External contamination
Definition
The presence of a drug or substance on the outer surface of the hair shaft from environmental exposure rather than systemic ingestion. Distinguished from true incorporation by washing protocols, the presence of parent drug without metabolites, and uniform distribution along the shaft rather than a tapering gradient.
Related terms
- Anagen phase
- The actively growing phase of the hair follicle, during which the keratinocyte is in contact with the dermal papilla capillary and incorporates...
- Hair shaft cortex
- The main structural layer of the hair shaft, composed of tightly packed keratin filaments. It contains the melanin granules responsible for hair...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- Segmental hair analysis
- The practice of cutting a hair strand into consecutive segments (typically 1 cm each) and analysing each segment separately. Because hair grows...
- Short tandem repeat (STR)
- Short repetitive DNA sequences scattered throughout the genome, with the number of repeats varying between individuals at each locus. DNA profiling compares...
Explained in
- Hair as a Source of DNA and Toxicological InformationThe presence of a drug or substance on the outer surface of the hair shaft from environmental exposure rather than systemic ingestion. Distinguished from true...