Hello, My Stepson Is 12 And Has Developed Rough Bumps

Hello, my stepson is 12 and has developed rough bumps on both of his elbows. They seem to stem from the elbow and kind of sporadically "creep" up/down his arms, however they are thickest on the elbow. The bumps are not puss filled and are hard, and white in appearance. He has had them for 3 weeks now, and while they started to clear up while using a hydrocortisone cream for 10 days, they seem to be coming back slowly now that he has stopped. He does have allergies to certain grass and had been playing in it quite heavily when these first started to appear. If it is an allergic reaction, is it normal for it to last this long and not fully go away? Is there something else it might be?

Thank you,

Chelse