As the largest organ of the body, the skin is a common site of disease. Serving as the body's interface with the environment, the skin is vulnerable to an array of infectious diseases that occur throughout life. Bacteria, viruses and fungi cause numerous types of skin diseases that range in severity from mild to potentially life threatening. Additionally, the skin is a common site for abnormal immune system activity, which causes several types of chronic skin diseases.
Viruses
Several types of viral infections cause skin lesions. Herpes simplex viruses 1 and 2 cause cold sores and genital herpes, which are characterized by repetitive blister-like skin lesions. The closely related varicella zoster virus causes chickenpox and shingles. Other skin diseases caused by viruses include fifth disease; roseola; measles; German measles; and hand, foot and mouth disease, notes the patient information website DermNet NZ.
Bacteria
Bacterial infections cause a variety of the skin diseases. Folliculitis is a superficial bacterial infection of the hair follicles, characterized by discrete pus-filled, red bumps surrounding the hair. Carbuncles and furuncles, more commonly known as boils, represent deep bacterial infections of the hair follicles that form red, painful, pus-filled abscesses under the skin. The Cleveland Clinic reports that the bacterium Staphylococcus aureus is the most frequent cause of furunculosis and carbunculosis.
Erysipelas and cellulitis are common, skin diseases characterized by localized areas of skin redness and tenderness. Erysipelas, commonly called St. Anthony's fire, represents a bacterial infection of the superficial layers of the skin, typically occurring on the face and legs, notes Dr. Daniel Stulberg in a 2002 article published by "American Family Physician." Cellulitis is a deeper skin infection that is usually precipitated by a wound. Uncommonly, cellulitis spreads to the tissues underlying the skin, causing a the potentially life-threatening condition necrotizing faciitis.
Fungi
The American Academy of Dermatology notes several common fungal skin diseases, including athlete's foot or tinea pedis; jock itch or tinea cruris; ringworm or tinea corporis; and scalp ringworm or tinea capitis. Fungal skin diseases are directly and indirectly contagious. The infecting fungi commonly live in warm, moist environments, which serve as reservoirs for these infections.
Immune Reactions
Immune system reactions can cause chronic inflammation, resulting in a variety of skin diseases. An abnormal reaction of the T cells of the immune system against the skin causes the disease psoriasis, reports the American Academy of Dermatology's website PsoriasisNet. The accelerated rate of skin cell replication leads to itchy, painful areas of skin buildup.
Misguided immune system attacks on the hair follicles causes the skin disease alopecia areata. People with this disease experience periodic episodes of hair loss during disease flare-ups, explains the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Alopecia areata can affect any hair-bearing skin surface.
