Owing to its resistance to degradation, hair is an important bio‐sample with unique properties used to study post mortem decompositional changes. The present paper is a microscopical approach to preserved human scalp hair discovered at the 18th–19th‐century archaeological site of Iași, Romania. The hair fibre alterations were assessed using optical microscopy, scanning electron microscopy, image analysis and hair histological scores. External alterations showed a statistically significant heterogeneous degradation. Image analysis results of the internal degradation of hairs were correlated to external lesions. The results consider the implication of intrinsic biological factors in the post mortem degradation of human hair preserved in graves with comparable environmental conditions.