Usually not, provided that you consider as a normal situation a hill baby laying in bed at home. However, there may be some situations affected by external factors. In particular, Thermofocus should not be used on a person directly exposed to the sun, to sources of heat (a radiator or a chimney) or cold (outside during in winter, air conditioning) or again on a person that is training sport or it has just finished it (in fact, while walking, the forehead get colder because of the surrounding air).