Why do my bras leave red marks?

Bras leave red marks because of uneven pressure and friction against your skin from inadequate design or poor fit. When a bra doesn't provide proper support, it creates concentrated pressure points that press into your skin rather than distributing compression evenly.

Materials play a significant role too – low quality fabrics trap heat and moisture against your skin, which can lead to irritation. 

The engineering behind truly supportive bras involves careful design that works with your body's natural movements and contours, preventing that uncomfortable digging sensation that leaves those telltale red marks.