Hi It seems your grand daughter has pimples developing in arms and back. Most pimples are caused by an accumulation of oil and bacteria which clog the pores. For this, a cream or wash containing salicylic acid or benzoyl peroxide may be beneficial. Washing thoroughly, especially after sweating, is also recommended. Pimples are often caused by bacteria and naturally occurring bodily oils which can clog and cause a minor infection within the pores. The first step in avoiding this is to wash regularly, once or more per day, to cut down on oil. Some individuals may have an overproduction of oils, so products which contain salicylic acid are often beneficial because they help dry the skin and draw pus from infected pores. Sweat can also contribute to pimples and should be kept at bay. Those who sweat profusely may have to wash more often than others and wear an antiperspirant. It is important to note, however, that antiperspirants can also clog pores, making the problem worse. Choosing an hypoallergenic variety may help. Avoiding products with fragrances and other skin irritants may also reduce skin reactions. For further questions, do contact us.