The skin is the largest organ of the body, measuring around 2 square meters and weighing approximately 5 kilograms. It has three main layers - the epidermis, dermis, and subcutaneous tissue. The epidermis is the outermost layer made up of keratinocytes that turnover every 28 days on average. Below this is the dermis containing hair follicles, sweat glands, collagen, and elastin which provide strength and elasticity. The deepest layer is the subcutaneous tissue consisting primarily of fat cells that provide insulation and cushioning. Understanding the structure and function of the skin is essential for aesthetic medicine procedures.

1. Skin and hair Anatomy
American board of Aesthetic medicine.

2. Skin structure and function.
Largest and heaviest organ in the body.
2 m square.
Weighs. 5 kg.
1-4 mm thickness.

3. Skin structure and function
Protection barrier against envoirnment. Barrier
against dehydration.
Body temperature regulation.
Vit D production.
Cutaneous sensation.

4. Skin structure and function.
Familiarity with skin structure and function is
essential for aesthetic medicine.
Basic structure, epidermis, dermis and sub
cutaneous.

5. Epidermis
Outer most layer of skin.
Cells continuously dividing at the base, nasal
cell.
Older cells pushed towards surface by newer to
surface layer, keratinocytes layer.
Keratinous layer shed.

6. Epidermis
70-1400 um thick, def 1 mm = 1000mm.
Average 200-400 um, overall.
Palm 800um.
Sole 1000-1400um.

7. Epidermis
15-20 tightly packed layers.
Mostly keratinocytes, squamous cells.
The outer keratinocytes layer is also known as
the horny layer, because the cells are tough like
an animal’s horn.
Average skin turnover 28 days.

8. Epidermis
Melanocytes
Produce melanin.
Melanin incorporated into keratinocytes.
1/10 cells in basal layer is melanocytes.
Skin color determine by activities of melanocytes not
number of melanocytes.
Langerhans cells, immune system.

9. Dermis
Thicker than epidermis.
Made of collagen and elastin.
Proteins in fibrous form.
Intertwined to produce elasticity and strength.
Elastin fibers are thinner, responsible for elasticity.
Sun exposure and aging, damage elastin, loose,
wrinkle skin.

10. Dermis
1000-2000 um thick.
Average 1000um overall.
Eyelid 600 um.
Sole 3000um or more.

11. Dermis
2 layers.
Papillary layer. Capillaries, nerve endings,
meisner’s corpuscle, for light touch.
Reticular layer, connective tissue, collagen, hair
follicle, sebaceous gland, sweat gland, nerve
endings, capillaries, pacinian corpuscles, deep
pressure.

12. Dermis
Hair
Primary function is protection.
Decrease heat loss.
Protection of scalp against sun.
Filter particles.
Protects against dust, brow and lashes.

13. Dermis
Hair
Shape of shaft determines curlyness.
Round shaft straight hair.
Oval shaft curly hair.

14. Dermis
Hair
All areas of body except palm, sole, lip and knuckles.
Shaft or body, elongated part growing from dermis to
outside skin.
Follicle root, ability for rapid replication.
New cells pushed in vertical alignment.
Cells die as moving upward, hard keratin.

15. Dermis
Hair growth 3 phases.
Anagen, growth laser hair removal.
Catagen, transition.
Telogen rest.

16. Sub cutis.
Below dermis.
Mostly fat cells.
Cushions inner organs.
Insulation.
Distribution of fat, hereditary and with diet and
physical activities.

17. Subcutis
Groups of fat cells separated by collagen fibers
partition.
Cellulite fibrous bands attached to deep fascia
insert into undersurface of skin to fat surrounding
the tethering protrude upon standing up.
Estrogen appears have an effect. Pregnancy, birth
control and nursing.

18. Aging
Natural aging, chronological aging.
Loses turbot, sub stance and form.
Muscles pulling on collagen constantly.
Degeneration of collagen and elastin fibers.
Thinning of skin, flattening of dermis and
epidermis junction, decrease thickness of
epidermis.

19. Aging
Chronological aging,
Smoking bring on earlier vasoconstriction.
Genetic factors, innate durability, Asian,
Hispanic, etc, anyone with darker skin.
Thicker skin wrinkle less.

20. Aging
Gravity.
Upon standing everything moves downward.
Upper eyelids fall.
Cheeks move downwards.
Tip of nose down to ground.
Upper lips get smaller, folds into mouth.
Lines forms at chin demarcation.
Ears get longer.

21. Aging
Photodamage
80% of aging.
Look at top of hands and feet.
Fine lines.
Coarse skin.
Uneven skin tone.

22. Classification of skin types
Fitzpatrick’s classification of skin type.
Provides indications of potential for PIH upon
dermal or epidermal injury.
Response to erythema producing dose of
ultraviolet lights.

23. Classification of skin types
Type 1: very white or freckled.
Always burns.
Type 2: White and usually burns.
Type 3: white to olive, sometimes burns.
Type4: brown and rarely burns.
Type5: dark brown and very rarely burns.
Type6 : black and never burns.

24. Classification of skin types
Treatment response determines by
Fitzpatrick skin types.
Degree of photo damage present.
Type1 to 3 can tolerate more epidermal and
dermal damage with minimal PIH.
Type 4 -5, have higher risk of PIH.