Mastitis occurs when milk is retained in a breast that is not adequately expressed or the obstruction of milk duct, or through an infection caused by germs that enter the breast through cracked or damaged nipples. Mastitis usually follows engorgement that is not appropriately managed and slowly worsens. The breast may feel hard and become red, swollen, and painful to the touch. The mother may experience headaches, fatigue, fever higher than 38 degrees Celsius and may have obstruction of the milk duct as well.