Weird, after doing several shots of H a day for like 8 years, often re-using cottons, I never once had cotton fever. I was aware of it, and during the time I was using H daily, was under the impression that it was caused by a cotton fiber, so after pulling up, I would always hold my point to the light and look for any fibers on the needle. Occasionally I would see one and get it off before injecting. Never did catch cotton fever, thankfully, I had seen friends with it and it did NOT look like fun .