Pain is often associated with laser/IPL treatments, particularly with hair removal. Why? Where does this pain come from and how can we minimise it?
An understanding of the nerve receptors in the skin is important to answer these questions. From the figure below, we can see that the ‘thermal’ receptors are located just below the epidermis – very close to the basal layer where the melanocytes live.
We can also see that the pain receptors can be found in the epidermis, and also in the upper dermis. When light energy is launched into the skin, the melanin granules absorb a significant portion of that energy (if the energy is between 400 and around 1200 nm).
As a consequence, heat is generated in the epidermis, and it stimulates a response in the pain nerve endings. This is the thermal pain felt during such treatments. The more melanin in the epidermis, the more pain may be felt.
This is the main reason for pain during laser/IPL treatments. It is a direct consequence of the locality of the nerve endings in and below the epidermal layer. The speed at which the heat energy conducts from the epidermis depends on its thickness. Darker skin will have more melanin in it, and so will conduct (lose heat) more slowly than lighter skin. Hence, darker-skinned individuals will likely feel more pain than a lighter-skinned person, for exactly the same light energy input.
For this reason, the concept of ‘pre-cooling’ is absolutely critical in reducing the pain sensations felt during treatments. By reducing the temperature of the epidermal layer before delivering any light energy, any subsequent heating will induce a lower peak temperature, thereby minimising the pain felt.
We covered this topic in one of our previous blog posts. We cannot stress highly enough the importance of pre-cooling. Not only does it reduce the pain during treatments, but it will also reduce the likelihood of unwanted tissue damage in that region of the skin.
The main purpose of many light-based therapies is to induce some sort of change in the target using light and heat. Pre-cooling will help to reduce pain and tissue damage in the upper portion of the skin through direct cooling of the epidermis. But, the intended heating of the target tissues will also result in some unwanted heat energy in the skin. This must also be addressed properly.
Post-treatment cooling is also important. As the heat energy conducts throughout the dermis, some of it will reach the temperature/pain nerve endings – after the initial heating from the epidermal layer. This must also be mitigated by skin surface cooling. Applying ice-packs or similar will help to suck the heat energy out of the skin rapidly. Air is a poor heat conductor, so water-based cooling should always be used to maximise the cooling effects (water conducts heat about four times more efficiently than air!).
Applying a water-based gel to the skin surface prior to treatments is a good idea. The water in the gel will help to remove heat from the skin rapidly. This is simple thermodynamics (look up the ‘Zeroth Law of Thermodynamics’ if you’d like to learn more about this)!
Pain control is important since many patients/clients cannot bear it. Thermal pain can be reduced significantly using cooling, especially ice-packs etc. Not only will your customers appreciate it, they will also benefit from better outcomes.
Hope this helps,
Mike and PA.