Hello. Thank you for writing to us at healthcaremagic I suggest possibility of keratosis pilaris, which present as small, pin head sized bumps on the outer aspect of arms. It is not an infection and therefore I doubt that you got it from your sister. They are more common in those who have dry skin and on sliding hands over the affected skin, they are felt as rough skin. The bumps form due to accumulated keratin around hair follicular openings. On close examination, hair can be seen trapped in the accumulated keratin. Treatment is with with regular use of a topical keratolytic cream/ moisturizer e.g urea, lactic acid, glycolic acid, salicylic acid which helps exfoliate accumulated keratin. An Oral Vitamin A supplement is also helpful in this condition. I suggest that you visit a dermatologist for a confirmatory diagnosis as well as appropriate prescription. Regards