can last up to 3 months, depending upon what phase of the hair follicle cycle the treated hair is.
Conversely, permanent hair reduction is defined as a significant reduction in the number of hair following an hair removal treatment and that is stable for longer than a full hair follicle cycle (4-12 months).
Laser or IPL hair removal causes an initial complete and temporary hair loss, up to 3 months following the treatment, and a subsequent partial permanent hair reduction. Thus, the treatment is long term effective in reducing the total number of hair and concurrently the hair left become thinner, lighter and grow more slowly.
The hair growth cycle or hair life cycle
The hair growth cycle is divided into 3 phases:
- Anagen phase, or active hair growth phase
- Catagen phase, or transitional regression phase
- Telogen phase, or resting phase (also known as shedding phase)
During the anagen phase, the cells in the root part of the hair divide rapidly, leading to hair shaft growth. During this phase, the amount of melanin in the bulb, which is already greater than the concentration in the skin, is increased further.
Catagen phase is a short transitional phase during which the hair detaches from the lower structures of the papilla which in turn enters a shrinking process stopping melanin production and starting apoptosis (programmed cell death) of the follicular melanocytes, reaching 1/6th of its original size when compared to the anagen phase. During this phase, the hair strand’s blood supply is cut off due to its detachment from the papilla and even though it is not growing anymore, its apparent length increases due to being pushed toward the surface of the skin.
Lastly, the telogen phase or resting phase sees an almost completely inactive hair follicle and a dead fully keratinized hair still attached to the body. Towards the end of this phase, the hair detaches completely from the skin and falls, while the follicle restarts its cycle entering the anagen phase.
The duration of all these phases is variable and influenced by many variables such as genetics, the region of the body and environmental factors. In general, anagen phase lasts 3-6 months for body hair versus 3-7 years for scalp hair. Catagen phase lasts between 10 days and 3 months. Lastly, telogen phase lasts about 3 months.
All these phases are not synchronized, reason why we don’t get temporary bald or hairless in our lifetime: at each moment, about 80-90% of hair are in the anagen or active growth phase, 1-2% are in the catagen or regression phase and about 10-15% are in the telogen or resting phase.
How does permanent laser or intense pulsed light (IPL) hair removal work? Selective photothermolysis
Permanent hair removal with the use of laser or IPL technologies works due to the selective photothermolysis principle. This means that the devices are calibrated on the wavelength that is selectively absorbed by the hair, which will consequently absorb the light emission transforming it into thermal energy causing thermal damage to the treated structures. The selectivity of the wavelength is such that there is no generalized damage to all neighboring structures in the treated area, but only to the specific targets, which in this case are the hair and more precisely the melanin within the hair. For this reason, laser or IPL devices are effective only in treating hair in their anagen phase, when the hair follicle is active and the melanin concentration in it is greater. For the same reason, it is not possible to treat all hair at the same time and several sessions (3-8) might be needed to achieve the desired result, a couple (4-8) weeks apart from each other, to allow the hair not in their active phase and thus not targeted by the previous treatment to enter the anagen phase and be eliminated with the following one.
Differences among permanent hair removal devices
The differences among the many types of permanent hair removal devices are mainly 6:
- The wavelength of the device
- The power of the device, intended as the amount of energy emitted per time unit
- The dimension of the treated area, known as spot size, which varies between few millimeters and a couple centimeters.
- The pulse duration, which is the amount of time during which the tissue is exposed to the light energy souce
- The fluence, which is the ratio between the power and the area (spot size) upon this power is delivered
- The presence of skin cooling systems.
In general, diode laser and alexandrite laser devices are considered the most effective, followed by IPL devices and Nd:YAG laser.
Diode laser can be used safely on I-IV skin phototypes.
Alexandrite laser can be used on I-IV skin phototypes and produces better results on thin hair, when compared to diode laser, but its use is preferred on lighter complexions.
Nd:YAG laser has a greater wavelength than the previous devices, thus a lower affinity for melanin. For this reason, although less effective, it is safer for use on V-VI phototypes and is able to produce positive results. 
Intense Pulsed Light (IPL) works in a slightly different way: laser emit a single wavelength with a single beam and all the light going in the same direction; IPL devices use a broad spectrum lamp controlled by a computer, with filters placed in front of it to select the desired wavelength. Moreover, the light emitted by IPL devices goes in all directions and only with the use of reflective surfaces it can be focused in a narrow area. IPL is safer in lower skin phototypes, due to its lower skin penetration ability and can be used also on lighter hair thanks to its broad spectrum, although with less satisfactory results when compared to its use on dark hair.
Laser hair removal is indicated for the removal of excess unwanted hair, such as facial hair in women, or for the cosmetic removal of hair which can be due to many personal reasons. Moreover, it is used in the treatment of hypertrichosis and hirsutism. It is used as a medical treatment for chronic infections such as hidradenitis suppurativa, pseudofolliculitis and folliculitis. Lastly, it is also used to remove hair from skin flaps for reconstruction purposes, when the donor area has hair which can interfere with the functionality or aesthetics of the recipient area.
Although there is no minimum age indication for this treatment, it is generally not advised under 15 years of age. Due to its mechanism of action, it is also not advised for elderly patients, with white hair, as those have no melanin in it, thus can’t absorb the energy emitted by the laser or IPL devices.
It is also contraindicated or caution is advised for:
- Patients with photoaggravated skin disorders and autoimmune disorders, such as Systemic Lupus Erythematosus (SLE)
- Patients with active infections or wounds on the area needing treatment, like herpes or staphylococci infections
- Patients with keloids or keloid tendencies
- Patients with psoriasis and vitiligo, due to the risk of developing the Koebner phenomenon.
- Patients using photosensitizing medications
- Pregnant women, although there is no evidence of any risk
- Patients using oral isotretinoin (general consensus suggests waiting 6 months to 1 year after discontinuing the drug)
- Areas with hyperpigmented lesions or tattoos
Before the treatment
Before the hair removal treatment with laser or IPL devices, sun exposure should be avoided as the skin should not be tanned during treatment. The use of retinoid creams must be suspended at least 2 days before the treatment. You should not wax, use an epilator or pluck your hair for at least one month before the session and the day before the treatment you should shave your hair with a razor or using a depilatory cream. Pay attention to the drugs used in the weeks and days before the treatment as many medications such as antibiotics, anti-hypertensives, anti-inflammatories are photosensitizing and increase the risk of post-treatment hyperpigmentation. Do not use bleaching products before the sessions. Avoid creams, talc, deodorants, cosmetics as the skin needs to be clean.
Before the session the doctor will perform a physical examination to determine the settings to use on the device as well as will ask questions about your medical history, medication use, etc. to evaluate any contraindication. You physician may also perform a patch test on a small hidden area of your body to test your skin’s response to the treatment as well as the efficacy and safety of the chosen device settings.
Cooling techniques might be used to avoid pain and major discomfort, such as ice packs, cooling creams, cooling sprays or ventilation systems.
After the treatment
Sun should be avoided for 6 weeks and the use of sunscreen is advised especially on unprotected areas such as the face. Ice packs can be applied to reduce erythema and edema as well as to attenuate the low pain or discomfort, which are normal following the treatment. It is best to avoid the use of creams, lotions, deodorants also on the day following the treatment. If after the session the physician should detect signs of excessive inflammation on the treated area, topical corticosteroids might be prescribed to lessen the side effects.
Complications and Side Effects
The most common side effects of laser or IPL hair removal are erythema and edema. Pain, burns, blistering and scarring are also possible. Hypo- or Hyper-pigmentation are not rare, but in the majority of cases are just temporary. Paradoxical hypertrichosis, whose cause is not yet clear, is reported in medical literature. 
How many sessions are needed for satisfactory results?
There is no general consensus among professionals regarding the number of treatments needed nor regarding the timespan between each treatment.
The number of treatments varies depending on the area to be treated, the patient’s characteristics and the device used.
As an estimate, about a 20-30% hair number reduction is achieved permanently with each treatment. Generally, 3 to 8 treatments are recommended to be performed 4 to 8 weeks apart from each other. 
How much does it cost?
In a country like Thailand, the price varies between US$ 30-170 depending on the device used, the clinic where the treatment is performed and the size of the area to be treated.
In South Korea prices start at about US$ 45, with the same variables as above.
Tips and Advices
Laser and IPL treatments are offered also by non-medical personnel, like beauticians, and in beauty salons and SPAs. The devices used in these cases have less power and lower efficacy when compared to the medical grade ones. Moreover, there won’t be any professional pre-treatment consultation, inspection of the area that needs the treatment and in general there is less guarantee of achieving satisfactory results and there is an increased risk of complications.
There are also a number of home devices sold for domestic use. These too have technical characteristics that make them far inferior to the medical grade ones. What might seem like a good saving in the beginning, might actually be a complete waste of money. 
The best time of the year to perform this treatment is in Autumn or Winter, when the skin is not tanned and there is a lower risk of sun exposure.
 Vachiramon V, Brown T, Mcmchael AJ. Patiente satisfaction and complications following laser hair removal in ethnic skin. J Drugs Dermatol. 2012;11(2):191–5.
 Gan SD, Graber EM. Laser hair removal: a review. Dermatol Surg. 2013;39(6):823–38.
 Lim SPR, Lanigan SW. A review of the adverse effects of laser hair removal. Lasers Med Sci. 006;21:121–5.
 Casey AS, Goldberg D. Guidelines for hair removal. J Cosmet Laser Ther. 2008;10(1):24–33.
 Thaysen-Petersen D, Bjerring P, Dierickx C, Nash J,Town G, Haedersdal M. A systematic review of lightbased home-use devices for hair removal and considerations on human safety. J Eur Acad Dermatol Venereol. 2012;26(5):545–53.
Almeida Issa MC, Tamura B. Lasers, Lights and Other Technologies. Springer, Cham 2018. https://doi.org/10.1007/978-3-319-16799-2