Skin itchy and numb?
It probably is just from histamine release from an allergy or sensitivity, don’t scratch it anymore. It could be contact dermatitis (A reaction from something that came in contact with your skin)
These 2 above will go away
Is their bumps, what does it look like?
Also some people have on their upper arms
keratosis pilaris (if you have had this for a while)
you know what im tlaking about, bumps on your upper arms and shoulders
its from a buildup of dead skin cells
go to the doctor for this, they can prescribe