A skin disease refers to any medical condition that affects the skin, hair or nails. These conditions can be caused by a variety of factors including genetics, environmental factors, infections and autoimmune disorders. Skin diseases can range from mild to severe and may cause symptoms such as itching, redness, scaling, rashes, bumps or lesions on the skin's surface. Some common examples of skin diseases include acne, eczema, psoriasis, dermatitis, rosacea, warts, moles and skin cancer. Treatment for these conditions may involve medications, topical treatments, light therapy or surgery depending on the severity and nature of the disease.