Although flow indexes were not altered by thermal stress con- sistency indexes increased significantly (Table 3). It is widely known that consistency indexes normally decrease during stor- age, indicating instability (Martin et al., 1993; Korhonen et al., 2001), but in our results the consistency index increased. It is possible that this was due to the interaction of retinyl palmitate and polyacrilamide, the vehicle polymer, as shown by an arti- fact when the decomposition products were analyzed by mass spectrometry (data not shown).