Skin temperature: its role in thermoregulation

Abstract

This review analyses whether skin temperature represents ambient temperature and serves as a feedforward signal for the thermoregulation system, or whether it is one of the body's temperatures and provides feedback. The body is covered mostly by hairy (non-glabrous) skin, which is typically insulated from the environment (with clothes in humans and with fur in non-human mammals). Thermal signals from hairy skin represent a temperature of the insulated superficial layer of the body and provide feedback to the thermoregulation system. It is explained that this feedback is auxiliary, both negative and positive, and that it reduces the system's response time and load error. Non-hairy (glabrous) skin covers specialized heat-exchange organs (e.g. the hand), which are also used to explore the environment. In thermoregulation, these organs are primarily effectors. Their main thermosensory-related role is to assess local temperatures of objects explored; these local temperatures are feedforward signals for various behaviours. Non-hairy skin also contributes to the feedback for thermoregulation, but this contribution is limited. Autonomic (physiological) thermoregulation does not use feedforward signals. Thermoregulatory behaviours use both feedback and feedforward signals. Implications of these principles to thermopharmacology, a new approach to achieving biological effects by blocking temperature signals with drugs, are discussed.

Figure 1

Feedback and feedforward in thermoregulation. The multisensory, multieffector thermoregulation system can be described as a federation of relatively independent thermoeffector loops (Romanovsky 2007b). The three hypothetical schematics show how body temperature may be regulated within an individual thermoeffector loop. The active elements of each loop (in principal, thermoreceptors and the thermoeffector) are marked as the active system; the passive system (processes of heat transfer) is marked as heat transfer. (a) Deep body temperature is controlled via a negative (−) feedback loop. (b) Deep body temperature is controlled by the same negative feedback loop (from deep body temperature) supplemented by a feedforward signal (ambient temperature). The feedforward control signal is shown in red. (c) The same negative feedback control loop (as in panel a) is supplemented by auxiliary feedback control (from skin temperature). The auxiliary feedback (which can be negative or positive, +/−) is shown in red.

Figure 2

Two types of skin in a rat. Two images of a genetically hairless (Crl:CD‐Hrhr) rat exposed to cold are overlaid. The bottom layer is a regular (visible spectrum) photograph. The top layer is a transparent infrared thermogram. In the thermogram, temperatures from 31.0 to 37.0 °C are coded with yellow (from dark to light respectively), temperatures below 31.0 °C are coded with black, and temperatures above 37.0 °C are coded with purple. As a result, the vasoconstricted skin over the heat‐exchange organs shows as black, whereas the skin over the rest of the body is yellow. The external acoustic meatus and the skin over interscapular brown adipose tissue have higher temperatures and show as purple.