Hair Growth  Human hair diameter ranges from µm  Coarse hairs grow slower & fall out less frequently than fine hairs  Head hair grows about 1 cm / month Replaced about every 3-5 yrs with new hair Replaced about every 3-5 yrs with new hair  Three stages of hair growth: Anagen phase Anagen phase Catagen phase Catagen phase Telogen phase Telogen phase

Stages of Hair Growth  Anagen phase Period of active growth Period of active growth Lasts up to 5 years Lasts up to 5 years Includes 80-90% of hair follicles Includes 80-90% of hair follicles  Catagen phase Hair is not growing; resting phase Hair is not growing; resting phase Lasts about 3 weeks Lasts about 3 weeks  Telogen phase Follicle is ready to push out the mature hair Follicle is ready to push out the mature hair Lasts 2-6 weeks Lasts 2-6 weeks Includes 8-10% of hair follicles Includes 8-10% of hair follicles

Stages of Hair Growth

Hair Root  Important in classifying hair  Telogenic human hair have bulblike root shape & lack pigment granules  Anagenic human hair may have follicular tissue still attached, look stretched, & have pigment granules present  Animal hair roots are generally spade-shaped

Hair Root Human roots look different based on whether they have been forcibly removed or they are telogen hairs that have fallen out Fallen out Forcibly removed

Mature Hair  Should have bulb-shaped base  Length of shaft varies Some cut more frequently than others Some cut more frequently than others  Tip of shaft will taper to a point Recently cut hair is squared off at tip Recently cut hair is squared off at tip ○ Becomes round after about 2-3 weeks  Split ends are result of dryness due to abuse Lack of conditioning Lack of conditioning Harsh chemicals Harsh chemicals Heat from flat irons, blow dryers, etc Heat from flat irons, blow dryers, etc

Hair at the Crime Scene  Crime scene hair considered trace evidence Can be used to backup other circumstantial evidence Can be used to backup other circumstantial evidence Investigator must determine species first Investigator must determine species first The more hair samples an investigator examines, the better The more hair samples an investigator examines, the better  Hair can be valuable evidence because It has wide range of class characteristics It has wide range of class characteristics Is persistent Is persistent Resists degradation Resists degradation Commonly found at crime scenes Commonly found at crime scenes

Hair Comparison  Investigator may associate unknown hair with an individual by comparing characteristics: Color Color Length Length Diameter Diameter Scale types Scale types Presence/Absence of medulla Presence/Absence of medulla o Medulla type, pattern & index Distribution, shape & color of pigment granules Distribution, shape & color of pigment granules  Dyed hair has color in cuticle & cortex Bleaching removes pigment & gives yellow tint Bleaching removes pigment & gives yellow tint

Hair Comparison  More characteristics that are similar, the greater degree of probability  A single significant difference between unknown (questioned) & known (exemplar) hair strongly suggests separate sources Example: hair found on victim is long, black, round cross section with continuous medulla while suspect has long, black hair with round cross section but no medulla Example: hair found on victim is long, black, round cross section with continuous medulla while suspect has long, black hair with round cross section but no medulla

Hair Comparison  Hair evidence cannot be used to determine age or sex of individual  From hair, one can determine: If the source is human or animal If the source is human or animal Race Race Sometimes Sometimes Location on the source’s body Location on the source’s body Whether the hair was forcibly removed Whether the hair was forcibly removed If the hair has been treated with chemicals If the hair has been treated with chemicals If drugs have been ingested If drugs have been ingested

DNA from Hair  If hair has been forcibly removed, some follicular tissue containing DNA may be attached Hair root contains nuclear DNA Hair root contains nuclear DNA  Hair shaft may contain mitochondrial DNA Can be typed by comparing relatives if no DNA from the body is available Can be typed by comparing relatives if no DNA from the body is available Process is more difficult & more costly than using nuclear DNA Process is more difficult & more costly than using nuclear DNA

Collection of Hair  Questioned hairs must be accompanied by an adequate number of control samples From victim From victim From possible suspects From possible suspects From others who may have deposited hair at the scene From others who may have deposited hair at the scene  Control sample 50 full-length hairs from all areas of scalp 50 full-length hairs from all areas of scalp 24 full-length pubic hairs 24 full-length pubic hairs

Hair Toxicology  Advantages: Easy to collect & store Easy to collect & store Is externally available Is externally available Can provide information on the individual’s history of drug use or evidence of poisoning Can provide information on the individual’s history of drug use or evidence of poisoning  Collections must be taken from different locations on the body to get accurate timeline  Backs up standard blood & urine tests Drugs typically gone from blood a few hours after use Drugs typically gone from blood a few hours after use Since hair grows about 1 cm / month, drug use can be traced over longer period of time Since hair grows about 1 cm / month, drug use can be traced over longer period of time  Must be careful to rule out false positives

Hair Toxicology  Napoleon died in exile in 1821  By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic  Others suggest that it was vapors from the dyes in the wallpaper that killed him

Hair Follicle Drug Test

Hair Analysis Goes Wrong