Redness in women may therefore not only indicate cardiovascular fitness, but may also be a subtle cue to fertility, as is found in females of other primate species. Redness change thresholds for the health and attractiveness tasks were not significantly different. One possible interpretation of this finding is that health and attractiveness are perceptually equivalent when they are assessed based on facial redness. Skin redness is indicative of blood oxygenation, and thus cardiovascular fitness. It is conceivable that facial redness preferences may have evolved to exploit this cue to health. Differences can arise between perceived optimal health and attractiveness in some facial parameters, such as facial adiposity but similar redness change thresholds for perceived health and attractiveness suggest that the two attributions are closely linked for colour. Facial redness may be another parameter where attractiveness is linked to underlying health. The redness discrimination task required a smaller redness change than did the health or attractiveness tasks. It is possible that these threshold differences can be attributed to differences in the degree of neural processing. The redness discrimination task requires a straightforward decision on colour intensity. Judgments on health and attractiveness are more complex and likely to require involvement from reward centres of the brain before judgments can be made. It is possible that the threshold differences found in the current study are due to an extra step in processing the health and attractiveness judgments. Other psychophysical studies on social attributions, however,Chlorothiazide have found that stimulus change thresholds for social attributions are not always higher than those for simple discrimination. For example, thresholds for voice pitch discrimination and attribution of vocal masculinity are not significantly different. It is therefore conceivable that threshold differences between stimuli discrimination tasks and social attribution tasks depend on how closely linked the social attribution is to the sensory cue. For example, threshold differences between redness discrimination and health and attractiveness judgments are likely to be smaller than the threshold differences for a cue less well associated with health and attractiveness. The current experiment used two men’s and two women’s faces to establish thresholds for facial redness in assessing health and Ceftazidime attractiveness. Whereas thresholds did not differ between these four faces, we cannot be sure that thresholds would not differ for faces that are initially very low or high in perceived health and attractiveness. For example, a face that is already very healthylooking and attractive may need a greater change in redness to increase perceived health and attractiveness. Increasing redness raised perceived health and attractiveness for each of the four faces used here, and this indicates there were no ceiling effects for perceived health and attractiveness for these four faces. Further research could determine whether or not thresholds depend on initial perceived health and attractiveness. It is important to note that facial redness is not only associated with blood oxygenation and oestrogen levels but also with emotions such as anger and embarrassment. Fluctuations in skin redness in response to such emotions are transient, however, and pass relatively quickly. Long-term preferences for facial redness are unlikely to reflect such short-term fluctuations, and more likely stem from stable long-term cues to physiology. It should be noted that the current experiment presented trial images sequentially, for a short period of time, with a visual mask presented in between.