Dermatology & Skin Disorders

Dermatology & Skin Disorders

Dermatology is the branch of medical science that studies the skin, its nature, structure, functions, diseases, and treatment. The skin (integumentary system) is the largest organ of the human body, covering over 3,000 square inches and weighing 6 to 9 pounds on an average adult. A cosmetologist must understand skin histology to perform facials, select appropriate skincare products, and identify skin disorders that prohibit salon services.

Healthy skin is slightly moist, soft, flexible, possesses a fine-grained texture, and exhibits a slightly acidic pH (4.5 to 5.5).

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Histology of Skin Layers

The skin consists of two primary divisions—the epidermis and the dermis—anchored to underlying body tissues by the subcutaneous layer.

1. Epidermis (Cuticle / Scarf Skin)

The outermost, non-vascular layer of skin composed of stratified squamous epithelium. It receives nourishment through blood vessels located in the underlying dermis. The epidermis contains 5 distinct layers (strata):

1. Stratum Corneum (Horny Layer): The outer layer we see and treat. Made of scale-like, dead keratinized cells (corneocytes) that continually shed and undergo desquamation. It acts as a waterproof barrier containing lipids.
2. Stratum Lucidum (Clear Layer): A thin, clear layer of dead skin cells located directly beneath the stratum corneum. Found only on the palms of the hands and soles of the feet where skin is thickest.
3. Stratum Granulosum (Granular Layer): Consists of cells that look like distinct granules. These cells are filled with keratin protein and fatty lipids, beginning the cell death and keratinization process.
4. Stratum Spinosum (Spiny Layer): The layer where the process of cell shedding begins. Contains spiny desmosomes that join cells together and Langerhans immune cells.
5. Stratum Basale (Stratum Germinativum / Basal Layer): The deepest layer of the epidermis resting on the dermis. It undergoes continuous mitosis (cell division) to produce new epidermal cells that migrate upward. It also houses melanocytes, specialized cells that produce melanin pigment to protect against ultraviolet (UV) radiation.

2. Dermis (Derma / Corium / True Skin)

The underlying, highly vascular layer of connective tissue located beneath the epidermis. The dermis is roughly 25 times thicker than the epidermis and is divided into 2 layers:

• Papillary Layer: The outer dermal layer directly below the epidermis. Contains cone-shaped projection structures called dermal papillae. Houses tactile corpuscles (nerve endings sensitive to touch), capillary loops, and melanin deposits.
• Reticular Layer: The deeper dermal layer supplying skin with oxygen and nutrients. Contains:
  • Collagen: Fibrous protein making up 70% of the dermis, providing structural strength, form, and flex.
  • Elastin: Intertwined protein fibers providing elasticity and flexibility.
  • Sudoriferous (Sweat) Glands & Sebaceous (Oil) Glands.
  • Blood and Lymph Vessels, Hair Follicles, and Arrector Pili Muscles.

3. Subcutaneous Tissue (Hypodermis / Adipose)

The fatty tissue located below the dermis. Contains fat (adipose) cells, blood vessels, and nerves. Acts as a protective cushion, stores energy, and insulates the body against cold temperatures.

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Physiology & Functions of the Skin (SHAPE S)

The six principal functions of human skin are easily remembered using the acronym SHAPE S:

1. Sensation: Nerve endings respond to heat, cold, touch, pressure, and pain.
2. Heat Regulation: Regulates body temperature (98.6°F / 37°C) through sweat evaporation and blood vessel constriction/dilation.
3. Absorption: Absorbs topical creams, oils, and ingredient molecules through hair follicles and pore openings.
4. Protection: Shields the body from injury, pathogenic bacterial invasion, chemical irritants, and UV light.
5. Excretion: Excretes sweat, salt, and metabolic wastes through sudoriferous pores.
6. Secretion: Secretes sebum from sebaceous glands to lubricate hair and skin, forming the acidic acid mantle.

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Skin Glandular Systems

• Sudoriferous Glands (Sweat Glands): Exocrine glands that excrete sweat to cool the body. Divided into eccrine glands (all over body, open directly onto skin surface) and apocrine glands (underarms and groin, attached to hair follicles, produce odor when reacting with surface bacteria).
• Sebaceous Glands (Oil Glands): Connected to hair follicles; secrete sebum, an oily substance that keeps hair soft and prevents skin dehydration.

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Lesions, Disorders & Pathology

A lesion is a mark on the skin that may indicate injury or damage.

Primary Skin Lesions (Early Stage Changes)

• Bulla: Large fluid-filled blister greater than 0.5 cm (e.g., severe burn blister).
• Macule: Flat spot or discoloration on skin surface (e.g., freckle or liver spot).
• Papule: Small, solid raised lesion containing no fluid (e.g., pimple without pus).
• Pustule: Raised, inflamed papule containing pus (e.g., acne lesion).
• Tubercle / Tumor: Solid, elevated abnormal cell mass extending into dermis.
• Vesicle: Small clear fluid-filled blister under 0.5 cm (e.g., poison ivy blister).
• Wheal: Itchy, swollen lesion caused by insect bite or allergic hive.

Secondary Skin Lesions (Late Stage Changes)

• Crust: Dead cells formed over a wound (e.g., scab).
• Excoriation: Skin sore produced by scratching or scraping.
• Fissure: Crack in the skin penetrating into the dermis (e.g., chapped lips or cracked heels).
• Keloid: Thick hypertrophic scar resulting from excessive collagen growth.
• Scale: Dry, thin plate of epidermal flakes (e.g., excessive dandruff or psoriasis).
• Ulcer: Open lesion on skin or mucous membrane accompanied by pus and loss of skin depth.

Skin Cancer Warning Signs (ABCDE Rule)

1. Asymmetry: Two halves of mole do not match.
2. Border: Irregular, notched, or blurred edges.
3. Color: Uneven shade (brown, black, pink, blue).
4. Diameter: Larger than 6 mm (size of a pencil eraser).
5. Evolving: Changing size, shape, or color over time.

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Skin Layer Structural Comparison