## 4 Discussion
Images, courtesy of Dr. [PERSON], were acquired using the Ray 1 (Swift Medical, Toronto, ON, Canada). wet skin area. In the case of free convection flow, the magnitude of the temperature decrease can be on the scale of 2 \({}^{\circ}\)C. However, it can be higher in areas with moving air. Therefore, evaporative heat dissipation impact measurements of the wound bed temperature significantly. The problem can be solved by allowing the wound to dry completely (which may delay the timing of the assessment) or by applying a non-permeable covering to the wound bed, which eliminates the evaporation problem [23]. However, the non-permeable covering may also affect the skin's temperature [14]. The relative humidity of air does affect heat dissipation as well. However, its effect is noticeable only for evaporative heat loss from the moist skin. Figure 1b displays the heat loss functions for various relative humidity (40, 70, and 100%) at \(T_{\infty}\) = 30 \({}^{\circ}\)C for dry skin. One can see that the curves look almost identical. However, the heat loss function in the case of moist skin (see Figure 2) depends on the relative humidity quite significantly. The high relative humidity effectively inhibits the evaporation heat loss mechanism in free convection flow. The effect is two-fold: it reduces the coefficient \(q_{0}\) (primary outcome) and effective heat transfer coefficient \(h\) (minor effect). Less effective heat dissipation results in a higher skin temperature. Our model consists of four tissue-related parameters (perfusion \(\omega_{b}\), dermis thickness \(D\), epidermis thickness \(E\), and skin wetness, \(W\)), one systemic parameter (core body temperature, \(T_{c}\)), and two environmental parameters (ambient temperature, \(T_{\infty}\), and relative air humidity, \(RH\)). The tissue-related parameters are responsible for local skin temperature variations. However, visible free moisture (either perspiration or wet wound) is an undesirable condition that must be avoided during thermographic measurements. In addition, dermis thickness is relatively consistent across body parts and individuals. Thus, we can conclude that only two parameters (perfusion \(\omega_{b}\) and epidermis thickness \(E\)) are model variables contributing to local skin temperature variations in the controlled environment of the thermographic assessment. The core body temperature, \(T_{c}\), and environmental parameters (ambient temperature, \(T_{\infty}\), and relative air humidity, \(RH\)) are responsible for the absolute value of the skin temperature. However, the relative air humidity is a significant contributor just in the case of moist skin, which, as already mentioned, is undesirable and should be avoided during the thermographic assessment. Thus, in practice, the absolute skin temperature depends on two factors: the core body temperature, \(T_{c}\), and ambient temperature, \(T_{\infty}\). However, in the absence of fever, the core body temperature, \(T_{c}\), can be considered a constant. Based on these observations, three types of local thermal abnormalities are possible: (a) increased perfusion (e.g., inflammation), (b) reduced perfusion (e.g., ischemia), and (c) epidermis thickness abnormality (callus). For example, local variations (decrease) of the skin temperature can be indicative of the epidermis thickness variations, particularly in callus-prone areas. The perfusion rate \(\omega_{b}\) can be reconstructed from the observed _Delta_ using Equation (30) and compared with physiological estimates.