Subzero thermal analysis of human stratum corneum.

The thermal behaviour of human stratum corneum was studied using differential thermal analysis within the temperature range of -130 degrees C to 120 degrees C. Aside from thermal transitions at around 40 degrees C, 70 degrees C, 85 degrees C and 100 degrees C, which have been reported before, a particular transition below 0 degree C (subzero), at approx. -9 degrees C (264 K), was noticed. This transition was present in the analysis curves of dehydrated as well as hydrated stratum corneum sheets and could be distinguished from the water peak found only in hydrated stratum corneum samples. To further characterize this transition, thermal analysis was performed on stratum corneum sheets: (i) after lipid extraction, (ii) after pretreatment of propylene glycol and (iii) after pretreatment of oleic acid/propylene glycol solution. From the results, it was concluded that the subzero transition (-9 degrees C) belongs to low melting lipid components of stratum corneum.