Dermatology is the study of skin diseases and conditions.  A dermatologist treats disorders relating to the skin, hair and nails.  A dermatologist has completed at least one year of postdoctoral training (internship), and three or more years of intensive residency training in dermatology.  After medical school, internship and residency, a dermatologist is eligible to take the board certification examination offered by the American Board of Dermatology.