Dermatologists and cosmetologists both primarily focus on the outward appearance of individuals. * Dermatologists are trained physicians and they treat illness and disease. On the other hand, cosmetologists offer services to improve aesthetics. * Dermatologists are doctors and specialize in treating skin, hair, nails, and mucous membranes. But cosmetologists are not doctors. Cosmetologists specialize in various beauty services including haircutting and hairstyling