Literature on thermal comfort presents two concepts beyond a static view of perception: adaptation and alliesthesia. Both concepts are typically analyzed separately and consequences for optimal conditions when following one or the other concept are not compared. Predictions concerning preferred conditions in different seasons derived from these concepts are antithetic – while adaptation suggests warmer conditions in summer being closer to neutrality – often equated with comfort – alliesthesia suggests cooler conditions in summer leading to a higher level of pleasantness – also set synonymous with comfort. The objectives of this study were to compare both concepts and the resulting views on optimal thermal conditions experimentally. The experimental study consisted of a between-subject design with two groups of participants experiencing the same three thermal conditions (classified as cool, neutral, warm) each for 50 min in a balanced order in a field laboratory with windows to the outdoors in winter (N = 32) or in summer (N = 31). Participants evaluated their thermal perception on three dimensions: thermal sensation, thermal comfort, and thermal pleasantness at the end of each session. Indoor environmental parameters and subjects’ skin temperature were recorded. Statistical analyses with participants’ ratings as the dependent, and standard effective temperature, season and sex as independent variables showed that optimal thermal conditions varied significantly between seasons, sex, the dimension of thermal perception, and the applied statistical method. Based on the results, a new type of alliesthesia is proposed to explain such effects: seasonal alliesthesia. Adaptation and alliesthesia focus on different dimensions of thermal perception and lead to distinctive results concerning optimal thermal conditions. Future work in the area of thermal comfort needs to discuss, which dimension is appropriately considered in which context and the consequences drawn for design and operation of buildings.