Why does my bra leaving dark marks under my breast?

If your bra is leaving dark marks under your breast, it may be because the bra you're wearing is too tight. Wearing a bra that's too tight can lead to skin pinching, red marks, bruising, and pressure. 

If your bra is too tight, you can adjust the straps to make them longer and adjust the band to a looser row of hooks. If your bra is not adjustable, or if those adjustments do not fix the problem, you'll need to try a larger bra size.  

If your band is too tight but your bra cups fit well, go up one band size and down one cup size. If both your band and your cups are too tight, go up one band size but keep the same cup size.