A woman reports her hair was cut during an assault six weeks ago. Examination of a recovered hair shows bleached colour for the terminal 5 cm and natural pigmentation from the root end proximally. Assuming average scalp hair growth, this finding:

• A Is uninformative, because bleaching diffuses uniformly along the shaft
• B Refutes the stated timing, since scalp hair grows about 3 cm per month
• C Supports the stated timing, since scalp hair grows about 1 cm per month ✓
• D Proves the hair was cut within the preceding week

Explanation

Scalp hair grows at roughly 1 cm per month, so about 5 cm of new unpigmented regrowth below a bleach line corresponds to approximately five months since bleaching, consistent with a cut weeks earlier leaving the old bleached tip. Growth of 3 cm per month is far above physiological rates. Bleaching does not migrate down the shaft, and the 5 cm of differential colouration contradicts a cut within one week.

Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 7th ed.

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