There could be a few reasons but a common cause of sudden nipple pain is thrush, or a yeast infection. This pain often feels intense or “burning” with shooting pains deep into the breast. It occurs both while nursing and between feedings. It is not improved with correcting baby’s latch. (For more information see FAQs Thrush.) Other causes for sudden nipple pain can be:

• teething or other changes in your baby’s mouth that affect how he latches on
• changing nursing patterns (if your baby spaces out his feedings, flow may be faster and he may adjust his latch to cope)
• pregnancy
• use of an ineffective breast pump
• skin reactions such as eczema and psoriasis
• skin infections such as herpes and chicken pox (You would also see sores on your breast.)