3. Introduction
• Hair is a simple structure that is made up of Protein filaments called
Keratin which is also the primary component of finger and toe nails.
• Hair acts as a barrier to foreign particles.
• It's an important part of appearance and creates gender identity.
• Hair is the only body structure that can completely renew itself
without scarring.
• Humans develop hair follicles during fetal development, and no new
follicles are produced after birth.
• Hair color is mostly the result of pigments, which are chemical
compounds that reflect certain wavelengths of visible light.
4. • Hair shape (round or oval) and texture (curly or straight) is influenced heavily
by genes. The physical appearance of hair can be affected by nutritional status
and intentional alteration (heat curling, perms, straightening, etc.)
• In order to test hair evidence for nuclear DNA, the root must be present. The
hair may also be tested using mitochondrial DNA whether or not the root is
present.
5. Types of Hair
Lanuga Hair:
• Develops on an unborn baby
• 3 months after baby’s conception
• Fine and soft
• grows all over the body at the same rate
• Shed about 4 weeks before the baby is due to be born
Vellous Hair:
• Short, fine, downy, unpigmented hair covering most of the body except the palms and
soles of feet
• Women normally retain 55% more vellus hair than men
• Follicle doesn’t have oil glands
Terminal Hair:
• Long, thick pigmented hair found on the scalp, legs, arms & bodies of males & females
• Coarser than vellus hair & with the exception of gray hair, it is pigmented
• Produced by follicles with sebaceous glands
6.
7.
8. Hair Structure:
Hair is made up of two separate
structures
• The hair follicle: which exists below
the skin.
• The hair shaft: which is the hair that
we see.
9. HAIR FOLLICLE: the living part of the hair
• Contains the germinal matrix, which is where cells produce new hairs.
• Contains the bulb, which is the stocking-like structure that surrounds the papilla
and germinal matrix. It's fed by capillaries.
• The follicle is surrounded by an inner and outer sheath that protects and molds the
growing hair shaft.
• The inner sheath follows the hair shaft and ends just before the opening of the
sebaceous gland.
• The outer sheath continues all the way up to the sebaceous gland
10. HAIR SHAFT: the dead hair we can actually see.
• The innermost layer: This is called the medulla. Depending on the type of hair,
the medulla isn't always present.
• The middle layer: This is called the cortex, which makes up the majority of the
hair shaft. Both the medulla and the cortex contain pigmenting cells that are
responsible for giving hair color.
• The outermost layer: This is called the cuticle, which is formed by tightly
packed scales in an overlapping structure that resemble roof shingles. Many hair
conditioning products are formulated to even out the cuticle by smoothing out
its structure.
11.
12. The Growth Cycle
• The anagen phase is the active or growth phase of the hair. Most hair is
constantly growing and spends three to four years in this stage. Hair grows
around half an inch a month, and faster in the summer than in winter. In the
growth phase, or anagen phase, a full-length hair averages 18 to 30 inches. The
anagen phase is generally longer in Asians, and can last as much as 7 years with
hair being able to grow to 1 meter. The span at which the hair remains in this
stage of growth is determined by genetics. The longer the hair stays in the anagen
phase, the longer it will grow. During this phase, cells neighboring the papilla in a
germinative layer divide to produce new hair fibers and the follicle buries itself
into the dermal layer of the skin to nourish the strand. About 85%–90% of the
hairs on one's head are in the anagen phase at any given time.
13. • The catagen phase is a transitional stage, and 3% of all hairs are in this phase at
any given time. It lasts for two to three weeks. It allows the follicle to renew itself.
During this time, the hair follicle shrinks due to disintegration and the papilla
detaches and "rests," cutting the hair strand off from its nourishing blood supply.
Signals sent out by the body determine when the anagen phase ends and the catagen
phase begins.
• The telogen phase is the resting phase, which lasts for about three months and
accounts for 10% to 15% of all hair. During the telogen, the follicle remains
dormant for one to four months. In this phase, the epidermal cells lining the follicle
channel continue to grow as normal and may accumulate around the base of the hair,
temporarily anchoring it in place and preserving the hair for its natural purpose
without taxing the body's resources needed during the growth phase.
14. Hair facts
• Each human head carries roughly 100,000 hair follicles.
• Each follicle can grow many hairs during a lifetime; on average, each
grows a new hair around twenty times.
• Not all these follicles are actively growing hairs at any one time.
From the moment when it is first formed, each follicle undergoes
repeated cycles of active growth and rest. The length of the cycle
varies with the individual, and also with the part of the body on
which the hair is growing.
• The hairs on adult scalp do not grow in unison, as they do in an
unborn baby. They are out of cycle with each other. If they were not
so, everyone would go temporarily bald from time to time.
15. References
• Laura Alonso, Elaine Fuchs, (2006) “The hair cycle.”
• https://en.wikipedia.org/wiki/Human_hair_growth
• https://www.slideshare.net/DeepakUpadhyay49/heair-grouth-cycal-
and-oral-cavity-and-skin-1
