I had to think about this question for awhile because it depends on who you ask. Looking at it one way, Dermatologists are taught to think skin types I-VI which refers only to the amount of melanin (our microscopic pigment granules) in our skin and the amount of sun protection that melanin gives us. Skin type I is a red head with almost no melanin sun protection and skin type VI being ebony with a lot of sun protection and every color in between. Hope that makes sense.
Skin types as in oily, dry, combination, acne-prone etc are lay terms that are used by the consumer cosmetic and skin care companies but have been adopted by the Dermatology community too to make communication with our patients easier. The usual 5 (oily, dry, normal, combination and sensitive) seems a little simplistic to me but, conversely, some systems out there have 10-20 types which seems unnecessarily complicated to me. We need to come up with something in between. Write back if I got your question completely wrong! Dr. I