Anesthesia for injection

Hi,
I recently came to know that there was anesthesia through sprays. We could spray anesthesia on the skin and that area would become numb.
Now, why isn't this used in clinics and hospitals for injections. I mean , doctors could spray anesthesia on the skin and then administer the injection , right?

Why is this not being done?

[farziin]

i agree u .but the design of needles &operator r importeant . alchol pads r useful &provide enough anesthesia in surface . also u may ask for spray &they should do this .do u have exprienced needels penetraating youe skin by accident . the main thing which makes us panic is bleeding &the idea of injury . so be sure the majority of the medical staffs r trained 4 painless injections . next time just warn them & ask 4 spray