5.4 Diseases, Disorders, and Injuries of the Integumentary System

Skin Cancers

Skin cancer develops when UV radiation or other factors damage the DNA in skin cells, causing them to grow uncontrollably. Recognizing the differences between the three main types matters because they vary dramatically in how dangerous they are and how they're treated.

Types of Common Skin Cancers

• Basal cell carcinoma (BCC) is the most common skin cancer. It arises from basal cells in the stratum basale of the epidermis and typically appears on sun-exposed areas like the face, ears, scalp, and neck. BCC grows slowly and rarely metastasizes, but it can cause significant local tissue damage if left untreated.
• Squamous cell carcinoma (SCC) is the second most common skin cancer. It develops from keratinocytes (squamous cells) in the upper layers of the epidermis, again favoring sun-exposed areas like the face, ears, hands, and arms. SCC is more likely to metastasize than BCC, especially if it develops on the lips or ears.
• Melanoma is the least common of the three but by far the most dangerous. It originates from melanocytes and can appear as a new or changing mole on the skin, and less commonly in the eyes. Melanoma is aggressive because it metastasizes early. The ABCDE rule is a useful screening tool: look for Asymmetry, Border irregularity, Color variation, Diameter greater than 6 mm, and Evolving size or shape.

Characteristics of Skin Disorders

Eczema (atopic dermatitis) is a chronic inflammatory condition where the skin becomes dry, itchy, red, and cracked. Small fluid-filled bumps may form, ooze, and crust over. It commonly appears on the flexor surfaces of the elbows and knees. Eczema involves an overactive immune response and a compromised skin barrier.

Management of eczema includes:

• Moisturizers to hydrate and restore the skin barrier
• Topical corticosteroids to reduce inflammation
• Oral antihistamines to relieve itching
• Phototherapy (UV light exposure) for persistent cases
• Immunomodulators like tacrolimus and pimecrolimus to regulate the immune response

Acne is one of the most common skin conditions. It occurs when hair follicles become clogged with sebum (oil) and dead skin cells, creating an environment where bacteria thrive. This leads to various lesion types: whiteheads (closed comedones), blackheads (open comedones), papules, pustules, nodules, and cysts. Acne most often affects the face, chest, and back because these areas have the highest density of sebaceous glands.

Management of acne includes:

• Topical retinoids (tretinoin, adapalene) to unclog pores and promote cell turnover
• Benzoyl peroxide to kill bacteria
• Salicylic acid to exfoliate skin
• Topical antibiotics (clindamycin, erythromycin) to reduce bacterial infection and inflammation
• Oral isotretinoin for severe, cystic cases that don't respond to other treatments

Psoriasis is a chronic autoimmune condition in which the immune system triggers abnormally rapid skin cell turnover. Normal skin cells take about a month to mature and shed, but in psoriasis this cycle accelerates to just a few days. The result is thick, red, scaly patches called plaques, commonly found on the elbows, knees, scalp, and lower back.

Vitiligo is an autoimmune disorder in which the immune system destroys melanocytes, causing a loss of pigmentation. This produces distinct white patches on the skin. It can appear anywhere on the body and is more visually noticeable in individuals with darker skin tones.

Additional Skin Conditions

• Dermatitis is a general term for skin inflammation. Contact dermatitis is a common subtype caused by direct exposure to irritants (like harsh chemicals) or allergens (like poison ivy). The reaction produces redness, itching, and sometimes blistering at the site of contact.
• Cellulitis is a bacterial infection that spreads into the deeper layers of the dermis and subcutaneous tissue. It causes redness, swelling, warmth, and tenderness in the affected area. Cellulitis can become serious if bacteria enter the bloodstream, so it typically requires antibiotic treatment.
• Impetigo is a highly contagious superficial bacterial skin infection, most common in children. It's characterized by red sores that rupture, ooze fluid, and then form a distinctive honey-colored crust.

Burns and Skin Wound Healing

Burns are classified by the depth of tissue damage. Understanding which layers are affected helps predict healing time, pain level, and whether medical intervention is needed.

1. First-degree (superficial) burns affect only the epidermis. The skin appears red and dry, and it's painful because nerve endings in the epidermis are irritated but intact. No blisters form. A sunburn is a classic example. These typically heal within a week without scarring.

2. Second-degree (partial-thickness) burns extend through the epidermis into the dermis. The skin becomes red, blistered, and swollen, and the pain is significant because dermal nerve endings are exposed. Scalding from hot liquids is a common cause. Because the dermis still contains hair follicles and glands with epithelial cells, these burns can regenerate without grafting if they aren't too deep.

3. Third-degree (full-thickness) burns destroy the epidermis, dermis, and extend into the subcutaneous tissue. The skin appears white, charred, or leathery. Paradoxically, there is no pain at the burn site because the nerve endings have been destroyed. Causes include prolonged flame exposure and chemical burns. These burns cannot heal on their own and typically require skin grafts.

The Rule of Nines is used to estimate the percentage of body surface area (BSA) affected by burns. Each major body region is assigned a value that is a multiple of 9%: the head is 9%, each arm is 9%, each leg is 18%, the anterior trunk is 18%, the posterior trunk is 18%, and the perineum is 1%. This calculation helps determine fluid replacement needs and overall burn severity.

Wound Healing Process

When skin is injured, the body repairs itself through four overlapping stages:

1. Hemostasis begins immediately. Damaged blood vessels constrict, and platelets aggregate at the wound site. The clotting cascade activates, producing a fibrin mesh that forms a clot to stop bleeding and seal the wound.

2. Inflammatory phase follows within hours. Neutrophils arrive first to fight infection, then macrophages move in to phagocytize bacteria, dead cells, and debris. This phase causes the redness, swelling, heat, and pain you associate with inflammation.

3. Proliferative phase is the rebuilding stage. Fibroblasts produce collagen to form granulation tissue (the pink, grainy tissue you see in a healing wound). Angiogenesis restores blood supply to the area, and re-epithelialization occurs as epithelial cells migrate across the wound surface to close it.

4. Remodeling phase can last months to years. Collagen fibers are reorganized and cross-linked to increase tensile strength. The result is scar tissue, which is functional but lacks hair follicles, sweat glands, and normal pigmentation.

Complications of Wound Healing

• Skin grafts are surgical procedures that transplant healthy skin to cover areas where the skin cannot regenerate on its own, most commonly after severe burns or extensive wounds.
• Keloids are an abnormal healing response where scar tissue grows beyond the boundaries of the original wound. They form raised, firm, sometimes itchy growths and are more common in individuals with darker skin. Keloids differ from normal scars because they extend past the original wound margins and rarely regress on their own.