In order to answer this question, it is necessary to understand the process of polymerization (solidification) of UV gel under the influence of light in a lamp.
The composition of any UV gel includes UV-curable monomers and oligomers (gel base) and one or more photoinitiators. Due to the fact that the energy of UV radiation, even the harshest range
insufficient for the polymerization of UV compositions (oligomer and monomer) due to the breaking of C = C bonds, a catalyst (accelerator) is introduced into the composition of the UV gel. A photoinitiator acts as a polymerization accelerator.
Photoinitiators are chemical compounds that generate free radicals through absorption of the energy of the UV source and the corresponding photochemical reactions. The latter cause the polymerization (hardening) reaction of the UV gel. Different manufacturers may have different photoinitiator contents. The higher the photoinitiator content, the faster the UV gel polymerizes.
At first glance, the thought comes that the higher the content of the photoinitiator in the gel, the better. But it is not so. The polymerization process is accompanied by an exothermic reaction, i.e. reaction with the release of thermal energy. And the faster the gel hardens, the more heat is generated in a shorter period of time. And accordingly, the nail plate heats up more strongly. For this reason, the heat released during gel polymerization causes a burning sensation.
Now let’s see what factors affect the burning sensation:
Photo Initiator Content
The higher its content in the gel, the stronger the burning sensation.
The more transparent the gel, the better the light spreads to the depth of the applied layer, and the faster the polymerization reaction occurs. Thus, colored gels containing pigments polymerize longer under the influence of light and do not cause such a rapid burning sensation as transparent ones.
The thickness of the applied gel layer
With an increase in the thickness of the gel layer, the volume of simultaneously polymerizable material increases, and, consequently, a greater amount of thermal energy is simultaneously released. Thus, the thicker the gel layer, the more it causes a burning sensation.
Each person has a different pain threshold. Therefore, the same amount of released thermal energy can cause different sensations in different people: from a feeling of pleasant warmth to an unbearable burning sensation.
The condition of the nail plate
As noted earlier, the nail plate does not have nerve endings, so we feel the heat transmitted through the nail plate to the nail bed. Thus, the thicker the nail plate, the better it delays the spread of thermal energy and, as a result, protects the nerve endings of the nail bed from heat exposure.