It is not clear how converting epidural analgesia for labour to epidural anaesthesia for emergency caesarean section affects either cutaneous vasomotor tone or mean body temperature. We hypothesised that topping up a labour epidural blocks active cutaneous vasodilation (cutaneous heat loss and skin blood flow decrease), and that as a result mean body temperature increases. Twenty women in established labour had body temperature, cutaneous heat loss and skin blood flow recorded before and after epidural top‐up for emergency caesarean section. Changes over time were analysed with repeated measures ANOVA. Mean (SD) mean body temperature was 36.8 (0.5)°C at epidural top‐up and 36.9 (0.6)°C at delivery. Between epidural top‐up and delivery, the mean (SD) rate of increase in mean body temperature was 0.5 (0.5) °C.h−1. Following epidural top‐up, chest (p < 0.001) and forearm (p = 0.004) heat loss decreased, but head (p = 0.05), thigh (p = 0.79) and calf (p = 1.00) heat loss did not change. The mean (SD) decrease in heat loss was 15 (19) % (p < 0.001). Neither arm (p = 0.06) nor thigh (p = 0.10) skin blood flow changed following epidural top‐up. Despite the lack of change in skin blood flow, the most plausible explanation for the reduction in heat loss and the increase in mean body temperature is blockade of active cutaneous vasodilation. It is possible that a similar mechanism is responsible for the hyperthermia associated with labour epidural analgesia.