I don't know if it hurts the chicks,but I try not candle(not all the time successfully,lol) very often. I don't think it's good to handle the eggs any more than you have to. I just had a broody hen hatch 9 chicks out of 9 eggs. I had her in a cage,by herself ,in a wooden box for a nest. I never candled and really didn't bother her at all except to make sure she had food and water. Apparently hands off worked.