Hair grows in a well-known cycle – anagen, catagen and telogen.
The ‘active’ growing phase is anagen – during this phase the hair follicle will begin to grow from a single stem cell. The duration of this phase depends on the body location and can range from a few weeks to several years!
However, these phases ‘overlap’ in any particular skin area. In other words, when we look at the skin, we see hairs in all phases, at all times! It is quite difficult to see which hair is in which phase. This poses problems for laser/IPL hair removal operators.
The following image shows how these phases may be arranged for hair on the legs, upper lip, eyebrows and arms. As you can see, there really is a wide variation in all phases, except catagen.
In most hairs, the catagen phase lasts for only two to three weeks. During this stage the hair shaft detaches from the root and ‘rises’ up through the follicle awards the surface. This is often referred to as the ‘transition’ phase and the hair is known as a ‘club’ hair at this time.
The telogen phase is the ‘resting’ stage where all growth activity has stopped. Hairs usually shed during this phase – typically up to around 100 per day.
Once the follicle goes back into the anagen phase, the newly growing hair will ‘push’ out the club hair and replace it.
Hair Growth Cycle – Legs
Let’s look at the growth cycle for leg hair.
Generally, around 20% of leg hair is in the anagen phase at any one time. This leaves the remaining 80% in catagen and telogen phases – mostly in telogen.
When looking into the ‘over-lapping’ nature of the growth cycle, it becomes clear that the ‘best’ time to carry out any light-based treatment – laser or IPL – should be chosen to coincide with the anagen phase of the cycle.
In other words, treatments should be repeated according to the anagen phase of the cycle. For legs, this is every 16 weeks! By doing this you ensure that you have the maximum number of active, anagen, follicles to target. Carrying out treatments before this time is pointless and wasteful. It will result in too many treatments with little gain, and unhappy patients!
How often do you go for a haircut? Most people leave around four to eight weeks between haircuts. Why? Because of the time it takes to ‘grow back’! There’s no point going any sooner because there won’t be enough growth. Well, it’s the same for laser/IPL treatments.
So, what about other body areas?
According to the anagen phases of hair across the body, here are our recommended treatment times:
| Area | Time between sessions |
| Eyebrows | 6 – 8 weeks |
| Arms | 13 weeks |
| Upper lip | 16 weeks |
| Under-arms | 16 weeks |
| Bikini | 6 months |
This is quite surprising, especially as we’re told to leave “six weeks’ between treatments. But this is wrong! The timings are set by the hair growth phase – not some arbitrary time!!
We will discuss this topic more fully in our upcoming eBook, which will be available soon – click here for more info.
Hope this helps,
Mike.
Mike Murphy's Blog 
I don’t understand your theory. If you have laser treatment and it is only effective for anagen stage hairs – which you say for legs is 20%. The Reason you should repeat the laser treatment again in say two weeks is to target another 20% of hairs in anagen phase and so on – so over the course of 6-8 treatments all of the hairs should be treated at the right time. If you waited 16 weeks after the first treatment to repeat the laser treatment surely it would only be treating the first 20% of hair????
Light-based therapy can only kill hair in the anagen phase. This phase varies enormously across the body. When we treat some hair at a site, we may kill around 20% of the follies. They are then dead. They cannot regrow! Any new hair which presents later comes form follicles which were not killed in previous treatments.
So, to maximise the number of follicles we can attack, we need to wait until the maximum number of follicles are in anagen – that might be 4 weeks or 4 months! It depends on the body site.
If we treat these hairs after only 8 weeks, then on a proportion of them will be in anagen – not all of them. That’s why we need to wait longer between treatments!
Hope this helps, Mike.
Maybe in theory but not in practise:), so I don’t agree with it.
I have been doing laser hair removal for 16 years, have done thousands of procedure and have noticed if clients have longer gaps between sessions they don’t have good results and opposite.
If I would do underarms every 16weeks most clients would not have results and in between the sessions they would have a growth.
So at the beginning I do recommend every 6-8 weeks and if the progress is good then I extend the time between sessions. This work for huge amount of my clients.
So with all the respect but I have a different opinion.
Hi Joanna,
Thanks for your reply.
If you successfully destroy the follicles you will only see the new growth, not “regrowth”. Unfortunately, many people don’t destroy the follicles properly in the first place!
Of course your clients will see a growth between sessions – that is to be expected! When you kill off the anagen follicles, the remaining surviving follicles will continue in their growth cycles. Some will start to grow new hairs almost immediately, while others will take longer. This cannot be stopped – light-based treatments can only kill those follicles in the anagen phase.
So, if you treat areas too soon, you will only kill a small number of anagen follicles each time, resulting in too many repeat sessions. The biology is not determined by the technology!
From the chart, it appears possible to completely destroy all underarm follicles in just four sessions!! But, to do that, you need to leave plenty of time between those sessions. Otherwise, you will do more than actually needed.
Thanks,
Mike.
Hi sir,
really interesting post!
I have developped a lot of unwanted body hair because of a treatment with minoxidil.for hair loss
It causes all the body hair to be in the anagen phase.
I would like to do laser hair removal but i was afraid that the unwanted hair keep coming back if i keep taking the minoxidil? The laser destroy the entire bulb? because minoxidil would cause a stimuli to revive the hair if the follicle is not entirely destroyed.
Thanks
Hi, I’ve only just seen this message! My apologies for the late reply. The answer is, I honestly don’t know!! I’ve never heard of anyone in this situation. Did you go ahead with the treatment?
thanks a lot for you’re answer, indeed i keep taking the minoxidil treatment ( for hair loss). accordng to you’re knowledge does shaving unwanted vellu hair on face / body make them come back darker/ thicker?