Dermatology is the study of disorders of the skin. A dermatologist is a physician who diagnoses and treats diseases of the skin. This specialist also diagnoses and treats problems of the skin, mouth, external genitalia, and some sexually transmitted diseases. A dermatologist is knowledgeable regarding skin cancers, moles, tumors of the skin, allergic reactions to chemicals or other substances, and changes of the skin associated with aging. Dermatologists also treat cosmetic disorders of the skin such as hair loss and scars, internal disorders and diseases that affect the skin, and are qualified to perform standard surgical techniques used in the field of dermatology.