WASHINGTON (AP) — You’ve likely heard it since childhood: Don’t scratch that bug bite or rash, you’ll make it worse. But why would something that feels so good be bad? A lot of things can cause itchiness, sometimes serious diseases . Whatever the cause, doctors have long warned that scratching too much can damage the skin . Now researchers better understand why even a mildly annoying itch could put you on an itch-and-scratch cycle if you give in. How did they find out? In part by putting tiny “