Today’s Topic: The Life Cycle of Hair

October 1, 2012

Do Now:

Sketch a hair strand, and label the three components that we

discussed last week.

Agenda

• Opening• Notes• Examination of treated hair

Life Cycle of Hair

Life Cycle of Hair

• Hair proceeds through 3 stage as it develops.–Anagen Stage – Period of growth, lasts

~1000 days.–Catagen Stage – Period where hair

finishes growing, may turn gray–Telogen Stage – Hair easily falls out

Life Cycle of Hair

• Long hair can have dead and split ends or it can break

• This happens because hair in the catagen and telogen stages becomes damaged by treatment, straightening, blow drying, etc.

• Brushing your hair removes hair in the telogen stage

Life Cycle of Hair

Why does hair turn gray?

Treated Hair

• Bleaching – Makes hair yellow by

removing pigment– Makes hair brittle by

disturbing cuticle• Dyeing– Changes color of the hair

shaft (cuticle and cortex)

Treated Hair

• If a full hair is found, you can find out how long ago the hair was treated.

• Roots will have natural color

Treated Hair

• Hair grows at ~.44 mm/day or 1.3 cm/month• Dividing the length of the natural color of the

hair by 1.3 can give a date of how long ago the hair was dyed.

Treated Hair

For example: A hair strand was found at the scene of the crime. The length of the hair was 50 cm. The naturally colored root of the hair is 5.2 cm long. Approximately how long ago was this dye job done?

Treated Hair

5.2 cm = total root length1.3 cm/month = rate of hair growth

5.2/1.3 = 4 months old

Treated Hair

• Solve: The body of a woman with bleach blond hair is found in the East River. Forensic examiners take a sample of her hair. The length of the hair is 40 cm, and the root of the hair is 3 cm. Approximately how long ago was the hair beached?

Treated Hair

Answer: A little more than two months. (2.31) Root length = 3Growth Rate = 1.3/ month3/1.3 = 2.3

Treated hair

• Solve: While investigating a crime scene, crime scene investigators find a hair strand that is approximately 49 cm long. The hair is colored purple, and the root of the hair is black. The length of the black portion of the hair is 12 cm. Approximately how long ago was this person’s hair dyed?

Treated Hair

Answer: The hair was dyed approximately 9 months ago. (9.2)

Root Length = 12 cmGrowth Rate = 1.3 cm/month12/1.3 = 9.2 months

Different types of Hair

• Hair can be split into classes based on race and species

• These are only generalities and may not apply to certain individuals of races. It is also possible that individuals can have mixed characteristics.

• Note: Race is different from ethnicity

• Race – the genetic makeup and ancestry of a person

• Ethnicity – your culture and other aspects that make up who you and your family are

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