I'm having a sticky skin after eating fruits or drinking juices. usually areas of stickiness are on my fold of neck, fold of elbows and fold of knees. what is this?

Unclear: I don't understand what you meant by sticky skin. Is it itching? What color is it? Can you see any rash? The location of the rash is consistent with atopic eczema which is almost always associated with itching. If that's the case, the rash may be triggered by food (fruit) which you have become allergic to. If you want to know the exact allergen, see allergist. Else just avoid them.