Dermatology is the medical specialty focused on diagnosing and treating conditions of the skin, hair, and nails. It includes medical dermatology, which addresses diseases like acne, eczema, psoriasis, and skin cancer; surgical dermatology, which involves procedures such as mole removal, skin biopsies, and excisions of cancerous growths; and cosmetic dermatology. Additionally, patch testing helps identify the source of allergic reactions of the skin.