What's the role of BSA/Milk as blocking agents??

Both BSA (bovine serum albumin) and milk are two of the most commonly used blocking buffers and are important in preventing nonspecific binding of antibodies to tissue. Milk is cheaper and easier to prepare compared to BSA, but it should not be used to detect antibodies that target phosphoproteins since it contains casein which is a phosphoprotein. Milk should also not be used with biotin detection systems as it contains biotin. On the other hand, BSA should be avoided when using lectin probes since it contains carbohydrates which can increase background.