• Milk stasis
• Microbial Infection

Milk Stasis (Stagnation of Milk):

• Milk stasis is the primary cause for development of lactation mastitis, which may or may not be accompanied with infection. 
• Milk stasis results from stagnation of milk within the breast due to inefficient removal of milk. 
• Infection may also occur in Milk stasis as the stagnant milk may provide a good nutrient supply for the growth of bacteria.
• Lactation mastitis may occur when the breasts are filled with milk soon after delivery and milk is not removed by the infant from the breast, which may be due to:
• Poor attachment of the infant to the breast
• Ineffective suckling
• Restriction of frequency or duration of feeds
• Blockage in milk ducts
• Increased milk supply

Microbial Infection:

Common microorganisms found in mastitis 

• Staphylococcus aureus
• Staphylococcus albus
• Streptococcus species
• Escherichia coli