How much hair is removed after each laser/IPL treatment?

This is an interesting question. It’s tricky to know precisely because it’s hard to ‘count’ the hairs…

So, I used my computer model of the anagen-catagen-telogen growth cycle to find out. This is the model I developed last year to figure our how long we should leave between treatments for the best outcomes.

To answer this question, I looked at the underarms and pubic hair. According to clinical studies, these areas have very similar cycles with 53% of all hair in the anagen phase at any one time, and 40% in the telogen phase. The duration of the anagen phase was found to be around 16 weeks, while the telogen phase lasted for about 12 weeks.

I know, from previous work, that most people are achieiving an efficiency of between 50 and 60% when applying these treatments. So, in this analysis I have assumed a ‘worst case’ scenarion of 50% efficiency.

I decided to go for a 6 week interval between treatment sessions – again, a ‘worst case’ scenario. So, these results will show the poorest of all outcomes!

The graphs above show the drop in all three phases, plus the total percentage of hairs left after each treatment, over 42 weeks (8 treatments).

The blue line shows how the percentage of anagen hairs bounces around, especially after the first four treatments. It begins at 53% then drops to 41% just prior to the second treatment, then down to 38% just before the third treatment – not much difference! This then falls to 25% just before the fourth treatment session.

In the above graph we can see the percentage reduction of all hair after each treatment session. After the first treatment we can see a total reduction (of all hair) of around 27%, followed by 21, 19, 12 and then 6%. The final treatments only remove around 3% each!

It really is a case of ‘diminishing returns’ with each tratments. There are fewer anagen follicles available each time a patient/client comes back, so each treatment attacks a smaller number of anagen follicles.


As we can see, the reduction of hair following laser/IPL treatments is not obvious. Assuming the worst possible outcomes in each treatment, we can see that the loss of hair follicles drops by around 20 to 27% for the first three sessins, then drops to around 12% and below. Just over two-thirds of the hairs (67%) are removed in the first three sessions.

But, the top graph shows that the number of anagen follicles may not change by that much over the first three or four sessions. This can be a bit irritating when treating clients/patients, but you should explain that they are seeing ‘new’ growth alongside ‘re-growth’ (from those follicles you didn’t kill previously).

I will do this analysis again using a longer gap between sessions – that should yield a more efficicient outcome. I’ll post this up soon…

Hope this helps,


P.S. Don’t forget my MasterClass coming up next month in Manchester…

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