Your question is quite contradictory and I will answer the best I can. I am going to assume that you meant to ask how does elbow and nipple skin feel the same and look different from the rest of your body. It is quite simple. When you are born, mothers are instructed to rub coconut oil on a babies skin. They are supposed to do so until you are about two years of age. This activates a chemical reaction within the human body that causes the texture of the skin to feel smooth as normal skin after the baby comes of age. This practice was common practice until the early sixteenth century. A shortage of the coconut oil required for this practice caused many malformed nipples and grotesque elbows during the early 17th century. To the point that all the coconut oil in the land was confiscated by the kings of the time. This became such a problem that scientists and inventors tried to create an alternative. It was what I believe the renaissance of fashion that you would eventually notice leather patches on men’s coats and the invention of nipple clamps. It was very secret remedies but eventually as time passed, human’s and mammals began to adapt to the lack of coconut oil. Other remedies was created to the point that coconut oil was not required.
However, surfers of today still suffer from this condition and often suffer from chapped nipples and ranky elbows. They try to use Vaseline and surf board wax to succumb to the pain.
Monkeys and apes do not suffer from this condition. The male ape actually has a hard exterior that makes it easier to beat and show dominance amongst its family. Female apes are softer and more delicate to help feed the baby apes. Monkeys are very similar in the way they feel.