When your gel polish is curing under the lamp, it releases heat. Some people with thinner nail plates can be more sensitive to this heat. Also, the thicker you apply your polish, the more heat it can generate.
As Builder Gel is a thicker product, many do feel more heat spikes when applying this thickly.
If it is getting too hot for you, simply remove your hands from the lamp for a few seconds to cool, then slowly pop your hand back in.