A multi-level overview of the hair decomposition process.

The process of hair fibre degradation is still not well studied. The first group of decompositional alterations are those caused by an external factor - the action of other organisms or environment. The main groups degrading this biological material include microorganisms such as bacteria, Micromycetes and invertebrates. The mechanism of post-mortem root banding is not well known. It is presumed to be caused by external factors (microorganisms, staining by decaying body), but also internal factors (decomposition of the hair matrix). Other degradative changes described in the literature include the breakdown of proteins (mainly keratin - the main building block of hair), photodegradation, which occurs due to the excitation of melanin radicals and elemental composition during hair decomposition. The aim of this research is to extend and systematise the knowledge of hair decomposition, in particular regarding these degradative changes, and to identify gaps and new directions for research in this field. The publications cited in this study, along with the analyses performed, indicate that hair is a promising biological material with potential applications in various fields, including forensics, archaeology, industry, and ecology. In particular, hair can be valuable for estimating post-mortem interval (PMI), as well as for genetic studies, toxicology, and life history analysis. However, key research gaps remain, notably the lack of comprehensive studies on hair decomposition and the absence of standardized, validated methods that could be widely implemented in forensic laboratories and industry.