skin

• Skin


  The largest organ of the body, where diverse cosmetic preparations are applied
• Skin care product formulations

  • Emulsions
  • Creams
  • Gels
• Epidermis


  The outermost layer of the skin, primarily made up of Keratinocytes, Melanocytes and Dendritic cells

  
• Keratinocytes


  Cells that develop from the bottom of the epidermis and rise to the top, where they are shed as dead cells. The process is called Keratinization or cornification.
• Melanocytes


  Cells that produce melanin, which contributes to skin color and provides UV protection
• Dendritic (or Langerhans) cells

  Cells involved in the immune system of the skin, swallowing foreign material and migrating out to stimulate an immune response
• Basal cells


  Small cells found at the bottom of the epidermis, from which basal cell cancers may arise
• Stratum corneum (SC) aka horny layer

  Around 15-30 layers of dead cells arranged in a "brick and mortar" structure, containing the Natural Moisturizing Factor (NMF)
• NMF (Natural moisturizing factor)


  Blend of hygroscopic compounds in the corneocytes made up of amino acids and derivatives, urocanic acid, lactic acid, urea, citrate, sugars and minerals
• Intercellular lamellar lipids


  Complex lipid material composed of ceramides, cholesterol and fatty acids, providing water-proofing and moisture permeability
• Cornified envelope


  Made up of proteins and ceramide lipids, important for water barrier functions
• Dermis


  Consists mostly of connective tissue, responsible for the skin's strength and mechanical resistance, and involved in temperature regulation
• Fibroblasts


  Produce the intercellular substances and collagen fibers
• Collagen fibers


  Provide strength to the skin
• Elastin fibers


  Responsible for the skin's elasticity
• Damage of collagen and elastin fibers results in skin loosening, thinning and wrinkling
• Collagen is also important in skin healing
• Important facts about the epidermis


  • It has no blood vessels, thus depends on the dermis for nutrient delivery
  • The skin's strength/toughness is due to keratin
  • It maintains optimal water content by limiting water loss
  • It is an antioxidant barrier against free radicals
  • It is responsible for Vitamin D production
• Blood vessels


  Network of tiny conduits in the dermis that supply the skin with fresh blood, nutrients and oxygen, and carry away waste products
• Free nerve endings


  Sensitive to pain, temperature changes and itchiness
• Nerve fibers


  Forward information such as pain and pressure to the spinal cord and brain
• Sebaceous glands


  Small organs that secrete sebum, an oily substance that conditions the hair and skin, lubricates and protects against friction, transports antioxidants, and has antibacterial and anti-inflammatory functions
• Sweat glands


  Sweat-producing structures involved in temperature regulation by helping cool the skin through sweating
• Hair follicles


  Canals of epidermis extending into the dermis, specialized to produce hair
• Subcutaneous layer / Hypodermis


  Loose network of connective tissue and fat below the dermis, acting as a protective cushion and insulating the body
• Moisture content of the skin

  Stratum corneum = 10-30%, Epidermis and Dermis = 80%
• TEWL (Transepidermal water loss)


  The total amount of water lost from the skin due to constant passive diffusion through the epidermis, about 300-400 mL per day under normal conditions
• An increase in TEWL indicates damage and compromised barrier function, causing the skin to dry, crack and peel more easily
• Skin flora


  The type and density of resident flora varies depending on anatomic location, humidity, sebum and sweat production, and other factors, protecting the skin from pathogenic invaders
• Skin pH


  Between 4.5 - 5.5, referred to as the "acidic mantle", an increase reduces desquamation, dry/scaly skin and optimal environment for pathogens
• Skin types by color and sun exposure

  • Type I (Pale white, always burns, never tans)
  • Type II (White to light beige, burns easily, tans minimally)
  • Type III (Beige, burns moderately, tans gradually to light brown)
  • Type IV (Light brown, burns minimally, tans well to moderately brown)
  • Type V (Moderate brown, rarely burns, tans profusely to dark brown)
  • Type VI (Dark brown or black, never burns, tans profusely)
• Skin types by hydration and lipid content

  • Normal skin
  • Dry skin
  • Oily skin
  • Combination skin
  • Sensitive skin
• Skin rash


  Can be the result of a moderate condition, disorder or disease, such as an allergy, chicken pox, hives or a parasitic infection, or from serious, even life-threatening conditions
• Urticaria (Hives)


  Raised, itchy areas of skin that are a sign of an allergic reaction, caused by an inflammatory reaction and release of histamine and other inflammatory mediators
• Stinging


  A transient sensation distinct from irritation and allergy, but may be considered an irritability of sensory nerve endings
• Contact dermatitis (Atopic eczema)

  A hypersensitivity reaction in the skin leading to long-term swelling and redness, often with a family history of allergic conditions
• Phototoxic dermatitis


  Also called 'sun poisoning', generally occurs due to the reaction of skin to ultraviolet rays of the sun, or certain chemicals, vitamins, sunscreens etc.
• Photoallergic dermatitis


  Also known as a sun rash, appears as a series of small red blisters, caused by repeated exposure to the sun or ultraviolet light combined with allergens
• Phototoxic Dermatitis


  Also called 'sun poisoning', generally occurs due to the reaction of skin to the ultraviolet rays of sun, leads to hyper pigmentation of that portion of the skin that is more exposed to the sun
• Causes of Phototoxic Dermatitis

  Certain chemicals like coal tar, perfumes, plants, drugs, etc that contain photosensitizing substances, vitamin shortages, sunscreen lotions