Why Does it take Multiple Sessions for Laser Hair Removal to Work?

Why is it that for laser hair removal to work multiple sessions are needed?  In this post we go through some of the science behind laser hair removal to help you understand the process.

In order to understand why so many laser sessions are required to be effective it is necessary to understand how laser treatment works and its relation to the growth cycle of hair.

woman has her underarms lasered

How Laser Hair Removal Works

Lasers work by sending a beam of light at a specified wavelength to target melanin, the dark pigment found in skin and hair. Melanin is prevalent around the hair follicle, at the base of the hair. The light is converted to hot energy, which in turn disables the follicle and causes the hair to fall out (between 1 – 2 weeks after treatment).

It is for this reason that laser hair removal works best for those with light skin and dark hair; dark skin naturally contains more melanin, making it more difficult for the light to focus on its target.

It should be noted that technology is advancing rapidly in this area and there are now some lasers that have had success with darker skin.

Laser treatment is not effective for grey, white, blond or red hair.

Growth Cycle of Hair

The hair growth cycle consists of three stages: the growth stage (known as Anagen), the end of growth stage (known as Catagen) and the resting stage (known as Telogen).

Whilst the hair is in the Anagen, active growing stage, the cells in the papilla divide to produce new hair fibres and the follicle buries itself into the dermal layer of the skin to provide nourishment for the strand. This can last anything from 1 – 4 years, and is followed by the Catagen stage.

The Catagen stage (also termed transitional stage) lasts approximately 2 weeks, during which the follicle shrinks and the papilla detaches, cutting the hair strand off from its blood supply. As the follicle shrinks it pushes the hair upwards.

During the Telogen, resting stage the follicle remains dormant, and this can last from 1 – 4 months. At some point, the follicle will begin to grow again, the hair base will break free from the root and the hair will be shed. Within a couple of weeks, the new hair will begin to emerge.

The growing, or Anagen, phase then begins the cycle again.

Close up of hair growth

Significance of the Growth Cycle to Laser Hair Removal

The growth cycle is significant because laser hair removal treatment is only effective on actively growing hair i.e. during the Anagen stage, which is also when the melanin is at its most abundant.

All hair is not in the same growing stage at the same time, so when an area is treated only a percentage of the hair follicles will be affected. Therefore, it is necessary to re-treat these follicles once they have completed their cycle and returned to the growing stage.

Growth Cycle length

The length of the growth cycle varies dependant upon a number of factors, most notably being the area of the body where it is growing. The table below shows the average hair growth cycle by body part:

Body Part



Cycle Duration


3 months

1-2 weeks

10 months


3 months

1-2 weeks

10 months


10 weeks

2-3 weeks

14 months

Upper Lip

6 weeks

2-3 weeks

5 months


3 weeks

2-3 weeks

5 months


3 months

2-3 weeks

8 months


16 weeks

2-3 weeks

10 months


24 weeks

3-6 weeks

11-12 months

It is important to understand that hair growth is determined genetically, and will vary from person to person, so the table illustrated is for guidance only and represents average timings.

The part of the body being treated will affect the length of time between treatments and how many are likely to be required.

Other Factors to Take into Account

  • Hair density – unsurprisingly, the denser the hair being treated, the more sessions will be needed
  • New growth – some hair follicles are present from birth but lie dormant. It is possible that during treatment these may be stimulated into life and grow hair that was not present prior to treatment.
  • Hair re-growth – a number of follicles may survive treatment and the hair will then re-grow.
  • Individual reaction – it is widely accepted, based on various clinical data, that it is impossible to determine in advance how effective laser hair removal will be for any individual. Sometimes even those with the “ideal” fair skin and dark hair find that laser treatment does not work for them.

Treatment Packages

Woman having laser hair removal on her face

Although it may appear to be more cost effective to opt for a pre-treatment package deal, given that determining the number of sessions required in advance is impossible, it is not a route to be advised.

We would recommend that you look for a practice offering individual treatments and one that does not try to get you to sign up for a given number from the beginning.

Click here to learn more about how to choose a laser hair removal clinic.


In a nutshell, multiple sessions are needed to achieve effective results with laser hair removal because of hair growth cycles.

Other considerations include hair density, body part, rate of re-growth and individual reaction.

For more information see: Am I a Good Candidate for Laser Hair Removal?  And How Many Treatments are needed for Laser Hair Removal


I'm a computer science graduate, have a passion for self development and created this site as a side project due to the lack of complete, understandable, helpful and truthful information about hair removal available online.