Skin Diseases, Disorders and Injuries: From Skin Cancer and Acne to Burns and Scars

The skin, the integumentary system, is prone to many diseases, disorders and injuries, from irritating but fairly harmless bacterial or fungal infections to skin cancer and severe burns, which can kill.

Skin cancer

Cancer is a broad name for diseases in which abnormal cells divide out of control, usually named for the organ or tissue where they start. The Skin Cancer Foundation reports that one in five Americans will have some form of skin cancer. Thinning of the ozone layer, and the extra ultraviolet (UV) light that results, has helped drive its rise: too much UV damages DNA, and the pigment melanin protects only partly. Because skin cancers also appear where the sun rarely reaches, other factors must play a part too. Cancers arise from accumulated DNA mutations that let cells survive and multiply when they should not, forming tumours; many tumours are benign, but cancers can metastasize, spreading to form tumours elsewhere.

• Basal cell carcinoma attacks the dividing stem cells at the base of the epidermis, the stratum basale. It is the most common of all cancers in the United States, found mostly on the sun-exposed head, neck, arms and back. UV is the main cause, but radiation, arsenic and wounds such as sores, tattoos and burns may contribute. It usually spreads along the base layer before growing up into an uneven patch, bump or scar, and responds best to early treatment: surgery, freezing (cryosurgery) or ointments.
• Squamous cell carcinoma affects the keratinocytes of the stratum spinosum, often on the scalp, ears and hands. It is the second most common skin cancer, about two in ten according to the American Cancer Society, more aggressive than basal cell carcinoma, and can metastasize if not removed; it is treated with surgery and radiation.

Squamous cell carcinoma on the nose. Photo: National Cancer Institute.

• Melanoma is the uncontrolled growth of melanocytes, the pigment cells, usually starting from a mole. It is the deadliest skin cancer because it spreads readily and can be hard to catch early. Treatment is usually surgery and immunotherapy.

Melanomas are usually large brown or black patches with uneven borders and a raised surface. Photo: National Cancer Institute/CDC.

Doctors teach the ABCDE signs of early melanoma: Asymmetry between the two halves; irregular Borders; mixed shades of brown or black Colour; a Diameter over 6 millimeters (0.24 inch); and Evolving shape. For nodular melanoma, the most serious form, some add Elevated, Firm and Growing.

Eczema and acne

Eczema is an inflammatory, allergic condition of all ages: dry, itchy, rash-like patches that may swell, flake or even bleed. Many people with it have antibodies to dust mites, though a link has not been proven. It is managed with moisturizers, corticosteroid creams and immunosuppressants.

Acne strikes skin rich in sebaceous glands, the face and back, most often at puberty, when hormones such as androgens drive the release of sebum. Too much sebum and keratin plug hair follicles; the plug is white at first and turns black as it oxidizes in the air. Infection by bacteria (Propionibacterium and Staphylococcus) brings redness and possible scarring.

How acne develops. Illustration from OpenStax, Anatomy and Physiology (CC BY 4.0).

Injuries and healing

Because it meets the world most directly, skin is often injured by sharp objects, heat, pressure or friction. Healing runs in overlapping stages: a clot stops the bleeding and becomes a scab; fibroblasts multiply and lay down collagen, forming granulation tissue, followed by new capillaries; immune cells such as macrophages clear foreign matter; and finally stem cells rebuild the epidermis.

Burns, from heat, radiation, electricity or chemicals, kill skin cells and can cause massive fluid loss, leading to dehydration, electrolyte imbalance and kidney and circulatory failure; infection is another grave danger. Patients get intravenous fluids and nutrients. Burns are graded by depth:

• First degree, epidermis only, painful and swollen but healing in a few days, like mild sunburn;
• Second degree, into the dermis, with painful blisters, healing in weeks if kept clean;
• Third degree, through the dermis, destroying tissue and nerve endings, white, red or black and needing medical care;
• Fourth degree, reaching muscle and bone. Oddly, third- and fourth-degree burns often hurt less, because the nerves are destroyed. Such burns cannot heal themselves and need removal of dead tissue and skin grafts.

The “rule of nines” estimates how much of the body a burn covers, to guide treatment. Illustration from OpenStax, Anatomy and Physiology (CC BY 4.0).

Most wounds deeper than a scratch leave a scar, fibrous collagen tissue without hair follicles or glands. Too much collagen makes a raised keloid; acne and chickenpox leave sunken scars. Constant pressure on bony areas of bedridden patients causes bedsores, which are fatal if untreated and infected, which is why hospitals turn patients every few hours. Skin stretched too fast during puberty or pregnancy forms stretch marks, and rubbing, such as from a badly fitting shoe, triggers the base layer to thicken into a callus, or a corn.

Sources

• J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble and Peter DeSaix, Anatomy and Physiology, "Diseases, Disorders, and Injuries of the Integumentary System", OpenStax (Rice University), licensed under CC BY 4.0. Changed: rewritten in hubnx's own words and shortened, the career feature left out, and photos credited to others not reproduced; the photos shown are the National Cancer Institute's and the diagrams the book's. This page is shared under the same licence.