I will tell you have funny story of when i tried to express my milk. Lo was sleeping and my boobs were going to exploded if i did not express, so i got my pump, and followed the instructions, but it was too much me, i nearly made my nipple explode, It increased by size but about 3 or 4 times bigger than it should have been. i was so scared i ran downstairs down the the MIL who was here at the time and shouted "here take a look at my nipple". She nearly wet herself laughing at the size of it. MIL replied "blimey look at the size of that" LOL. after putting ice on it, it returned to normal in an hour.