Do you need gel for photothermal treatments?

Water-based gel is routinely used when applying lasers and IPLs on skin conditions like vascular lesions, benign pigmented lesions and hair removal. However, some manufactueres and suppliers suggest that gel is not required. Im not really sure why!

So, what happens if you use, or don’t use, gel?


As far as I am concerned there are two reasons to use gel:

     1. to help more light enter the skin through index-matching and,

     2. to help thermal energy escape from the siin more efficiently.


Light coupling:

When light approaches the skin surface it encounters a change in refractive index and reflection (known as Fresnel reflections). A small amount of gel will help to reduce the chenge in refractive index between the air and the skin, thereby increasing the amount of light energy entering the skin.


Thermal conduction:

The dermis is full of water (around 70% of the dermis is water). Water conducts heat four times faster than air. So when heat energy within the dermis reaches the skin surface the transfer of heat slows right down. This ‘traps’ that heat energy in the skin leading to unwanted elebated temperatures. By applying a water-based gel on the surface the heat energy can easily leave the skin and warm up the gel. 


I took the following photograph after i noticed the effect of an IPL pulse on a wooden spatula. The IPL was set at 36 J/cm2 with a pulse duration of 30 milliseconds. The left side shows the burning effect of this energy on the surface of the wooden spatula when no gel had been applied. The right side of the photo shows the same energy on the same spatula but where a little cooling gel had been apllied.


The difference is stark! Just one pulse of energy on the ‘dry’ side was sufficient to cause the surface of the spatula to carbonise, while the other side (with gel) is hardly touched. This clearly demonstrates the effect of applying cooling gel. Try it for yourself on a wooden spatula and see how much of an effect it makes.

Then, just think how this works on your patients’ skin!!








3 thoughts on “Do you need gel for photothermal treatments?

  1. This was interesting… question for you Mike. If I used my Medlite QSwitched Yag Laser to do hair removal (my technician told me it works well!) would I use gel? I have a very hairy friend that is keen for me to give it a go but I have never used my tattoo removal laser for hair removal. What type of settings would I use?

    1. Hi Helena,

      Q-switched lasers are not good for hair removal – the pulsewidths are too short. Hair removal is a photothermal process, which cannot be induced by any Q-switched laser. What happens, instead, is the hairs ‘fracture’ which gives the appearance of ‘removal’. But this is short-lived since the follicles are relatively undamaged.

      Longer pulses will generate a sufficient heating time to kill the follicle, which is the main aim of this process.

      Sorry, but you won’t get far with your Medlite system on this application!

      Best wishes,

      1. Oh dear… my technical kept saying “temporary hair removal” and I was thinking that he meant it was like IPL and was hair reduction… ie some of the hair would grow back.
        What about using gel for doing collagen stimulation etc with the same laser?

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