31 July 2026
Why the underwire pokes you
The wire is the wrong width for your root, so it lands on breast tissue instead of the bone behind it. A wire narrower than your root sits on tissue at the outer edge and digs. A wire wider than your root oversteps onto the ribs at the side and stabs under the arm.
What is happening
Your root is the footprint where your breast joins your chest. A wire is meant to trace the outside of that footprint and rest on the ribcage all the way round.
Too narrow, and the wire crosses your tissue at the side. It has soft ground under it, so it sinks in and leaves a sore line, usually under the arm or at the centre.
Too wide, and the wire runs past the root onto the ribs. Now it has no tissue to follow and every arm movement drives the end into you.
How to check it on yourself
Press two fingers flat where your breast meets your ribs at the outer edge and follow that line up towards your armpit.
That line is your root. Take the bra off and lay the wire beside it: the wire should end where the root ends, not before and not past it.
What to change
Cup size changes wire width. A bigger cup on the same band comes with a wider, deeper wire, so a narrow wire on tissue is often a cup problem.
For a narrow root, look for plunges and vertically seamed cups, which are cut on a narrower wire. For a wide root, balconettes carry a wider wire without stabbing.
Then fix the band. A loose band lets the wires travel off the ribcage entirely, and any wire pokes once it is off the bone.
What will not fix it
Wire cushions, moleskin and bending the wire by hand. All three treat the pain and leave the geometry alone.
A wireless bra also does not fix it. It removes the symptom, and you lose the support you bought the bra for.