Mastitis can occur whenever a breast stays full for too long. If you get it, it's usually a sign you're trying to wean too quickly. You will probably find that by slowing down the pace, you can avoid mastitis. Start by dropping one daily breastfeeding session, and give your body three to four days to adjust your milk production downward before dropping another. If at any time your breasts start to feel full, express just enough milk to make yourself comfortable — but no more. Repeat until all breastfeedings are replaced with breast milk substitutes and you no longer feel the need to express.