What is the difference between a blocked duct and mastitis?

A blocked duct causes a firm, tender lump in one area of the breast, usually without fever. Mastitis includes the same lump plus redness, warmth, and systemic symptoms such as fever above 101°F (38.4°C), chills, and body aches, caused by inflammation or infection of breast tissue.

For a blocked duct, continue breastfeeding or pumping frequently on the affected side, use gentle lymphatic drainage massage toward the chest wall rather than deep tissue massage, and apply a cold compress between feeds. Most blocked ducts resolve within 24-48 hours with continued milk removal.

For mastitis, fever, chills, or symptoms not improving within 24 hours of frequent milk removal require medical evaluation, since mastitis can progress to a breast abscess if untreated. Continuing to breastfeed or pump through mastitis is safe and recommended and does not harm the baby.