Final answer:
Dermatologists diagnose skin conditions primarily through physical examination and medical history, with additional tests like biopsies as necessary. The ABCDE mnemonic is a tool used for early detection of melanoma.
Step-by-step explanation:
In dermatology, the diagnosis of skin conditions and rashes is most frequently made from a combination of a physical examination and medical history of the patient. Dermatologists may perform additional tests, such as a biopsy for a definitive diagnosis of cancerous lesions, as well as ordering blood tests or imaging studies if systemic diseases are suspected. For issues such as contact dermatitis or delayed-type hypersensitivity, the diagnosis may be based on a thorough history of exposure to potential allergens or irritants. In the case of melanoma, doctors often use the ABCDE mnemonic to help patients in the early diagnosis of this form of skin cancer.