A dermatologist is a doctor who specializes in conditions involving the skin, hair, and nails. A dermatologist can identify and treat more than 3,000 conditions. These conditions include eczema, psoriasis, and skin cancer, among many others. If anyone develops an allergic reaction to any product, it is important that a dermatologist carries out an allergy test to identify the specific ingredients that are causing the problem as an allergy is for life.