It may be due to severe UV rays on to that particular site. Other cause may be due to severe
repeated flexion of the arm. This can be treated by Ointments or creams.
It may be due to some viral or fungal infection. Sometimes it may be an allergy to a medicine. If there is any swelling on the lateral part of elbow,it may be Tennis elbow. It is better to show a skin specialist very soon.
You did not say how long these bumps have been there, but if not for long and if it is the only place on your body where you have them, then it could have been caused by a spider bite.