Using K-type thermocouple to measure human body temperature
These themocouples have a tiny spot weld between two thin wires to make the active sensor element, which results in a very low thermal mass. Hence they change temperature quickly, which is the same thing as reacting to temperature changes quickly. As soon as you mount them in a larger substrate or coating (eg to provide a sterile insulation, to prevent breakage, to electrically isolate) you increase the thermal mass, so you have to wait longer for stabilisation.