Actinic (solar) keratosis: A skin lesion that develops in sun damaged skin. It often appears as a red, scaly patch and is considered to be an early form of squamous cell carcinoma.

Acrodermatitis enteropathica: A red, scaly rash often Involving the skin around the mouth and diaper area that results from an inherited or acquired deficiency of zinc.

Allergic contact dermatitis: A rash that results from an allergic reaction to a substance that comes in contact with the skin.

Atopic dermatitis: A rash that usually begins in children, often involving the face and skin folds of the arms and legs. It results from scratching skin that is usually dry, itchy, and very sensitive to irritating substances. It may be associated with seasonal allergies and asthma.

Bacillary angiomatosis: An infection with a specific bacteria (Bartonella quintana) most often, but not exclusively, seen in patients with AIDS. It results in the formation of multiple red papules on the skin.

Basal cell carcinoma: A type of skin cancer that arises from the skin or hair follicle and resembles the lowermost (basal) layer of the skin under the microscope. Basal call carcinoma grows slowly, may be locally destructive and rarely spreads beyond the skin. It is one of the most common forms of skin cancer and is usually seen in fair skinned individuals.

Bowen’s disease: A form of squamous cell carcinoma in-situ that may develop on non-sun-damaged skin. It can be associated with wart (human papillomavirus) infection.

Complement: Substances in the blood that are required for normal immune function and resistance against infections. An acquired or hereditary deficiency of complement factors may result in a variety of diseases, some of which may have skin manifestations.

Condyloma: A type of wart caused by infection with the human papillomavirus. Most condyloma are sexually transmitted.

Dysplastic nevus: A non-cancerous nevus that has a characteristic appearance to include variability in color, sometimes a centrally raised area and, often, indistinct borders. In some individuals and families dysplastic nevi may be a marker for an increased risk of developing melanoma.

Ichthyosis: A group of skin disorders that result from abnormal formation or multiplication of skin cells. Some forms of ichthyosis are inhereited, others may be acquired.

Kaposi’s sarcoma: A condition that is due to the abnormal proliferation of cells similar to those that line blood vessels, resulting in purple to brown papules and plaques. It usually involves the skin, but may also develop in mucous membranes and the intestinal tract. Kaposi’s sarcoma is a feature of AIDS, but may also develop in people who do not have AIDS. It is associated with a specific viral infection (human herpes virus type VIII).

Lupus (lupus erythematosus): A condition in which an immune reaction develops against normal structures in the body (an autoimmune condition). Lupus may affect any organ, but most commonly the skin, joints and kidneys. Charactistic findings may be seen on skin biopsy.

Malignant melanoma: A cancer of pigment producing cells (melanocytes) that usually begins in the skin but that may arise in other sites such as the nail unit, eye, intestinal tract or mucous membranes.

Necrobiosis lipoidica diabeticorum: A skin condition characterized by yellow-orange patches or plaques most often on the shin. It is closely associated with diabetes (about 2/3 have or will develop diabetes) and has characteristic findings on skin biopsy.

Netherton’s syndrome: An inherited disorder that combines features of a rash (ichthyosis linearis circumflexa), abnormalities of the hair and atopic or allergy symptoms.

Nevus (nevi): A non-cancerous growth of pigment producing cells (nevo-melanocytes) commonly referred to as a “mole”.

Psoriasis: An inflammatory condition of the skin that results in well defined, red scaly plaques. It often involves the elbows, knees and scalp and may be associated with abnormalities of the nails.

Psoriatic arthritis: A form of inflammatory arthritis associated with psoriasis. It often involves the joints of the fingers, but may involve any joint including those of the spine.

Pyogenic granuloma: A benign proliferation of blood vessels which is usually superficially located in the skin or mucous membranes where it presents as a nodular or polypoid, red to purple, often ulcerated lesion.  The lesions usually result from some type of external trauma such as a puncture wound.

Sarcoidosis: An inflammatory disorder that results in the formation of granulomas (collections of cells called histicytes that have characteristic features). Sarcoidosis often involves the skin, lungs and eyes.

Seborrheic keratosis: A non-cancerous growth of skin cells usually seen in people over 30. It may be tan, brown or black and usually has a “stuck-on” warty appearance.

Squamous cell carcinoma: A type of cancer that begins in squamous cells - usually-thin, flat cells that resemble cells of the middle layer of the skin. Squamous cells are found in tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts.

Squamous cell carcinoma in-situ: A form of squamous cell carcinoma that arises from, and is limited to the skin. It most often develops in heavily sun damaged skin.