Acne vulgaris is an inflammatory disease of the skin glands and hair follicles that appears as comedones, pustules, nodules, and nodular lesions. This disorder, which tends to run in families, affects nearly 85% of adolescents with a westernized lifestyle, although lesions can appear as early as age 8. Acne affects boys more commonly and more severely; however, it typically occurs in girls at an earlier age and tends to affect them for a longer time, sometimes into adulthood. With treatment, the prognosis is good.

Basal cell carcinoma, also known as basal cell epithelioma, is a slow-growing, destructive skin tumor that usually occurs in people older than age 40. Forty to fifty percent of Americans age 65 or older will have either basal cell or squamous cell carcinoma at least once during their lifetime. It’s most prevalent in blond, fair-skinned males, and it’s the most common malignant tumor that affects whites. The two major types of basal cell carcinoma are noduloulcerative and superficial.

Prolonged sun exposure is the most common cause of basal cell carcinoma. Indeed, 90% of tumors occur on sun-exposed areas of the body. Arsenic ingestion, radiation exposure (including tanning beds), burns, immunosuppression and, rarely, vaccinations are other possible causes.

Although the pathogenesis is uncertain, some experts hypothesize that basal cell carcinoma develops when undifferentiated basal cells become carcinomatous instead of differentiating into sweat glands, sebum, and hair.

A major burn is a devastating injury, requiring painful treatment and a long period of rehabilitation. Burns can be fatal, permanently disfiguring, and incapacitating, both emotionally and physically.

Thermal burns, the most common type, typically result from residential fires, motor vehicle accidents, misused matches or lighters (such as a child playing with matches), improperly stored gasoline, space heater or electrical malfunctions, and arson. Other causes include improper handling of firecrackers, scalding accidents, and kitchen accidents (such as a child touching a hot stove).

Chemical burns result from the contact, ingestion, inhalation, or injection of acids, alkali, or vesicants. Electrical burns commonly occur after contact with faulty electrical wiring or high-voltage power lines, or when electric cords are chewed (by young children).

Radiation burns are caused by ionizing radiation and include sunburn and radiotherapy burns. Friction, or abrasion, burns happen when the skin is rubbed harshly against a coarse surface.

Burn severity is classified by depth of injury.

An infection of the dermis or subcutaneous layer of the skin, cellulitis may follow damage to the skin, such as with a bite or a wound. If treated in a timely manner, the prognosis is usually good. If the cellulitis spreads, however, fever, erythema, and lymphangitis may occur, particularly in patients with other contributing health factors, such as diabetes, immunodeficiency, impaired circulation, or neuropathy.

Dermatitis is characterized by inflammation of the skin and may be acute or chronic. It occurs in several forms, including contact, seborrheic, nummular, exfoliative, and stasis dermatitis.

Atopic dermatitis (discussed here), also commonly referred to as atopic or infantile eczema or Besnier’s prurigo, is a chronic inflammatory response typically associated with other atopic diseases, such as bronchial asthma, allergic rhinitis, and chronic urticaria. It usually develops in infants and toddlers between ages 6 months and 2 years, commonly in those with strong family histories of atopic disease. These children typically acquire other atopic disorders as they grow older. In most cases, this form of dermatitis subsides spontaneously by age 3 and remains in remission until prepuberty (ages 10 to 12), when it flares up again. The disorder affects about 9 out of every 1,000 people.

Atopic dermatitis is exacerbated by certain irritants, infections (commonly Staphylococcus aureus), and allergens. Common allergens include pollen, wool, silk, fur, ointment, detergent, perfume, and certain foods, particularly wheat, milk, and eggs. Flare-ups may also occur in response to temperature extremes, humidity, sweating, and stress.

Herpes zoster, also called shingles, is an acute, unilateral and segmental inflammation of the dorsal root ganglia and is caused by the varicella-zoster virus (herpesvirus). It produces localized vesicular skin lesions confined to a dermatome, which may produce severe neuralgic pain in the areas bordering the inflamed nerve root ganglia.

The infection is found primarily in adults ages 50 to 70, and the prognosis is usually good, with most patients recovering completely, unless the infection spreads to the brain.

Herpes zoster is more severe in the immunocompromised patient but seldom is fatal. Patients who have received a bone marrow transplant are especially at risk for the infection.

Although the process is unclear, the disease seems to erupt when the virus reactivates after dormancy in the cerebral ganglia (extramedullary ganglia of the cranial nerves) or the ganglia of posterior nerve roots. The virus then may multiply as it reactivates, but antibodies remaining from the initial infection may neutralize it. Without opposition, however, the virus continues to multiply in the ganglia, destroys neurons, and spreads down the sensory nerves to the skin.

Herpes zoster is contagious until all the blisters are crusted over, but only for individuals who haven’t previously had chickenpox.