History and physical examination are adequate for diagnosing many skin lesions Description of Skin Lesions An extensive language has been developed to standardize the description of skin lesions, including Lesion type (sometimes called primary morphology) Lesion configuration (sometimes called secondary... read more 
. Some require biopsy or other testing.
Dermatologic history
Important information to obtain from history includes
Personal or family history of atopy Overview of Allergic and Atopic Disorders Allergic (including atopic) and other hypersensitivity disorders are inappropriate or exaggerated immune reactions to foreign antigens. Inappropriate immune reactions include those that are... read more (suggesting atopic dermatitis Atopic Dermatitis (Eczema) Atopic dermatitis is a chronic relapsing inflammatory skin disorder with a complex pathogenesis involving genetic susceptibility, immunologic and epidermal barrier dysfunction, and environmental... read more
)Long-term exposure to sunlight or other forms of radiation (benign and malignant skin tumors Overview of Skin Cancer Skin cancer is the most common type of cancer and commonly develops in sun-exposed areas of skin. The incidence is highest among outdoor workers, sportsmen, and sunbathers and is inversely related... read more )
Systemic disease (diabetes Infection In patients with diabetes mellitus, years of poorly controlled hyperglycemia lead to multiple, primarily vascular, complications that affect small vessels (microvascular), large vessels (macrovascular)... read more
and Candida Candidiasis (Mucocutaneous) Candidiasis is skin and mucous membrane infection with Candida species, most commonly Candida albicans. Infections can occur anywhere and are most common in skinfolds, digital... read more 
or tinea Overview of Dermatophytoses Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by... read more , hepatitis C Hepatitis C, Acute Hepatitis C is caused by an RNA virus that is often parenterally transmitted. It sometimes causes typical symptoms of viral hepatitis, including anorexia, malaise, and jaundice but may be asymptomatic... read more , and cryoglobulinemia)Sexual history (syphilis Syphilis Syphilis is caused by the spirochete Treponema pallidum and is characterized by 3 sequential symptomatic stages separated by periods of asymptomatic latent infection. Common manifestations... read more
and gonorrhea Gonorrhea Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. It typically infects epithelia of the urethra, cervix, rectum, pharynx, or conjunctivae, causing irritation or pain and purulent... read more 
)Use of drugs (Stevens-Johnson syndrome, toxic epidermal necrolysis Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) Stevens-Johnson syndrome and toxic epidermal necrolysis are severe cutaneous hypersensitivity reactions. Drugs, especially sulfa drugs, antiseizure drugs, and antibiotics, are the most common... read more
)
A negative history is as important as a positive history. The history of the particular skin lesions is also important, including time and site of initial appearance, spread, change in appearance, and triggering factors.
Dermatologic examination
Visual inspection is the central evaluation tool; many skin disorders are diagnosed by the characteristic appearance or morphology of the lesions ( see also Description of Skin Lesions Description of Skin Lesions An extensive language has been developed to standardize the description of skin lesions, including Lesion type (sometimes called primary morphology) Lesion configuration (sometimes called secondary... read more ). A full skin examination, including examination of the scalp, nails, and mucous membranes, is done to screen for skin cancers and to detect clues to the diagnosis of a widespread eruption. Magnification with a hand lens can help reveal morphologic detail. A hand-held dermatoscope with built-in lighting is particularly useful in evaluating lesions. Further information can be gathered by using diascopy or a Wood light Wood light Diagnostic tests are indicated when the cause of a skin lesion or disease is not obvious from history and physical examination alone. These include Patch testing Biopsy Scrapings Examination... read more 
.
