One of the main roles of brown adipose tissue (BAT) is the rapid generation of heat at birth in response to cold exposure to the extra-uterine environment. This is mediated by the rapid increase in a range of neuro-endocrine stimulators within the fetal circulation which includes noradrenaline, cortisol, thyroid hormones and prolactin. The rate of decline in these factors may then start to initiate the gradual decline in BAT in a depot specific manner. This could contribute to the divergent molecular signatures of different adipose tissue depots which are dependent on whether they were either white or brown in origin. It is now established that BAT is present throughout the life cycle in humans although the challenge is to establish on a population wide basis the main factors that regulate this process. We have thus developed the use of thermal imaging in order to assess the physiological regulation of BAT and establish the critical time points at which it is lost. We have also shown in a large human cohort that the presence of BAT is more closely related to the prevailing photoperiod rather than ambient temperature. The extent to which photoperiod, as opposed to ambient temperature, is a primary regulator of BAT function remains uncertain. The prolactin receptor is necessary for normal BAT function and in the newborn sheep, direct stimulation of the prolactin receptor promotes BAT thermogenesis. Changes in maternal diet can determine the amount of BAT in the newborn, an adaptation mediated through changes in prolactin receptor abundance.