Relative studies between hair index, hair area, and medullary index with age and sex in Thai scalp hair

- Hair index (HI), hair area (HA), and medullary index (MI) relative to age and sex differences were explored in scalp hair.
- HI and MI did not significantly differ according to age and sex.
- HA was significantly different between males and females at 50-69 years of age.
- HA significantly increased during their early twenties and then decreased gradually until ≥80 years of age.
- HA might be useful for forensic, medical, and anthropological investigations.

Human scalp hair is one of the most common trace materials found at violent crime scenes. Accordingly, scalp hair is critical evidential material in forensic investigations for identifying relations and persons, which could result in solving cases. Knowledge about micro-morphological variations of scalp hair in the Thai population, however, is scarce, and information on age changes and sex differences with respect to these traits is limited. The present study was thus undertaken to explore three micro-morphological parameters of Thai scalp hair-hair index (HI), hair area (HA), medullary index (MI)-relative to age and sex differences. Scalp hair samples were collected from 340 unrelated Thai cadavers (170 male, 170 female) of all ages, which were divided into seventeen age groups, 5-year-old interval per group beginning with 0-5 years and ending up with ≥80 years. Approximately 30 hair strands at the posterior vertex region of the scalp were cut with scissors as close to the scalp as possible. The hair samples were subsequently used to make permanent slides, and the mounted hairs were examined for microscopic cross-sectional characteristics. The authors found that the HI and MI were similar in the male and female cadavers and did not significantly differ (p > 0.05) according to age. In contrast, the HA was significantly different between the male and female cadavers at 50-69 years of age (p < 0.05). There were other differences according to age as well. That is, the HA increased abruptly during their early twenties and then decreased gradually until ≥80 years of age. Thus, Thai scalp hair shows some age and sex variations that are reflected in the HA and might be useful for forensic, medical, and anthropological investigations.