Light penetration into skin and the subsequent temperature rise

Where does light go when it enters the skin?

Well, it’s actually quite complicated! Some of it reflects off the skin surface, some is absorbed in the melanin (basal layer), some penetrates through to the fatty tissue, while some is turned around and escapes back into the air.

The follow slideshow gives a simple explanation about where some of this light goes:

Once in the skin, some of the light energy will be absorbed by chromophores. These may be blood, melanin, water, tattoo inks or various other stuff.

If something absorbs the light energy, then, in many cases, it will generate heat energy, raising the local temperature. Here’s how this works:

Both of these presentations are simplifications of what is going on in the skin. But they give an idea of some of the processes.

Understanding these processes is important when applying lasers and IPLs units to the skin.

You can download pdf files of the above slideshows here –


I don’t mind if you use the above in your own marketing materials or blogs – just tell them where you found it please!

Ciao for now,


3 thoughts on “Light penetration into skin and the subsequent temperature rise

  1. Hi Mike. Really great presentation. You may want to discuss what causes scattering. . One thing I would like your opinion on is penetration vs spot size. I think that scattering decreases with increased spot sizes because the waves are further apart. Chris

    Christian Slavin Founder & CEO Zapatat General: 703.248.0909 Direct: 703.789.4069

    Sent from my iPad. Please excuse my inability to spel check.


    1. Hi Chris,

      Cheers. I will discuss scattering – next year! We don’t tend to think of scattering in terms of ‘waves’. We usually consider photons since scattering is actually the absorption of a photon by an atom, and the subsequent emission of a new photon – usually in a different direction. As the spot size increases the ‘effects’ of scattering changes the power distribution in the skin. Larger spot sizes allow for a deeper penetration of more of the light energy, compared with smaller spots.

      I will cover this in a new post soon….

      In the meantime, I hope you all have a good New Year. Fingers crossed 2021 is better than 2020….

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s