Thanks for the query to ATD for an opinion.
The presence of small bumps all over the arm indicates a rash over the exposed or uncovered areas of the skin. So it is likely to be an allergic rash or a contact dermatitis following contact with an allergen. As the rash is restricted to arms and not over other exposed areas like neck or face, it is unlikely to be induced due to sun exposure.
It is suggested that you may opt for an antihistaminic like Tab CETRIZINE 5mg twice a day for alleviate any itching ( minimal dose) and also after washing your arms with warm water without soap , shall apply an emollient or lacto- calamine lotion for soothing effect and decreasing the rash.
If the rash doesn't subside even after the procedure in next 24-48 hrs, then you may visit your physician for a local examination and an allergy screen.
I hope I have answered your query in detail,
Wishing you good health,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.