Dermatology is the branch of medicine mainly dealing with the skin, nails, hair and its diseases. In China, sexual transmitted diseases would be attributed to this catalog as well.  
A dermatologist treats diseases, in the widest sense, and some cosmetic problems with both medical and surgical aspects.

Which including but not limited to:

♦ Skin viral infection: Herpes, wart

♦ Skin bacterial infection: epifolliculitis, abscess 

♦ Skin fungal infection: Tinea

♦ Contact dermatitis, Allergic dermatitis, Eczema, Atopic dermatitis

♦ Urticarial, Insect bite dermatitis

♦ Cutaneous pruritus

♦ Psoriasis

♦ Acne, Roseacea, pelade

♦ Benign skin tumor, Pigmented nevus, Seborrheic keratosis

♦ Anaphylactoid purpura