The main function of the skin is to protect the body that it encloses. Anatomically and physiologically, the skin's regions differ to the extent that skin is not one organ but a combination of multiple systems. The skin has a limited range of reaction patterns, but these may express a wide range of clinical syndromes. The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) states that the morphology of the lesion and the pattern of distribution suggest the differential diagnosis. Skin lesions can be characterized as macule, papule, change in pigmentation, plaque, erythema, or eczema. The evaluating physician should consider relevant characteristics, including: Is the condition localized or generalized? Does in involve the face or spare it? Does the condition involve or spare the palms and soles? Approximately 95% of occupational skin disease involves contact dermatitis from irritation, contact allergy, or both. The remaining instances usually arise from biological, physical, mechanical, or other miscellaneous causes. The AMA Guides directs the evaluating physician to complete a detailed work description and conduct a physical examination with biopsy or patch testing as needed. Because most cases of occupational contact dermatitis involve irritants, a systematic approach to examination of the skin and use of good dermatology tests can pinpoint the diagnosis in the majority of cases.