What is a blocked milk duct?

Theory and thinking about "blocked" milk ducts has recently changed.  We now know that when breast milk moves through the milk ducts, flow can be impeded by inflammation and swelling within the ducts themselves. This swelling narrows the ducts, and can cause a back-up of milk behind the "blockage" which creates the feeling of a lump or bump in the area.  We now know that a "block" or "clog" is not thickened lump of stagnant milk in the duct as the name previously suggested, but rather,  a pool of milk behind the narrowed inflamed area.  Treatment involves reducing the swelling within the duct itself to allow the milk to flow again.  Blocked milk ducts may be painful,  red and swollen on the surface area of the breast above the block. 

Sometimes you may notice a whitish, blister-like bump on the nipple known as a "bleb" which often has an associated area of "blockage" in the breast.  Blebs often resolve spontaneously  or may require warm compresses, topical steroid cream or possibly manual opening to resolve them.  

Most blocked ducts will resolve on their own with conservative treatment within 24-48 hours, but some blocks may be persistent and come and go.  Therapeutic ultrasound can be helpful to help decrease the inflammation in the "block", helping the duct "open".  Occasionally a block may progress to bacterial mastitis which is an infection in the breast requiring antibiotics.  You may have an infection if you develop a fever, chills or malaise/body aches/feeling unwell.

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Blocked milk ducts can have many causes, such as a high milk flow or an inefficient latch or suck, which then may result in nipple pain, and/or incomplete emptying of a part of the breast.