How long do substances remain detectable in hair?
Written by
Leilani Ibeh
Reviewed by
Prof. William Dalton, Ph.D.The periods of exposure detection with hair tests vary considerably, because different parts of the body produce different tissues, and between different persons, growing hair at different rates. The growth of hair is approximately 1 cm per month, providing a biological timeline that enables the detection of postponement, which cannot be achieved with blood and urine tests.
Hair Growth Rate
- Average growth: 1 cm per month (range 0.7-1.5 cm)
- Faster growth shortens detection window
- Scalp location affects growth consistency
- Nutritional status impacts growth speed
Substance Binding Properties
- Lipophilic compounds bind tightly to keratin
- Water-soluble substances wash out more quickly
- Molecular weight affects retention duration
- Metabolite stability determines detectability
External Influences
- Hair porosity affects substance retention
- Chemical treatments accelerate leaching
- Environmental exposure adds contaminants
- Washing frequency impacts residue levels
Segmental analysis allows for a precise historical reconstruction. Technicians sample 1cm segments that represent monthly exposure. This will enable observations of exposure patterns, such as chronic and occasional exposure patterns. For heavy metals, deposition is cumulative across multiple segments.
Detection limits vary based on the precision of the analysis. Mass spectrometry can identify substances at the parts-per-billion level. Hormones usually require specialized LC-MS/MS testing. Always confirm your laboratory's detection limits for individual compounds.
Environmental contamination can distort timelines. Proper washing protocols remove external residues. Forensic labs differentiate between internal incorporation and external deposition using specialized solvent techniques.
Read the full article: Understanding Hair Mineral Analysis Secrets
